What's the general consensus of piston to wall clearance for Pro-x pistons in an AC RD? There is no acutal spec as these are technically watercooled pistons. I've always used .002 for most rebores. Both Scott Clough and Garrett have done lots of boring for me and .002 was ok with them as well. Confirmed that again with Scott today. And Chuck Q has posted here saying .0019-.002 is fine as well.
I'm dealing with quite the shit storm on the air cooled UK forum with some of them insisting .002 is wrong causing piston slap and should be per the original Yamaha spec of .0015 and the've told my customer the same as well.
They diagnosed this from a cell phone video the customer posted, the bike had no cyl/head dampers.
And of course my customer now thinks his bike had a bad bore job thanks to them and is busy dragging me online in at least 2 forums in spite of the fact his bike runs great.
I've never ran away from these kinds of issue becuase I want to do the best job possible for my customers and if I'm wrong I'll man up and fix it for free, I just don't think I'm wrong and .002 is quite acceptable.
If there is slap there is too much clearance. .002" seems pretty well understood. I bet whomever did the bore read the paper with the pistons and did .003".
5port on that forum says he can determine clearance by ear to the 10 thousandths i.e. .002, .00175 .0015, etc. He said he listened to the video, determined the clearance was .002 but that is too much for prox pistons in an AC RD and is the reason there's piston slap (there isn't). He says the original yamaha spec of .0015 is the correct spec and at .002 there's piston slap.
I had someone tell me once (prob the same guy) that the 'rings in my motor were rattling and it was going to blow up'. this was on the lc topped bike... also by a cell video. :dawg: that topend was fine for 6 years until i blew the headgasket which was almost 8 years ago.
anyone that can 'hear a spec to the .0000 place' should stay off the forums and be busy saving the universe from Lex Luthor. :busey:
I used the prox spec. oem pistons are slightly thicker than the modern ones, so i spec it to the that due to the material composition and construction of the piston. the guy that has bored all my motors for years always uses the piston mfg specs and has never gotten one wrong IMHO.
https://www.pro-x.com/wp-content/uploads/2014/03/Piston-Kit-Instructions.pdf
Can tell clearance by ear to the nearest .0000? Really?
All except my prox top end from the 250 were loud. I attributed it to Wiseco pistons. Never really had a clearance issue.
John, maybe suggest your customer have a reputable, established shop/tuner/machinist pull his top end and make the call. If that party says the clearance is wrong, you pay the bill. If it's right, the customer is on the hook. :twocents:
Using pistons designed for a water cooled motor in an air cooled top end can be an interesting exercise. Let's talk about some of the differences. Air cooled top ends tend to run hotter so they need slightly more clearance than in a comparable water cooled top end.
On an RD that's ridden fairly hard without careful warm up, the chances of a 4 corners seizure rises significantly, so I tend to increase clearances a little on any ported motor.
The flip side of that is that when an AC motor is carefully warmed up it will tend to have a hotter barrel which in theory will run a little looser than a W/C.
So there are lots of variables. My take is that Chuck Q and Scott C both say .002 is good, then .002" is good. They are experts and know what they are doing. I get what the OP is saying about the change in noise as clearance increases and it's interesting and until he can document that, it's just another internet story. Stick to what the experts say and if they say 2 thou, then that's what I would use.
The internet unfortunately is a dangerous place where it's easy to harm someone's reputation.
Out of idle curiosity, are those "experts" in the UK or the US where running conditions tend to be very different?
I would guarantee its the UK.
fwiw.. having both ac and lc motors i've never seen a need of difference of spec using pro-x between the 2. Just haven't. But, to that point, then you would think the air-cooled bikes would require MORE clearance, right? :huh: their logic just doesn't hold up. and, the piston materials now is different than they were in 1974.
Seems like a headache that isn't necessary.
Quote from: Striker1423 on July 09, 2021, 10:27:01 AM
Seems like a headache that isn't necessary.
:clap: :bacon:
or.. fuck that guy. :omg:
I think any shop that is doing work for a customer is asking for trouble setting clearance at .0015. If that bike's timing or jetting is not quite right or gets run hard and hot, it could lock up and the rider end up on the ground. Then what would they post about the shop on the internet? Also, the sound in videos seem to make engine noises more pronounced than standing next to it listening.
Several years ago when we were racing (air cooled) TD3s and TR3 we had trouble sourcing TD and TR pistons but could find TZ (water cooled) pistons with the same exact bore sizes. I was concerned because there might be differences in the metal the pistons were cast from and asked Kevin Cameron about the situation. He told me the percentage of the metal in both pistons, silicon and aluminum, and they were different but he said that I shouldn't worry; run the TZ pistons in our air cooled bikes. He knew that we tended to run a bit on the rich side, as insurance, anyway but didn't think the mix meant anything. We did run the TZ pistons and had an occasional seizure but it was for other reasons, mostly brain dead tuners/riders. Of course these were OEM pistons, not aftermarket, so who knows about that.
As for determining piston clearance; I think I'd rather rely on my dial bore gage and micrometer than some idiots hearing.
Lyn Garland
teazer,
actually, its the other way round, the aircooled runs hotter, so the clearance can be less, as the barrel and the piston are expanding at roughly similar rates so the clearance remains predictable.
watercooled barrels run cooler so the piston expands more in comparison and reduces the clearance more, i believe that to be the reason that recommended clearances for water cooled pistons become debatable when the piston is going in an aircooled barrel.
even the above quoted pro x paper states that the manufacturers recommendation supercedes all of that information.
just my 2 euros worth.
les.
Quote from: m in sc on July 09, 2021, 10:14:11 AM
I would guarantee its the UK.
fwiw.. having both ac and lc motors i've never seen a need of difference of spec using pro-x between the 2. Just haven't. But, to that point, then you would think the air-cooled bikes would require MORE clearance, right? :huh: their logic just doesn't hold up. and, the piston materials now is different than they were in 1974.
Just to be clear, it's not based on logic.
Just to be clear.(https://uploads.tapatalk-cdn.com/20210709/5a7b3e8dc21e78d78ca8a28989313e93.jpg)
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The prox pistons are not oem as they were in the early 70's. they are different. therefore.... how would oem specs apply? they really don't, thats just material and construction differences. lc cyls temps are more stable and do run a bit cooler agreed. Aircooled cyls also will contract quicker than the more temperate LC cyls. Less thermal mass = (ac) quicker to expand AND contract.
I'll take the advice of these guys as well with modern pistons in mind, they are experts on this i would say....
https://www.lasleeve.com/downloads/piston-clearances.pdf
If they are Yamaha oem NOS pistons, different story. But not the case being discussed.
On all the bikes ive run, ive run these specs with prox and have never gotten a 4 corner seizure due to piston clearances. even when i ran the lc hot as hell a few weeks ago due to the timing it didn't hurt the skirts by expanding, but the domes were melted. Same with a few aircooleds over the years. Regardless, people can run whatever they want. I'm pretty sure since prox sells these for banshees, they are covering their asses with the 'use oem specs' and not for 50 year old aircooled bikes in mind. If they were.. they wouldn't have the tabs still on them.. .02
I agree with you, please don't think I'm not. I'm quite aware that the OEM clearance is not really achievable now, as it was in the day.
Just saying what was, back in the day.
If there is no reference to 'what was' then we have nothing to compare to.
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Oh, I didn't take it that way. And.. for the record, wasn't bashing on the brits (my best friend is British actually) at all but there are some obstinate fellows in that group.
My whole point for my (probably unnecessary) rant was to hopefully prevent somebody from locking up their motor.
(I'm looking at you Frank. :dawg: )
No worries.
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Quote from: elliottles1 on July 09, 2021, 12:02:56 PM
teazer,
actually, its the other way round, the aircooled runs hotter, so the clearance can be less, as the barrel and the piston are expanding at roughly similar rates so the clearance remains predictable.
watercooled barrels run cooler so the piston expands more in comparison and reduces the clearance more, i believe that to be the reason that recommended clearances for water cooled pistons become debatable when the piston is going in an aircooled barrel.
even the above quoted pro x paper states that the manufacturers recommendation supercedes all of that information.
just my 2 euros worth.
les.
Yes and no... Pistons and barrels expand at different rates and one reason is the ability to transfer heat from piston to barrel to cooling material (air/water) and more clearance usually means less heat transfer. I wasn't really trying to calculate the actual expansion rates but rather just drawing attention to the many factors (variables) that we can't effectively measure outside of an engine lab.
My refernece to the UK wasn't to put anyone down. It's just that thrashing a bike down a US freeway in summer is a very different thermal load that tooling around the average British road where temps tend to be lower and engines typically spend less time at high load. Lots of issues with those generalizations of course because that's the nature of anecdotes.
But point taken and lots of other relevant input.
I've had many cylinders done by a local shop and he uses .002 as well. Never had a problem. Not really sure how anyone can diagnose anything from a cell phone video. I think you should do just what Wade said and then tell the guy to shuv his phone up his ass and see if anyone can diagnose whats wrong with his brain.
How many freakin Prox pistons have been put in RD's? I'm gonna guess hundreds on this forum alone, if not thousands, and a lot of them probably had .002 clearance. Totally fine.
This guy can can hear a tenth clearance from a video?! :lol:
I remember Chuck harping many times on making the measurement on a piston for boring with any coating scrubbed off with Scotch Brite at the measurement spot. He was very adamant about it.
Do you think the spec sheet has the piston diameter recorded from measurements with the coating in place? I expect so.
RD's always sound a little like they have piston slap. It helps to put in the fin rubbers.
IR8D8R
Maybe he is a professional safe cracker.
This is simple. I would follow info from Clough & Quenzler as gospel. They are experts, they do this for a living, and have been doing it many years. Why argue with more than 80 years of collective experience? For someone to make an accurate analysis of bore clearance with an internet video is just ludicrous (especially with cylinder dampers missing). How many engines has this UK "expert" built and how many years has he been doing it? How many championship engines and how many land speed world records has he accounted for?
PS - I agree with Joe's comment above.
Quote from: SoCal250 on July 14, 2021, 12:46:30 PM
PS - I agree with Joe's comment above.
I've been waiting for someone to comment on that. :olaf:
Well, when you're right you're right :wink:
maybe he needs one of these?
Marc, if that's a "shit for brains" detector........................don't point it at me.....................D
Hi everyone - long time no see!
Some observations to consider; forged pistons 'grow' more than cast pistons. A loose top end is faster than a tight one - race motors are fastest right before they blow up from being worn out. Those little rubber buttons Yamaha put between the fins on the A/C 2T motors were to quiet piston slap and top end rattle, which are not necessarily bad noises. Don't worry as much if a top end makes some noise; when the noise goes away is the time to start worrying.
Warren
Thanks for all the comments.
This guy doesn't care how good it runs, he just cares how it sounds at idle. This all started with a rebore because he ran it out of oil. He installed the top end himself, we just bored and supplied pistons. He says we (Scott C)/EC) bored his cylinders incorrectly and supplied the wrong pistons, TKJR LC pistons.
And the bike came in with low top carb bodies with high top caps and slides. I put up a post about them a while back. So I swapped out the caps/slides for low top ones and now he says I stole his original high top carbs, never mind that the black paint on the caps was flaking but the carb bodies were obviously never painted.
The sad thing is his rd runs great now from idle to redline and is a nice original 75 other than low top carbs.
maybe send him a set of fin isolators and a cry towel.
Yup we installed the dampers. After we did the work he proceeded to send this video to "shops" in India for video diagnosis, and they all agreed with him its FUBAR. Here's his comment, the first paragraph of a 10 paragraph list of complaints accusing me of incompetence, theft, and a littany of other complaints. Maybe I'm old an my hearing ain't so good but it sounds like every other stock RD to me and it runs great, doesn't miss a beat to redline.
"1) When i got the cylinders back after a month+ long wait, I was shocked to see that i got the piston boxes with 350LC written on it and one piston feels looser than other when moved by hand when they are inside the cylinders. I was expecting that you would check with me before making a decision to install a Liquid Cooled pistons into an Air cooled engine. It is a well known fact that these pistons have different characteristics and it's not a best practice to install them in an aircooled engine and will cause issues. (Confirmed by repair shops in the RD business in India )"
wonder what he'd say about forged pistons with .003
And mind you he approved an estimate with TKJR pistons bored at .002, but appearantly didn't read it.
https://www.dotheton.com/data/video/112/112736-ac6a610c3e0a501bf18d1709277d5f25.mp4 (https://www.dotheton.com/data/video/112/112736-ac6a610c3e0a501bf18d1709277d5f25.mp4)
I've said this before. Not often, but have said it in person in a business situation:
"some customers aren't worth having"
don't let this fool sweat you, and if he ever comes back, just tell him to take his business elsewhere.
fuck that guy.
Mark pointed out that LA Sleeve recommends 2.5 thou or thereabouts for those pistons, so if the owner wants specific pistons and specific clearances it is his responsibility to clearly ask for that. If not he gets what the professional (you) recommends. That's why we use professionals.
If I want something machined a certain way it is my responsibility to communicate that clearly to the machinist and 100% my responsibility if they do what I ask them to do and it doesn't work. The OP doesn't actually know enough to know what he wants, but thinks he knows enough to be a critic. Touch of the old Dunning-Kruger effect there methinks.
Just to throw a money wrench into the mix, that RD does sound loud to me with my acoustically perfect (cheap) computer speakers and calibrated (not) ears. Is it possible that his big ends are a touch loose? Or is that just the effect of a cheap phone microphone? If he seized it when it ran out of oil, the big ends may be damaged. Just a thought. I expect to hear a higher pitched tapping/ringing sound with piston slap (clearance). On my PC that sounds deeper than I expected.
Either way, the OP is acting like a dick.
some digital cameras enhance those noises or what sounds like piston slap to a strange level. My fresh LC top-end on cell-ph camera sounds unbelievably awful. but.. its not.
Quote from: m in sc on July 28, 2021, 01:37:03 PM
I've said this before. Not often, but have said it in person in a business situation:
"some customers aren't worth having"
don't let this fool sweat you, and if he ever comes back, just tell him to take his business elsewhere.
fuck that guy.
+1
IMHO if he ever comes back just tell him to get his rebuild done in India! What a tool!
yeah and that's just it, I've explained to him that "piston rattle, piston slap and I think it sounds loud" are laymen's terms and aren't specifications especially from a video. I've owned a lot of RD's from brand new 1978 to every other incarnation stock and otherwise pretty sure I know how they should sound. The UK aircooled guys told him .002 is worn out. He didn't ask me to rebuild his engine, initially he just brought me the cyl's for boring/pistons. He then put it together himself and ran it then asked me to check it out because he thinks it doesn't sound right and something is terribly wrong. He then brought me the bike, fixed his Frankencarbs (low tops with high top slides/caps) ultrasonicaly cleaned his carbs, timed it and some other small stuff and install the dampers. I test rode it a lot, rode it home a couple times which I always do, then let it sit for couple days to make sure no leaks, then rode it again. It makes great compression and runs fine, really strong. He also listened to and rode my stock 400 which sounds the same.
There is no remedy for his problem anyway becuase you can't get Yamaha OEM RD pistons commercially anymore and bore the jugs to original Yam spec of .0015, so we're not going to rebore it and provide new pistons to be part of his "piston rattle" and "moved it with my fingers" and video diagnosis experiment.
You don't see customer complaints about EC becuase I just eat it if it's even questionable. I could and maybe should tell him what every other shop would, you put it together and ran it so don't blame us.
ID TELL HIM IF HE SUPPLIED OEM PISTONS YOU WOULD HAVE BORED IT TO THAT SPEC. BUT, ALAS.
John, it sounds to me like you've done absolutely everything you can and should for this fella. Letting him ride your personal bike is, in my opinion, going way above and beyond. Kudos to you, sir.
Here's one with oem pistons and the measurements were made with a bore gauge and a good quality micrometer. .0018 clearance on one piston and about .002 on the other. I used a Go Pro that was not in a case.
https://www.youtube.com/watch?v=AY64Vk0xVBc
Yup sounds like an RD. Sometimes I have to tell guys that just bought an RD that they are old unsophisticated motors with noisy clutches, points, vibrating fins, they smoke, are completely analog half century oid AC bikes, not new 2021 CB250's and the expectation can't be the same. It's easy to over think it if you're used to modern tech or your memory of them is decades old. If you "think" it sounds funny but it runs fine, then it's probably fine. And when there IS actually something wrong you'll definitely "know" becuase the noises will be awful, metal on metal, scraping, loss of power, soft seizing, failed bearings, rods, etc.
And when you blow by that new CB250 or throw a set of chambers on it and go KTM Duke 390 hunting (great bike no offense Mark think you have one), you'll love the way your RD sounds or won't care. They are easy to hot rod, easy to work on and you'll never get embarassed competing with modern bikes of similar displacement, and that's the reason we're all riding them, there's tons of parts, great forums etc, some half century after they were built.
And I tell them whatever you want to do to your RD has already been done, the body of knowledge is vast and it's one of the best vintage bike choices you could make!
had one.got rid of it for the CB1100
who knows what this guys goals was. however, with the aging group now into these things, we are def getting into the heavier priced but more frequent uneducated douchebag 1st timers that will blow thru this phase in a few yrs.
Quote from: m in sc on July 28, 2021, 05:23:50 PM
had one.got rid of it for the CB1100
who knows what this guys goals was. however, with the aging group now into these things, we are def getting into the heavier priced but more frequent uneducated douchebag 1st timers that will blow thru this phase in a few yrs.
Me withstanding of course lol.
I'm too into it now to give up. :toot:
Quote from: Striker1423 on July 28, 2021, 07:35:20 PM
Quote from: m in sc on July 28, 2021, 05:23:50 PM
had one.got rid of it for the CB1100
who knows what this guys goals was. however, with the aging group now into these things, we are def getting into the heavier priced but more frequent uneducated douchebag 1st timers that will blow thru this phase in a few yrs.
Me notwithstanding of course lol.
I'm too into it now to give up. :toot:
I wouldn't call you heavier priced, Striker... :Clown: