Hi, brand new to the forums here...So I am starting an RD250 restomod project on a '73 RD250 blending it with some superbike style and vibe. My challenges right now are trying to spec the engine upgrades that give me the best balance of reliability, cost and power, kind of in that order. My 2 stroke experience is many years with a CR250 but never cracking the cases or anything like that so i'm starting pretty blind here. I've got a good set of expansion chambers already, custom for the '73 but beyond that, do I go for a overbore kit with pistons/rods/bearings (if so, how big, 300, 350?) If i go that route, do i need to completely upgrade the transmission and camshaft as well? Can I get decent power increases without an overbore kit (with the chambers alone) and by doing some mild porting, upgrading reeds, maybe the head etc? For philosophical reasons I want to keep the costs down as much as is possible/reasonable. I want to produce something original and unique without breaking the bank. I know i'll spend more money than I intend, and i'm well aware of the mantra "speed don't come cheap" but I can start with good intentions at least. Any thoughts or tips would be awesome. Attached a pic of the bike right before I stripped it. I've had it for over 35 years and struggled with doing a stock restore or something hooligan-ish...hooligan won out easily in the end. :-)
an aftermarket 350 topend is the easiest/cheapest way but you also need to find 350 heads & 350 wristpin bearings.
chambers, jetting and a really solid ignition will keep you very happy w it. TBH, fitting aftermarket replacement 350 baffles to the stock 250 pipes and the 350 jugs will make a difference as well.
there really isnt any benefit to over boring stock cyls to get power on these. just, isn't. you'll break thru the liner before it makes any difference
also, if you don't know when the crank seals were last done, plan it it.
https://www.2strokeworld.net/forum/index.php?topic=5650.0
and welcome to the forum.
Welcome! :cheers: your bike appears to be a 1974 RD250A based on the Amber Brown paint. It should have a frame and engine number starting with 352-2xxxxx. A '73 would be Butterfly Blue.
Looks like it's all stock. Just needs a new taillight lens. Do you have the carbs? I would recommend not going overboard on the mods, and keeping all the take-off stock parts. That way it can always be put back to stock if you or the next owner wants to. An original stock bike will tend to will have a higher resale value than a modded one that's been personalized.
If you want to increase the displacement you can't really do that with an overbore since you're only gaining a few millimeters of bore at a relatively big cost. Better to just install a RD350 top end on it. The 350 top end from '73-75 will both right on. There are a few threads on this site covering it. If you want to keep costs down, some members here have had good luck with the Chinese cylinders/piston kits available on eBay. A few threads on that topic here too.
EDIT: looks like Mark was faster on the keyboard and posted while I was still typing. :wink:
What they ^^^^ said. Personally, FWIW, i would not worry about reliability. I had a very modded 350 and had no issues. If you take your time and build it right and listen to the experience on the forum you will be fine.
wow, thanks for all the quick replies. seems then like a 350 top end is the way to go, had no idea you could just bolt one on, i'll search the forums for info as suggested. to answer a couple of questions above, the head tube tag/sticker says '73 on it but I guess that must just the production date, not the model year since the numbers match what was mentioned above for a '74. I do have the carbs and the tail light lens but the slides seized from sitting for decades so i took them off to free them up. This bike will be with me til i'm dead so no need to worry about resale value or anything, the goal here is to build a fun little ripper with some fresh style that makes babies cry as it flies by. thanks again for the advice, keep it coming, i'm sure i'll have tons of questions! really appreciate all the historical/institutional knowledge here.
re: bolting on 350 top end on 250- Isn't there a difference in cylinder studs and/or bolts that needs to be addressed? Could be a Senior memory fart :umm:
Quote from: RDnuTZ on April 04, 2025, 10:32:13 AMre: bolting on 350 top end on 250- Isn't there a difference in cylinder studs and/or bolts that needs to be addressed? Could be a Senior memory fart :umm:
There is a difference in length, the 250 studs are shorter. I have done it without changing the studs and have not had any problems.
same.
if you want to get the 'correct' ones yambits sells them new, but it def isn't necessary
Economy Cycle (https://www.economycycle.com/shop/yamaha-rd250350400r5ds6ds7-parts/engine-related/engine-mounts/rd250-350-r5-rd400-cylinder-studs/) sells the studs: Yamaha 90116-08064-00
It's not that costly to replace them all
didn't know john had them. sweet. :cheerleader:
when swapping 350 top end onto 250 lower end, does oil pump need to be swapped as well to maintain proper mixture ratio?
absolutely not. been there done it. as long as the primary gearing and clutch stay '250' it's fine.
Quote from: m in sc on April 05, 2025, 12:49:23 PMabsolutely not. been there done it. as long as the primary gearing and clutch stay '250' it's fine.
Just go one tooth larger on the front sprocket or you'll be WAY wheelie-prone!
Quote from: Jspooner on April 04, 2025, 11:14:30 AMQuote from: RDnuTZ on April 04, 2025, 10:32:13 AMre: bolting on 350 top end on 250- Isn't there a difference in cylinder studs and/or bolts that needs to be addressed? Could be a Senior memory fart :umm:
There is a difference in length, the 250 studs are shorter. I have done it without changing the studs and have not had any problems.
Quote from: m in sc on April 04, 2025, 11:52:10 AMsame.
if you want to get the 'correct' ones yambits sells them new, but it def isn't necessary
If I may jump into this thread and hopefully anybody else may find my experience useful. So as some of you may recall I am into this 250/350 conversion myself and to late to turn back. I have the parts required. The cheap Chinese 350 top end from Ebay along with a pair of mismatched 350 cylinder heads that I did my best to clean up.Also have the 350 wrist pin bearings exhaust manifold studs,and a gasket kit. I even have the correct 350 cylinder studs...and the old 250 top end is already off the bike.
This is where the road to hell is paved with good intentions. :undecided: With three of the 250 cylinder studs off the engine I only have five more to go. I can say for sure having measured the shorter 250 studs there's a difference of a quarter inch in length compared to the 350 studs. I hope you fellas are correct that it isn't necessary to use the 350 studs because I am having a hell of time trying to free up at least two of the studs on this engine. I've been using the double nut method with a third nut being the special nuts that bolts down the cylinders and heads, I like that better than clamping down on the stud with vise grips. :undecided: Also had to heat em up with a Map gas torch and I tried PB Blaster and I just can't get a couple of these studs free doing all that. :confusing2: The one closest to the oil pump I managed to partially sing/burn the oil tank sending line, the three holed grommet it goes thru and a bit of the fancy rubber protective Vape boot routing the alternator lines. :dislike: Yeah I did make a heat shield with some metal scrap to protect most of that stuff after the fact but too late to cry over that. :sad:
I'm gonna try to get as many of these studs out as I can but I think I may have to settle on not getting them all. :sad: Just seems like it would be nice though as the 250 studs only seem to allow a wee bit more of three full turns with the special nuts, unless I omit using the washers?...that's probably not a good idea but it would give some of the nuts on whatever remaining old 250 studs more purchase.
Well in theory I think more threads(350 studs) to bolt down everything is better but it seems like a rabbit hole to try to get out the old 250 studs. I don't want to ruin the threads. if they will work just fine may not have a choice unless you want a bigger project extacting studs or even ruining the upper case half? :shocked:
you need a stud removal tool like the 1 Mark recommended some time ago. I used to struggle with removing using Primitive Pete methods as well until I saw Mark's, so I went to NAPA and got 1 of these and they come out easy (using Blaster does help too)
https://www.jegs.com/i/JEGS/555/W83203/10002/-1?msclkid=1e0b40afb9fa13619be7275c8384e7d7&utm_source=bing&utm_medium=cpc&utm_campaign=WP_US_Bing_Shopping_555_Hybrid_Category_Catchall&utm_term=4581664973605614&utm_content=555%20Products
I used it multiple times on various sizes and it's great.
Quote from: RDnuTZ on April 06, 2025, 10:43:07 PMyou need a stud removal tool like the 1 Mark recommended some time ago. I used to struggle with removing using Primitive Pete methods as well until I saw Mark's, so I went to NAPA and got 1 of these and they come out easy (using Blaster does help too)
https://www.jegs.com/i/JEGS/555/W83203/10002/-1?msclkid=1e0b40afb9fa13619be7275c8384e7d7&utm_source=bing&utm_medium=cpc&utm_campaign=WP_US_Bing_Shopping_555_Hybrid_Category_Catchall&utm_term=4581664973605614&utm_content=555%20Products
I used it multiple times on various sizes and it's great.
Have you used this to remove a cylinder stud? With the bottom end still in the bike? I would think the engine being in the bike would help to hold it in place but I am nervous that I could do greater harm ruining the stud trying to remove it. I looked at the tool reviews and one them said that it's possible to shear off the stud there by necessitating to drill it out and retap it.
Do I really need to remove the studs at all? I do think it makes sense to use the longer 350 studs but I just have a bad feeling that at least a couple of these studs are really stupidly stuck and although a tool like this may work OTOH if it doesn't and the engine is already out of the bike that's one thing by all means drill and tap em out. However maybe I am just making a mountain out of a mole hill?
PS- I did split these cases sometime ago not really knowing any better and thought it a good idea to replace the seals and gaskets, I also put a Vito's crank in it. That was about 4 thousand miles or so ago. I never bothered to remove the studs as they seemed fine as is except one of them was like finger tight and had some balled up threads so I replaced it. I can say they are not loctite in. Just been there a long time. I do have a funny issue trying to read the oil level ( oil level reads like an inch or so over the upper level when cold) like it doesn't return very well,I suspect from the crankcase to the clutch cover side and I assume there may be some excessive Yamabond obstruction causing this but I don't really know. I think maybe I used too much of it, quite possible I did, I know I put on surfaces like the cylinder base gasket that don't require it. Well once the engine warms up and I run it for like a minute, the oil level reads proper upon a recheck and I just always measure out what I put in the bike which is what's specified. Just pondering a worst case scenario should I have to perform surgery but I do think that's a last resort. As much as I would like to right the wrongs of my past repair work.
Either that Jets tool, or the clamping puck style.
https://a.co/d/cuEJHyn
I have this similar tool and I got all of the nasty gt750 studs out with it.
My RD I caveman double nut and heated them. Then gave up and got the tool.
If you decide against it you have to run the nuts without washers on the short 250 studs.
But since you started, hit the actual stud with your torch and get it pretty hot, then soak it with penetrants. Then crank until it comes off. It'll let go eventually with the old heat juice method.
ive pulled the studs w the motor in the bike before.
Quote from: Striker1423 on April 07, 2025, 12:19:45 AMEither that Jets tool, or the clamping puck style.
https://a.co/d/cuEJHyn
I have this similar tool and I got all of the nasty gt750 studs out with it.
My RD I caveman double nut and heated them. Then gave up and got the tool.
If you decide against it you have to run the nuts without washers on the short 250 studs.
But since you started, hit the actual stud with your torch and get it pretty hot, then soak it with penetrants. Then crank until it comes off. It'll let go eventually with the old heat juice method.
Yeah when I was hitting the studs with heat the longest I had the torch on one was about 20 to 30 seconds. I gave up as soon as I started burning the oil line/ square three holed grommet. Interestly I got one more stud out last night before going to bed, all the exhaust side studs are out but all the intake side studs are just too cozy there. I guess I can try what you suggest, I did order replacement rubber bits. If I run it the remaining 250 studs minus washers, those washers only give about 1/16" extra threads.
When I was putting heat on the studs I directed the flame to the stud meets case. I thought it better to get the case warm there but maybe it just takes longer to warm that extra surface area?
I dunno the tools are cheap enough in price but what is the better stud remover?...the one you recommend that looks like a socket or the one that RDnutz recommends?
Quote from: m in sc on April 07, 2025, 07:20:47 AMive pulled the studs w the motor in the bike before.
Yeah well it does make sense in more ways than one. I just felt like if I was in a different situation with the cases split then I would be more brave. I am so nervous about wrecking the studs or just case if that makes sense. It does seem like that stud removal tool maybe the way to go though.
Well I gave it another go with the heat on the stud. Did a better job covering flammable parts nearby and really put the heat to one stud till it was glowing red for a second or more. Took the heat off and immediately went at with the double nut method and it still wouldn't budge. Gave a few squirts of blaster and tried a second time, mind you I soaked it with blaster last night before bed and same thing, won't budge a bit. The only movement I get is the nuts wanting mash each other and the only give feels like in their threads so I back off.
I dunno what to say except the same scenario goes thru my mind,If I plan on more engine work like say a crank replacement or even just replacing crank seals then OK I'll go to town with the stud remover tool. However those removal tools just look like they may very well work but with a good chance at ruining perfectly decent threads on the studs that in theory may well be OK to use as is.
So let me as this I think I am going to chance it with the shorter 250 studs that are stuck in there. I'll just not use the washer for that extra bit of threads that would give me. Is it ok to not use the washers? I guess I just have to me mindful of frequently checking torque values? The heads seem like they got more than enough material to em. I don't think the nuts would seize up on them, which I could just put a bit of anti seize on them?
I wish there were longer nuts with more threads knowing that folks would do these 250/350 conversions.It is interesting to figure out just how much thread depth you really need to keep it all together given all the vibration.force of the engine running. I know I had to retorque the nuts occasionally as a stock 250 but I also never checked them often enough.
I had several damaged Yamaha MX & YZ case halfs laying around to practice on with that stud extractor tool. Patience is a virtue here. I've typically soaked a stuck bolt or stud in PB Blaster or similar and walked away instead of hitting it right away. When I come back to it, I lube it a little more and begin trying to loosen - but I also go a little in tightening direction too just gently working back and forth to see if it moves at all either direction. Once I can tell it is actually loosening (instead of weakening and ready to snap) I give it some more Blaster and walk away and keep repeating this process over time. Haste makes waste :twocents:
I'm also wondering if shortening the head hold down bolts a little instead of ditching the washer could work? I haven't gone out to the shop and measured anything but just brainstorming (or farting) a little from a distance.
look you can run them as is, ypu don't need to swap them. however it makes it easier to clean the top of the case. worst case is you helicoil the case. these studs see 15-20 ft lbs of torque so not a big deal. I've never had the stud tool fail me, ever. I literally just stripped 3 sets of rz cyls and had to pull all the studs out a few mos ago,used that tool and none were damaged. bit of oil, hit it with my Dewalt nut runner and they all zipped right out
Quote from: RDnuTZ on April 07, 2025, 10:08:00 AMI'm also wondering if shortening the head hold down bolts a little instead of ditching the washer could work? I haven't gone out to the shop and measured anything but just brainstorming (or farting) a little from a distance.
Yeah I tried putting the 350 cylinder and head on and tightened it up just finger tight and I think I counted a bit over three full thread turns now without the washer I'm guessing over four turns. Mind you that's not even fully tightened to torque value spec. I did measure out about an inch of thickness where the studs pass thru on the head.My heads being what they are a mismatched compromise of functionality,value and aesthetics...if I had the means I would be tempted to take quarter inch cut off the top of the stud holes just to get the nuts to suck in deeper and I don't think it would hurt em. It would just make them more unique for my top end build. Of course not the right way to do it and sooner or later one may need to just replace a stud anyways. Those studs that are stuck are the original 50 year old parts,doesn't surprise me they like being at home there. FWIW
Quote from: m in sc on April 07, 2025, 10:21:50 AMlook you can run them as is, ypu don't need to swap them. however it makes it easier to clean the top of the case. worst case is you helicoil the case. these studs see 15-20 ft lbs of torque so not a big deal. I've never had the stud tool fail me, ever. I literally just stripped 3 sets of rz cyls and had to pull all the studs out a few mos ago,used that tool and none were damaged. bit of oil, hit it with my Dewalt nut runner and they all zipped right out
OK good to know I think I will just run it with em. It'll be easier for me, I'm kinda lacking in tools as I don't even have an impact wrench never mind the stud remover tool. Just as an aside when I pulled the cylinders off there was road sand etc, inbetween them. :shocked: I should've known( but really have very little experience with engine building), I was careful not to get that stuff in the crank, cases but I think there are so many variables that can just go wrong with this build anyways that for one reason or another I may very well do more than I bargained for. Gotta at least try to keep it on a budget :smiley: I still feel bad about boogering a few rubber bits with the heat but live and learn.
I did watch one video of a fella on you tube.He used propane gas and laid flame on the stud for what seemed like a minute and half with a few pauses and used candle wax and the double nut method. It was an exhaust stud and the head was outta the machine. Not sure if there is an advantage to candle wax vs. penetrating oil but it looked good.
You might also freeze the studs with aerosol freeze spray before trying to remove...
Bringing this back around a bit to the cylinders themselves, is the only place to source them from Ebay or Amazon? Are there any US distributors? I'm generally not one to take a chance on Ebay/amazon stuff these days unless as a last resort. I do see US manufacturers of the piston and rod kits needed for the 350 top end (Wiseco etc). And then just asking again, does the crank require a rebuild/refresh at that point to handle the extra power? This bike has 12k generally well maintained (as far as I can tell) miles on it. I don't have a clue as to how much the lower end would need done to it to be fresh and ready to run a 350 top end. I just assume at this point refresh the bottom too? But if people tell me it is ok to use the bottom end as is and just need some fresh pistons and correctly sized wrist clips, I wouldn't be unhappy going that less labor intensive route. But it does seem like doing it right requires refreshing the lower end. Ideally I would love an ordered to-do list of all the basic things your should do when doing an RD engine restore so I get it right the first time as well as can spec out the budget more accurately. I do seem to be able to pull that list together though from a number of posts here.
For stubborn studs, if there's access, I like gronking down on the stud in my vice and using the case to get more leverage and torque the stud out.
if you don't know the age of the crank seals, change them and the bearings are worth a look. mileage really means.. nothing. I had a 5k mile motor with cranked and dead crank seals a few yrs ago, condition of crank itself is ? unless you inspect it. My 70 r5 just got a new crank at 27K. it was still running fine but was def time. so, its a case by case situation.
Me? at this age on a (previously) stock bike is minimally do the crank seals if the crank is quiet.
also, you need wrist pin bearings (wider) from 250 to 350. and no, just get the ebay cyls, they are fine, the link is in the post i put up before. No one else is carrying them as far as i know.
Quote from: m in sc on April 07, 2025, 05:55:47 PMif you don't know the age of the crank seals, change them and the bearings are worth a look. mileage really means.. nothing. I had a 5k mile motor with cranked and dead crank seals a few yrs ago, condition of crank itself is ? unless you inspect it. My 70 r5 just got a new crank at 27K. it was still running fine but was def time. so, its a case by case situation.
Me? at this age on a (previously) stock bike is minimally do the crank seals if the crank is quiet.
also, you need wrist pin bearings (wider) from 250 to 350. and no, just get the ebay cyls, they are fine, the link is in the post i put up before. No one else is carrying them as far as i know.
all excellent info, thank you! it sounds like you can simply put the 350 pistons on the 250 rods with a wider wrist pin and bearing, that seems almost too easy.
the key i've found so far is be sure to make progress every day, even if it is just a little bit. no different than any big project but daily progress adds up quick on a motorcycle as long as you avoid going too deep down the rabbit hole. easier said than done sometimes, it is motorcycles after all.
so i read your thread m in sc on those cylinders, seems like they require quite a bit of prep to be ready or maybe optimal...is there a shop or machinist here that you recommend to prep them the way you did? followup, looks like HVC Cycle in Nebraska is sort of one stop shop for all engine things RD.
and what do you know, ebay has them right now with a coupon you can apply for $30 off so they come in at $161 +tax. https://www.ebay.com/itm/284771396485
.
Crayons work better on steel studs in aluminum than penetrating oil if you are using heat. The wax doesn't evaporate as easily. The oil just burns off. Use several heat cycles on them to let the wax get down as far as possible into the threads. Some people say metallic crayons work better. At least silver is a better match on aluminum.
IR8D8R
Quote from: IR8D8R on April 08, 2025, 03:13:38 PMCrayons work better on steel studs in aluminum than penetrating oil if you are using heat. The wax doesn't evaporate as easily. The oil just burns off. Use several heat cycles on them to let the wax get down as far as possible into the threads. Some people say metallic crayons work better. At least silver is a better match on aluminum.
IR8D8R
Interesting to know. Now is a crayon different than candle wax?...I did watch a video of a stud removal with the wax being used.Seemed to work nicely but as it was demonstrated the heat was put on much longer than I felt comfortable doing myself. I would say a solid 45 seconds then the candle was nudged into it and this was repeated three times on a steel exhaust stud in aluminum.
I got nervous with wiring and gas being so close to the work area, not to mention a bit impatient putting the heat on those studs so I gave up on it. Saying all that even after learning from my mistakes of not covering wires and rubber bits so close to the work area...and like you say it seemed like I was just burning off the PB Blaster I was using.
That and the fact that m in SC emphasized that I could get away with the shorter studs. For better or worse I proceeded with the install and at present everything except the carbs are reassembled. Not sure if it was a bad idea or not but I dabbed a very little bit of anti seize on four of the studs I did manage to remove prior to assembly.
[/quote]
all excellent info, thank you! it sounds like you can simply put the 350 pistons on the 250 rods with a wider wrist pin and bearing, that seems almost too easy.
the key i've found so far is be sure to make progress every day, even if it is just a little bit. no different than any big project but daily progress adds up quick on a motorcycle as long as you avoid going too deep down the rabbit hole. easier said than done sometimes, it is motorcycles after all.
so i read your thread m in sc on those cylinders, seems like they require quite a bit of prep to be ready or maybe optimal...is there a shop or machinist here that you recommend to prep them the way you did? followup, looks like HVC Cycle in Nebraska is sort of one stop shop for all engine things RD.
and what do you know, ebay has them right now with a coupon you can apply for $30 off so they come in at $161 +tax. https://www.ebay.com/itm/284771396485
.
[/quote]
That's the same seller I bought mine from and I thought I got a good deal $181.86 with tax. They arrived super quick from Texas to where I am in Ma. in like four days from ordering. I was impressed, really well packed in a thick styrofoam box inside a carboard box.
I'm definitely not an engine builder/expert as far as what to look for in quality of cylinders and pistons but from what I could see everything was ready for assembly. Like you I read the topic/thread m in SC started about these cheap cylinders, up to that point I was hesitant to get em. I read all the horror stories. The only thing I did to prep mine was cleaning the protective oil film on the bores also I noticed some small metal chips, just a few left behind from machining processes. I did radius that center middle tab on the intake side of the piston skirt just because m in sc did it,seemed like a good idea...but I don't know if you need to. I left the ports as is regarding smoothing out rough surface castings because admittedly I am not an engine tuner.
Yeah I just bolted it all together this morning. Had the hang up with four of eight cylinder studs not wanting to come out easily so I left em as is being impatient as I am and trusting that there's enough threads to bolt it all down. Now I can attest I omitted using the washers on the cylinder head just to get a little extra tightening the nuts and they fastened down just fine. You do get an extra quarter inch of threads with the longer 350 studs. It's what's recommended and designed by Yamaha but you will have to spring for those longer studs $5 to $9 bucks a pop(shop around), there's 8 of em plus the $20 to
$30 stud removal tool.Still gotta put on the carbs so I haven't fired it up yet but I did cycle the kick start a few times and she turns over quite nicely in the sense that nothing sounds weird of binding up if that makes sense. I do think there is a certain cheap quality to the pistons but I dunno. It just seemed like the rings were tedious to keep well seated in the grooves and centering ring gaps in relation to the locating dowel pins of the piston,as I was holding each cylinder seating them to the pistons during assembly. I dunno maybe I just needed a third hand or there is some kinda engine builders secret? So in stating that I can see maybe why some folks splurged on different pistons.
Don't forget you also need the bigger 350 heads. Gotta find em used or maybe get some pricey aftermarket upgraded ones.
If these cylinder kits get any cheaper.[/url
Not sure how legit this Ebay seller is but they also offer more savings if you buy in bulk. (https://www.ebay.com/itm/326286798942?_trkparms=amclksrc%3DITM%26aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20211130125621%26meid%3D8d337d74bd3b42f28a787a537181d86e%26pid%3D101465%26rk%3D3%26rkt%3D4%26sd%3D186507266567%26itm%3D326286798942%26pmt%3D1%26noa%3D1%26pg%3D3814323&_trksid=p3814323.c101465.m3507)
not all 'cheap' kits are made the same, just be aware. those pistons def look different that the ones i run in the 72. :twocents:
Quote from: m in sc on April 09, 2025, 06:46:54 AMnot all 'cheap' kits are made the same, just be aware. those pistons def look different that the ones i run in the 72. :twocents:
You are not kidding! Well I am just getting online now. Fortunately or unfortunately I don't have to go to work till 1pm, late clamming tides so I have to time to mess with the bike. I just got the carbs installed this Morning and literally just fired up the bike for the first time. Doesn't sound good. A lot of rattling on idle speed and quiets down real quick with revs. I think it's coming from the left cylinder/fuel tap side. Just doesn't sound right. I know it sure as hell ain't my crank. Well I think it's those pistons/rings. I hope it didn't mess up the cylinders, ughh.
FWIW and I know it's hard to convey what's going on with my bike to all of you. Thank you for being helpful. Anyways I did liberally soak wrist pin bearings,pins and rings in two stroke oil and finger lubed the cylinders with the like. Primed the oil lines.I tried to be carefully seating the piston,rings as I guided the cylinders home but those rings just felt too loose like it was hard for em to stay put but I figures once everything was together nice and tight they would make a home. I just don't know, I'll have to take it back apart. Obviously.
Ok I probably should wait till after I get the cylinders off to type this but I just took the heads off and still in shock/disgust with myself...this. I hate to say it but it feels like both the connecting rods have play up and down. You can hear the rattling just kicking it over slowly and I can push on both pistons to feel the play,just gotta move em around on the right stroke. This sucks, well back to pulling it apart.
Maybe the piston skirts met the crank? Maybe some grit got in there in my haste to take it apart?,I don't see how that could mess up both connecting rod bearings.I dunno I was careful to keep it clean and make sure it was prior to reassembly. I will say the cylinder walls look Ok and the pistons don't seem to be binding up like the rings are ok. I don't know we'll see more later. Stay tuned.
so the heads on my 250 came off effortlessly, but the cylinders are a different story. any tips on how to free those up from the cases? i gently tapped at a few diff angles with a rubber mallet and also used gentle pressure with a wood pry bar between the cylinders but they are stuck pretty good.
attached pics of the 250 cylinders/heads/pistons, wonder if there is any info that can be gleaned from the condition of them? i still see cross hatching in the cylinders and the surfaces of everything look great. is there anything to look out for when purchasing used 350 heads, other than the obvious...not cracked, surfaces flat, generally clean?
i see some dry rot on the plug seals so i assume replacing all seals is the way to go. any suggestions for seal kits would be great, there are so many out there would like to get a set that people have had good luck with. related, is replacing all the seals a diy job or should i look to lean on somebody who's done it before? i am sure there is a thread here documenting changing seals but just curious how labor intensive it is.
and the cracked plastic trianglular thingy with the lead...that must be a neutral position sensor?
Assuming your engine isn't seized...I see the kicker still attached,did you try moving the pistons? Ask me how I know things can be stubborn to move :umm: Maybe the cylinders are just stuck to the gaskets and you gotta try exerting a bit more effort to pull of the cylinders?
I never tried pulling those transmission plugs either side of the off without splitting cases but I know it can be done. What's on the other side of them is the shafts that hold the gears,if they don't leak then I would leave em. You can get replacement plugs thru either Economy Cycles or HVC Cycles and they are easier to access if you split the cases but like I say if the don't leak just leave em. Yeah you are correct that white plastic triangle is the neutral sensor if the cracking is bad and bothers you then I imagine you may source one in better shape used on Ebay,Not sure if you can get that new? I would just call Economy Cycle or shoot em an Email and ask.
The seals to focus on are the crank seals and that shift shaft seal maybe nice to replace. Another maybe is thek seal where the crancase halves meet as well as the drive sprocket seal while it's apart.
Just my 2 cents.
Quote from: RDryan on April 09, 2025, 10:25:15 AMAssuming your engine isn't seized...I see the kicker still attached,did you try moving the pistons? Ask me how I know things can be stubborn to move :umm: Maybe the cylinders are just stuck to the gaskets and you gotta try exerting a bit more effort to pull of the cylinders?
i got the cylinders freed up this morn. i squirted a bit of penetrant into the stud recesses in the cylinder and 5 min later a gentle tap with the rubber mallet freed them both up. this motor ran tight when it last ran 35 years ago and turns over super smooth, so i have to think everything is in good shape inside but it will get a once over inside as well.
As far as the seals, none of them are leaking so it does fall into the aint broke don't fix it category i suppose but dry rot cracks on seals seem like a red flag that those are going to fail sooner rather than later. and as long as i'm doing all this work, doing the seals feels like the logical thing to do. the seal between the cases looks great and shows no signs of any leaks but if i want to have any idea of the condition of the lower end i'll have to get in there and have somebody who knows what they are doing take a look.
Quote from: mlakritz on April 09, 2025, 10:52:28 AMQuote from: RDryan on April 09, 2025, 10:25:15 AMAssuming your engine isn't seized...I see the kicker still attached,did you try moving the pistons? Ask me how I know things can be stubborn to move :umm: Maybe the cylinders are just stuck to the gaskets and you gotta try exerting a bit more effort to pull of the cylinders?
i got the cylinders freed up this morn. i squirted a bit of penetrant into the stud recesses in the cylinder and 5 min later a gentle tap with the rubber mallet freed them both up. this motor ran tight when it last ran 35 years ago and turns over super smooth, so i have to think everything is in good shape inside but it will get a once over inside as well.
As far as the seals, none of them are leaking so it does fall into the aint broke don't fix it category i suppose but dry rot cracks on seals seem like a red flag that those are going to fail sooner rather than later. and as long as i'm doing all this work, doing the seals feels like the logical thing to do. the seal between the cases looks great and shows no signs of any leaks but if i want to have any idea of the condition of the lower end i'll have to get in there and have somebody who knows what they are doing take a look.
Oh good, yeah you can send out what you need done to Either Economy Cycles(a forum sponsor) or HVC Cycles. I actually just got off the phone with HVC regarding my problem and they were super helpful. Again FWIW those two black plugs either side of the neutral switch are basically metal covered in rubber.
BTW here's a link to the neutral switch, HVC has the replacement part. https://hvccycle.net/neutral-switch-1l9-82540-00-00/?searchid=459451 (https://hvccycle.net/neutral-switch-1l9-82540-00-00/?searchid=459451)
They also offer a full suite of machine shop/engine build services, I know you mentioned that. I'm sure they don't mind if you wanna take the process as far as you feel comfortable and do a handoff so to speak in regards to rebuilding the bottom end.Or just take your time with it. I make mistakes and folks here on the forum have been helpful with me but I understand there is certain aspects of engine building that I won't venture into alone. So with these RD engines the cases do split really easy and the crank seals are pretty easy to replace. You really don't have to touch the transmission at all to do that just don't go much further with disassembly if that makes sense. You gotta take off the magneto,stator,generator and everything on the clutch side. and the cases are pretty much ready to split. I kinda forget a few special pullers and tools but they are available Thru either HVC or Economy. I will add that when I did take off all the necessary parts to split my cases the bottom end was still in the bike but that's not a requirement, I just didn't know any better way.
As an aside everything worked ok with my chinese cylinder kit but my problem is that six years ago I replaced the original 250 crank with a Vito's crank. Unbeknownst to me the Vito's has a beefier connecting rod and used a bigger set of wrist pin bearings. Hence the slapping I heard. So the OEM RD350 wrist pin bearing will not work in my case(O.D too small for the connecting rod end), I should have been more observant of this yesterday when I put it together.
I will also say that those Chinese cylinder were messed around with by HVC Cycles and I was told that they do have differences but there is a slight maybe they have gotten better quality wise. Something about softer metals used to make em. Slight variations in dimensions, just better to find the Yamaha ones even though they are rare and most of the time they will need to be bored out. I'm gonna order the bigger wrist pin bearings thru them as I am too far into the build to give up but even I am wondering if it's worth it. It's a chance to take.
yeah the vutos cranks use bigger diameter caged bearings but they don't contact pistons, or cases, period. I can't speak to 6-7 year old Chinese cyls but the ones I have run, that have been our for a few years are absolutely fine. I'm almost on year 3 on my set and I beat the r5 pretty good. Matt has a set in his 73, and my buddy travis had a set on his, I still have them and they wear just fine but they need to be prepped correctly, chamfer the ports, etc.
Quote from: m in sc on April 09, 2025, 12:07:19 PMyeah the vutos cranks use bigger diameter caged bearings but they don't contact pistons, or cases, period. I can't speak to 6-7 year old Chinese cyls but the ones I have run, that have been our for a few years are absolutely fine. I'm almost on year 3 on my set and I beat the r5 pretty good. Matt has a set in his 73, and my buddy travis had a set on his, I still have them and they wear just fine but they need to be prepped correctly, chamfer the ports, etc.
OK, I feel so stupid about this.I had the bike running on three or four tries for maybe thirty seconds total. Upon tearing it down I really can't see any noticeable damage or wear. Despite listening to the awful sounds of those pistons slapping.
I just ordered a set of two of them, was going to get em thru HVC but I found em on Ebay direct from Vito's at a much cheaper price between a 15% discount free shipping and buying as a set rather than individual. Sorry HVC if you're out there reading this, you are super helpful but I am just short on cash and tall on mistakes.
Can you expand on the chamfering of the ports? Is it just a bigger edge break than how they come as is?
Quote from: mlakritz on April 09, 2025, 10:52:28 AMi got the cylinders freed up this morn...
anything of note to comment on with the cylinders freshly removed?
(https://i.postimg.cc/3WHnF2xz/rd250-left-piston.jpg) (https://postimg.cc/3WHnF2xz)
(https://i.postimg.cc/yWXnQWJx/rd250-right-piston.jpg) (https://postimg.cc/yWXnQWJx)
the poet windows need to be radiused on cul a bit, no sharp edges. as far as that bottom end, aside from the muck and rust nothing stands out, just check the rod up and down play and side to side.
Quote from: m in sc on April 09, 2025, 04:06:52 PMthe poet windows need to be radiused on cul a bit, no sharp edges. as far as that bottom end, aside from the muck and rust nothing stands out, just check the rod up and down play and side to side.
so there is zero up and down play and a tiny bit side to side on each rod but i can't find my feeler gauge to measure accurately. it isn't much that's for sure, but not sure what the tolerances there should be or if there should be no side to side play at all.
do you have a manual? A lot of the spec stuff is covered in there. I never start motor tear down stuff without 1 -preferably a Yamaha branded 1. Makes life a lot easier.
RD250 & RD350 specs (this is from a tech bulletin for 1974 models)
Rod Clearance
Axial: New: 0.8-1.0; Max: 2.0
Side: Min: 0.1; Max: 0.3
yam_crank_rod_spec.png
Quote from: RDnuTZ on April 09, 2025, 07:09:39 PMdo you have a manual? A lot of the spec stuff is covered in there. I never start motor tear down stuff without 1 -preferably a Yamaha branded 1. Makes life a lot easier.
no manual but am finding stuff needed so far online. i'm gonna just buckle down and research stuff when i am unsure and when i really run into a dead end, i'll ask questions here. if i keep asking everything in my head right now this thread will stretch forever so i'll try to be judicious when posting. i'm just caught up in the excitement of the project at the moment.
Quote from: RDnuTZ on April 06, 2025, 10:43:07 PMyou need a stud removal tool like the 1 Mark recommended some time ago. I used to struggle with removing using Primitive Pete methods as well until I saw Mark's, so I went to NAPA and got 1 of these and they come out easy (using Blaster does help too)
https://www.jegs.com/i/JEGS/555/W83203/10002/-1?msclkid=1e0b40afb9fa13619be7275c8384e7d7&utm_source=bing&utm_medium=cpc&utm_campaign=WP_US_Bing_Shopping_555_Hybrid_Category_Catchall&utm_term=4581664973605614&utm_content=555%20Products
I used it multiple times on various sizes and it's great.
Ok, I did it! special thanks you as well as Striker and Mark. That tool kicks ass :clap: I actually got it over at a Advanced Auto Parts nearby with a Spring discount and unbeknownst to me my credit card's bonus pts. paid for it.
Didn't use any heat just the tool, Blaster juice and patience. The stud closet to the oil lines and grommet that got singed from heat was the toughest. Gave that one about half a dozen blasts and tapping it like the side of the can recommends over twenty minutes. Another stud gave an audible crack when it broke loose, felt like something satisfying when folks go to the chiropractor. Really quite amazed at how well intact the studs came out looking as well. Simply tightened the tool to as close to the bottom of the stud with out contact on the threads and it really didn't seem to mark up the stud at all. I thought for sure looking at those tools online that it would gall up the stud to the point of whatever, good forbid I snapped it...my worst fears were all for not. Nope every stud came off looking great for a potential reuse.
F'n awesome is all I can say,thanks fellas. Still waiting for the Vito's wrist pin bearings till then struggling with a cheap harbor freight dremel too I acquired recently to chamfer the poet windows. They came somewhat chamfered but not all the way around.
That tool is a huge work/time saver. Well worth what they cost :metal:
sweet! if you have a die grinder, I like to radius the ports with a small sanding drum (toostie roll) on a longer arbor. dremel can actually be trickier imho. 0.02
Quote from: m in sc on April 12, 2025, 01:42:35 PMsweet! if you have a die grinder, I like to radius the ports with a small sanding drum (toostie roll) on a longer arbor. dremel can actually be trickier imho. 0.02
Well I couldn't agree more about the Dremel being tricky. I got a very small one for under 10 bucks yesterday at harbor freight. I think it's a neat little tool and I thought it would be quite easy to work all around those ports at preferable 45 degree angles but it wasn't. Definitely takes some skill and careful hand and eye coordination. I unfortunately tagged the cylinder wall a couple of times. I was using a cone shaped stone and although I had just it as far out of the holding chuck as I could it just couldn't easily do the work right. Would be nice to be a longer arbor at least. I definitely would like to find a better tool.
I remind myself hey at least the tools and parts are cheap. I can afford the learning curve.
So question on these Kveldvulf cylinders...the flanges that sit in the lower case are not a tight fit into the case recess, you can see they are almost 2mm smaller diameter than the stock cylinders. This can't be right, is it? Looking at them from the bottom it looks like there should be a sleeve that slides right into the recess that makes it the correct fit but given this is my first time in an RD top end I have no idea. Maybe this doesn't matter? But it sure seems like something is amiss on the fit here.
are you sure you got them from the same seller?
mine fit very well 350 cyl to 350 cyl. comparison pic. the od of the sleeve is the same 250/350
Quote from: m in sc on April 13, 2025, 10:04:37 AMare you sure you got them from the same seller?
mine fit very well 350 cyl to 350 cyl. comparison pic. the od of the sleeve is the same 250/350
Well, same seller in terms of the link from one of the other users in this thread, I couldn't find a direct link in your old thread. But if you look at every listing on ebay now, they all look like they are cast like this. It is not unlikely that they all come from just one factory, many different seller accounts are obviously the same seller/distributor. So I'm not sure what to think. Is it possible that that groove facilitates oil flow from side to side of the cylinder? But how can you not have a positive fit/connection with that flange and the case, even if the studs are what ultimately dictate the position the cylinder?
there have been variations but from different sellers, i know this for a fact. there were indian ones and multiple chinese ones. i cant speak to yours directly. i have a set int he garage still new in the box, haven't even opened it. ill go open it in a bit and check them, they were bought recently just to have on hand.
Quote from: m in sc on April 13, 2025, 10:51:18 AMthere have been variations but from different sellers, i know this for a fact. there were indian ones and multiple chinese ones. i cant speak to yours directly. i have a set int he garage still new in the box, haven't even opened it. ill go open it in a bit and check them, they were bought recently just to have on hand.
I've sent a note to the seller, never know if that will be helpful but it can't hurt to ask. pic shows a rough measure the diff, 3mm+.
(https://i.postimg.cc/xkb7KF4m/rd-cylinder-OD-compare.jpg) (https://postimg.cc/xkb7KF4m)
interestingly, after checking amazon, there are a few nonsense name sellers (of course) who show a cylinder much more similar to the stock and ones in the older post. sleeve is still thinner but no outside groove. it's amazon, i'll probably just order a set and check them out and compare. But a lot of these listings have no reviews and are pretty fly by night sellers so I guess you just gotta shop around until you find one that seems right and decide if you want to buy cylinders from a store/factory that also sells baby nasal irrigators and beauty products :-)
https://www.amazon.com/360%E2%80%9111311%E2%80%9100%E2%80%9100-Performance-Shockproof-Aluminium-1973%E2%80%911975/dp/B0BY9S2H75 (https://www.amazon.com/360%E2%80%9111311%E2%80%9100%E2%80%9100-Performance-Shockproof-Aluminium-1973%E2%80%911975/dp/B0BY9S2H75)
just checked mine. yup there's a difference. also can say, there's never been an issue on my bike so me, i wouldnt sweat it. 0.02
If you are still looking for heads I have a pair of R5 high compression and high torque that CC'd at 20.5cc each, $100. plus ship. All fins and chambers are good. Outer fins need rubbed on and then fresh paint.
Quote from: m in sc on April 13, 2025, 12:26:54 PMjust checked mine. yup there's a difference. also can say, there's never been an issue on my bike so me, i wouldnt sweat it. 0.02
not sure if this is 100% accurate, but some research revealed that the thinner sleeve design was changed maybe starting in the early 80's in the Japan and Euro markets and that's what the current aftermarket cylinders are based off. not sure if it really matters, if it doesn't blow up or disintegrate then it's all good, right? I did order some amazon ones just to compare so we'll see what those look like and go from there.
mines been pretty abused and they are holding up fine for 2+ years, it gets shifted at 9- 10k a lot, the rev limiter is set to 10.5 on the cdi. it's an interesting point though. my guess would be more it was based off the Indian radjoot garbage cylinders. the real early ones had that porting and it was just dismal, so they def adjusted the sleeve layout to match the us spec ones. either way, good observation I didn't bother to make.
I just got those repo cylinders in my 75' RD250B and it runs good. Ran it approximately three separate occasions and rode about 15 miles between the 2nd and 3rd running in attempts. The first attempt was just running on the center stand for 10 minutes then I let it set and cool down for an hour. Not quite sure if I did that right with the"heat cycles" but it made sense.
Bike is good pretty much all stock except for the Vito's crank, Vape ignition and some Boysen reeds in the stock reed block.
Gotta get the jetting right but it fires right up and runs good.Too bad I had the wrong wrist pin bearings, my goof on that and also just a bit clumsy chamfering the ports. However I took advantage of the discount and ordered a second set of em just in case there's some demons going on with this install. Never hurts to have extra parts,albeit very cheap parts.
All great info, super helpful. Next question, anybody have any tricks for removing gaskets that have basically fused with the case? Pretty sure this is the factory clutch cover gasket on here, and I swear in some places it is hard to tell where the metal of the case ends and the gasket starts. How do i get that off of there without damaging the mating surfaces? Penetrant? Solvents? Razor blade? Once off, what is the best way to clean any residue off the case so it is ready for a fresh gasket? And then also just want to confirm that this tiny washer (see pics) that fell out when i pulled the clutch cover is from the kickstarter shaft? Eh, never mind, just found it on a schematic, confirmed it is the washer plate that slides on the kickstarter (the pic file name says shift shaft but it is the kickstarter shaft).
1st off, correct on the washer. that gets frequently lost. as far as removing the gasket material.. heat helps, scraping, cursing, etc IF you have air tools a die grinder or angle grinder w a green wheel with rubber fingers makes quick work of it. but, it also makes a mess. (rolock bristle pad)
Quote from: m in sc on April 22, 2025, 12:21:32 PM1st off, correct on the washer. that gets frequently lost. as far as removing the gasket material.. heat helps, scraping, cursing, etc IF you have air tools a die grinder or angle grinder w a green wheel with rubber fingers makes quick work of it. but, it also makes a mess. (rolock bristle pad)
softened the gasket with some adhesive remover and let it sit for an hour and came off pretty cleanly with a razor blade at a super shallow angle so as not to ding up the case. more adhesive remover took the rest of the residue off.
Anybody want to chime in on the pros/cons of decking 350 cylinders so you can use a 400 gasket? Some very reputable people (some on this forum) have suggested this as a way to go, and with no disrespect to them, just want to gather more info so I can decide if this is a mod I want to do and if the benefits are worth it and if there are any significant cons. I'm still going for reliability over pure power so curious what people think.
I have a set like that but tbh, I wouldn't go out of my way to do it
Ok, cases successfully split...so now what? :umm: It's unexpectedly clean inside and am unsure of what to do next or how to clean everything properly. Got a Vito's crank to install, and once the case is cleaned and ready to reassemble, I'd love to hear any insider tips and tricks to avoid any pitfalls or to make the assembly go smoothly. I've read on the forum about gaskets and seals and additional sealants or waxes to prevent leaks and stuff like that but would love any tips from the experienced so I have a successful reassembly. I have a tube of gray Yamahbond liquid gasket that I plan on using on the case mating surfaces, seems like that (or something very similar) was used at the factory, pretty sure this case had never been split before.
Quote from: mlakritz on April 24, 2025, 09:40:21 AMAnybody want to chime in on the pros/cons of decking 350 cylinders so you can use a 400 gasket? Some very reputable people (some on this forum) have suggested this as a way to go, and with no disrespect to them, just want to gather more info so I can decide if this is a mod I want to do and if the benefits are worth it and if there are any significant cons. I'm still going for reliability over pure power so curious what people think.
I've done this on a couple - it's a 5 minute job with a fly cutter on the mill. I like it as you can do it in conjunction with setting the squish. Worth noting that if you want to set the squish tighter than about 0.9mm, you want to pin the heads to the barrels so it stays consistent. I've done this with two bits of drill rod through both heads into the cooling fins on the barrels which is not the most accurate way but works very well. You take them out once you torque the heads on.
I'd buy 250 heads as they are way cheaper and pay someone to recut them - it's not a hard job and you get all the benefit of a real performance head for a fraction of the price. I've done them at 50/45/40% squish area and various CCs. I think 21cc would work on a stock(ish) bike, but I had to go larger on a ported engine and good pipes as it was detonating. Think I ended up at 23cc. Squish somewhere between 0.7mm and 0.9mm has always worked well. Stock is insanely large, like 2mm, so there's loads of room for improvement.
I've had a set of Kveldwulf cylinders up and running for a bit - they work great once cleaned up. Mine came honed quite large for some of the cast pistons but worked perfectly out the box for pro-x. Definitely measure first. I've never run the stock pistons they ship with.
If the main bearings feel silky smooth and are still covered in oil, I'd just change the oil seals (crankshaft and gearbox output shaft) and bung it back together with the yamabond. Give all the dogs in the gearbox a quick once over too. You could measure the run out on the crank if you feel like. I have had good luck with the new Taiwanese aircooled cranks you can find on ebay - the last one I bought was about 400bucks and insanely true. That said, it's still in the box as the current 250 crank that's in the engine keeps humming along smoothly.
Thanks for that info Jung, super helpful. I'm working through pros/cons of different options and think i've got a good plan moving forward. I got a set of performance 350 heads that won't require me to deck the cylinders and have squish and CC's right where they need to be for this project (mild street/midrange porting, CDI ignition, expansion chambers) according to a few tuners i've spoken with. I have a tube of YAMABOND 5, the drying liquid gasket as well as the Hondabond HT silicone liquid semi-dry gasket. I assume the semi-dry that stays more flexible is the better option for the cases? As far as the crank, the OEM one was out of tolerance on lateral play on the large bearing end so I got a Vito's to replace it.