To put it simply, I don't have as much experience building two strokes, and I wanted to know what it would take to make my RD350 safe to rev a bit higher.
I have been told that the points get unhappy at 10krpm, and I have read a couple things about people having the cranks welded somehow to hold up better.
I basically want to get everything together for when I eventually do a total engine rebuild.
well.. lighter pistons, (vertex a good option) lighter ignition (would recommend HPI as its the smallest one). TBH, the cranks are OLD, the weights come loose at this age, even repressing them is a huge PIA and risky, i've had them come loose again. I run my vitos crank up past 10 all the time. it has a pork chop crank (no weights, its cut like a car crank sort of) and IMHO safer. also they coem with really good japanese bearings.
another option is to change the primary gear to a 250 style. that means 250 clutch/primary/oil pump (if you are on the pump). this actually reduces the speed of the clutch and transmission overall, reduces windage drag, and the gearing can be 'made up' on the front chain sprocket :twocents:
Quote from: m in sc on July 21, 2025, 09:38:39 PMwell.. lighter pistons, (vertex a good option) lighter ignition (would recommend HPI as its the smallest one). TBH, the cranks are OLD, the weights come loose at this age, even repressing them is a huge PIA and risky, i've had them come loose again. I run my vitos crank up past 10 all the time. it has a pork chop crank (no weights, its cut like a car crank sort of) and IMHO safer. also they coem with really good japanese bearings.
another option is to change the primary gear to a 250 style. that means 250 clutch/primary/oil pump (if you are on the pump). this actually reduces the speed of the clutch and transmission overall, reduces windage drag, and the gearing can be 'made up' on the front chain sprocket :twocents:
I had seen the vito's, and wondered if it was better. Thats good to know. I had also never heard that about the other primary gearing from the 250 until now, and yes I run an oil pump. How hard is it to source those pieces these days?
not sure. probably pretty easy via ebay. you have to run a 250 pump though, the internal gearing is different. YES it will feed a 350 motor just fine, been there done it (on an lc conversion as well).
the only issue might be the 350 basket set up for a 6 disc clutch vs 7, but the replacement baskets they sell are 7 disc compatible and can be retro fit onto a 250 clutch gear.
How crucial is the 250 setup? I don't plan to beat on mine constantly, and am not trying to squeeze every bit of horsepower possible out.
not crucial at all, not required. just an option
What pipes do you have?
That will also be a factor.
To go further on this. Is there a reason you shouldn't weld an OEM crank Vs buying a Vitos? If those are the only 2 choices and you really want to spin it. Since we already know that old stock cranks may come apart after so many repeated trips above 10k? Sure you may not be able to build it again. You can grind out a weld if it isn't just blasted solid. Or buy the aftermarket next time you need bearings.
It only takes a tack weld or do you need to really lay a deep bead on it?
IR8D8R
Quote from: JKV45 on July 24, 2025, 09:10:20 AMWhat pipes do you have?
That will also be a factor.
Wicked motorsports
because stock cranks can and do have the weights come loose. i have a really nice welded crank that has maybe 2k on it (tig welded, its out of my white lc hybrid) that the weights came loose and started tapping the rod. not worth it to me, and i build my own cranks. yes, i even pressed the weight back in on the rebuild. and sorry, the current vitos cranks are just better quality overall.
fwiw, I bought 1 Vitos and 2 from HPR on eBay. Have not installed any yet, but visual inspection shows top notch quality on both. Vitos uses the KOYO Japan crank bearings IIRC and HPR uses TPI Taiwan bearings. The HPRs are a bit cheaper at listed price, but I had Vitos on my watch list for months and they eventually sent me an offer for 10% off. HPR lists both a 250 pn compatible and a 350 pn compatible. I bought 1 of each and both came with wrist pin bearing for 350 so confirm whatever you will get either way you go.
https://www.ebay.com/itm/364763626092?
Quote from: Vintagewannabe on July 25, 2025, 05:17:43 PMQuote from: JKV45 on July 24, 2025, 09:10:20 AMWhat pipes do you have?
That will also be a factor.
Wicked motorsports
Can you get a dyno chart from them to see what the powerband looks like and at what RPM they taper off?
You would want to make sure they were capable of the revs you are going for.
Quote from: JKV45 on July 28, 2025, 10:01:55 AMQuote from: Vintagewannabe on July 25, 2025, 05:17:43 PMQuote from: JKV45 on July 24, 2025, 09:10:20 AMWhat pipes do you have?
That will also be a factor.
Wicked motorsports
Can you get a dyno chart from them to see what the powerband looks like and at what RPM they taper off?
You would want to make sure they were capable of the revs you are going for.
wicked_pipes_dyno_rd350.png
wicked_pipes_dyno_rd400.png
Just an aside: DS7/RD/R5 cranks are virtually identical to TZ250/350/750 cranks. TZ cranks live 90% of the time WFO above 10K, put out about twice the HP of an RD, and don't come apart or twist unless rebuilt many-many times ... and it's still a rare occurrence. A rebuilder can tell by the tons of pressure required and the 'feel' splitting and assembling if the pin-fit is too loose; Yamacranks are amazingly reliable as is.
RZ cranks are a different story - they tend to spread apart 'more than twist.' I've seen a couple spread enough to bind up the motor; usually it's the timing-side flywheel that comes adrift.
Myself and virtually every TZ racer/rebuilder puts the pox on crank welding; never have, never will.
Warren
I agree. but they also don't see the run time a street bike sees. my r5 crank made it 27k before it started to spread to where it was an issue, but the weights were fine. bu also a low rpm motor. imho comparing short high rpm use race bike cranks to street bike cranks are apples and oranges.
Quote from: SoCal250 on July 28, 2025, 12:41:55 PMQuote from: JKV45 on July 28, 2025, 10:01:55 AMQuote from: Vintagewannabe on July 25, 2025, 05:17:43 PMQuote from: JKV45 on July 24, 2025, 09:10:20 AMWhat pipes do you have?
That will also be a factor.
Wicked motorsports
Can you get a dyno chart from them to see what the powerband looks like and at what RPM they taper off?
You would want to make sure they were capable of the revs you are going for.
wicked_pipes_dyno_rd350.png
wicked_pipes_dyno_rd400.png
I appreciate someone helping by posting the charts, and it feels like the bike is still pulling at 10k.
Just to be clear on what I am trying to do personally; The bike is at about 22k miles on as far as I know stock bore and fairly certain stock bottom end. I want to start gathering parts for a rebuild in the next year or so, and since I am rebuilding it I want to improve some. It is still very much a road bike, and while I love being aggressive on curves, I don't want to build a monster that isn't fun to ride around town anymore. RDnuTZ, thats some really good info, hadn't really even realized there were other popular aftermarket cranks.
This is exactly the info I was hoping to get together in a thread
more than likely its not really pulling past 9. I have ported motors with corrected heads, etc, can rev to the moon.. and i have the rev limiters on the ignitions set to 10.2 because of over rev, to shift at 9200-9500. thats where peak power usually sits. Be skeptical on relying on stock tachs to give you correct rpm readings at speed. they can be incorrect in either direction. my 72 r5 w rd motor was reading (jumping) too high and thats why i went with an aftermarket tach, and the 70 r5 (which is dead stock) reads too low , but thats fine on that one. a temporary digital tach on a ride will usually reveal where the motor really is. 0.02
QuoteI agree. but they also don't see the run time a street bike sees. my r5 crank made it 27k before it started to spread to where it was an issue, but the weights were fine. bu also a low rpm motor. imho comparing short high rpm use race bike cranks to street bike cranks are apples and oranges.
Considering that a lot of Factory R&D is gleaned from (private and works combined) race efforts, discounting comparative analysis between race and street may not be entirely accurate. Working at a race-shop/Yamaha-dealer (CycleSprings Yamaha in Tarpon Springs Florida) during the 'RD' years was most enlightening; the factory rep 'Bud Parker' had his nose in a lot of the race (and street) bike motors, and since this was the heyday of 2T competition motors CSY was a frequent stop.
I remember Daytona very well, the most motor-eatingest track there is; I raced an RD400, an SR500, and an XS11 there for several years back around 1980, and believe me, there is nothing compared to the high-rpm use any bike gets there; it's a lonnggg way around the high banking - WFO and 10K for 2.5 miles straight, then repeat again and again.
Hatched the RD400 twice and the XS11 one time at Daytona - the RD seized once, then holed a piston next time (both times on the 'banking); the seizure was bad enough that it ovaled the rod and I had to rebuild the crank - the rest was fine (10K motor with probably 1K race miles). The XS11 was a catastrophic engine failure - it broke on lap 57 in a 250-mile endurance race (the Paul Revere 250); 5th wheel gear was bushed instead of having a roller-bearing and locked tight on the shaft at 140MPH+, breaking the engine case and turning the gearbox into scrap-metal. Bud P. was most interested in that failure and since I was not the only one - a Yamaha Service Bulletin followed.
Ther main reason I posted about race cranks was to certify the reliability and strength of the stock Yamaha's. I have only lived with Hoeckle aftermarket RD/TZ cranks so cannot comment on others beyond rebuilding them, but I swear by, and not at stockers; virtually any amount can be spent building motors and that is much of the fun with the RD platform, but vast improvements to bottom-ends are expensive and not entirely necessary endeavors.
Warren
PS, my rod of choice is the Yamaha 34X - went in all the 250, 350, and 750 race motors (and a few street RDs) I've built with zero failures or issues. Racing is a true test of cranks, especially at high RPM. One possible mod to the RD might be converting to Yamaha H/D Flat-Roller drive-side main - much stronger than the ball bearing.
OK, the pics are a TR2 race motor, but the effects are the same:
no disrespect, but that was 45 years ago tech. metal changes with age, as does technology. there's a reason yamaha changed the design of the cranks on the the rz, lc and tzr.etc.. etc.. the vitos crank is of that same design. reality is race spec and street spec parts are different for a reason. 50 years of street use takes its toll. Aside from being pretty well versed in crank and engine building, I'm also a mechanical engineer. we can disagree but times have changed on what's available for these street motors. while a race crank can def take a harder beating , the beating a stock crank takes overmuch more time... even at moderate rpm levels takes a toll of a different kind. its not a pissing match, just 2 different applications . but having rebuild my share of rd and triple cranks, ill never bother rebuilding a 250 or 350 crank again. ill just replace it. aftermarket can, on occasion, exceed oem quality. 2 examples of this are cdis and these cranks. Just my opinion.
m in sc, you missed my point.
quote: Ther main reason I posted about race cranks was to certify the reliability and strength of the stock Yamaha's.
that's the point I read. and I agree with tgqt.. if the crank isnt 40 yrs old. not being argumentative.