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Cylinder/piston issues....

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First let me say this is a long post/rant but I've had more issues with this one bike than all my previous ones combined and I hardly ride this thing

Things to note: 100 octane fuel mixed at 32:1 with Castor 927. Bike has been jetted fat ever since I switched to the 100LL, still in the process of dialing it in. People who've watched my helmet cam videos say the bike sounds healthy if that means anything lol

Today I pulled the topend apart because the gasket between the reed cage and cylinder was weeping oil. No air leak, bike ran great, was a tad rich but I didn't feel comfortable with a gasket I thought be prone to leaking eventually. I used a ProX gasket kit when I built it and they seemed crappy so I decided to pull the whole topend apart to replace them with ones I've had good luck with. I have two rides on the bike since I built it with a Wiseco single ring 808 YZ piston ($$$). You may have read my thread during the summer when I replaced a piston with a stuck ring. The bike must have got hot but not enough to seize; it still ran great but it was due for a topend. The cylinder looked fine though, absolutely no scratches or anything out of the ordinary.

My essentially brand new piston is scored right where the piston passes over the right side powervalve "bridge." I can feel it with my finger nail very easily, the rest of the piston looks new. The cylinder is smooth but has visible wear on both bridges on either side of the powervalve. I was surprised to see any damage since it ran fine. I have seized a bike so I definitely know how that goes. It can't be a cold seize, I warm up my bikes for a long time and have run Wiseco pistons since I raced 85s.

IMG_1690.JPG

This is what I'm talking about, kickstarter side side of the piston. The left side of the piston has this to a much less degree. Partial four corner seize? Well maybe a 2 corner seize but it definitely wasn't due to being lean or not warmed up.

IMG_1678.JPG

The scoring on the piston lines up with this. That right-side powervalve looks like it protrudes into the cylinder awfully far... Thoughts?

IMG_1679.JPG

Other side. This valve looks much more ideal.

IMG_1681.JPG

Intake side, this looks rougher in the picture than it does in person, its perfect smooth, cross hatching is still all visible.

Any ideas what might cause these symptoms? I have ran tons of Wiseco pistons and never had this happen. Would this happen if the piston slightly too large? Power valve clearance too small? Cylinder out of round? I'm kind of thinking I screwed up by not having my cylinder inspected when I found the stuck ring but that doesn't explain why the piston I pulled out this summer wasn't scored at all. The bike has never legitimately overheated or seized. In fact I was surprised when the last piston had a stuck ring because it still hauled ass.

I probably rode it less than 5 times during 2011 to give you an idea. This is the first time I've seen significant wear upon inspecting a piston.

Thanks for any help :smirk:

Ryne

Edited by MotoXRyne

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the plating on that cylinder looks worn, i'd say get a replate to true that cylinder back up, that damage is either from too tight there, or a piece of debris. one other thing, that piston should be drilled at the bridge, this keeps that hot area cool and lubed, the instructions w/ it explains where to drill it, and also the weisco website has the info.

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the plating on that cylinder looks worn, i'd say get a replate to true that cylinder back up, that damage is either from too tight there, or a piece of debris. one other thing, that piston should be drilled at the bridge, this keeps that hot area cool and lubed, the instructions w/ it explains where to drill it, and also the weisco website has the info.

07 doesn't have a center exhaust bridge. OEM piston didn't have any holes on the exhaust side, should I be drilling it for the bridges in between the main exhaust port and the side ports?

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07 doesn't have a center exhaust bridge. OEM piston didn't have any holes on the exhaust side, should I be drilling it for the bridges in between the main exhaust port and the side ports?
that's a good point, seems to me those webs between the ports are the same as a center bridge, and thats where your problem is, its still a bridged exhaust port, and add to the fact of high octane fuel causing more heat, i'd drill it, the reason the oem isn't drilled is, it's cast and expands at a different rate then a forged piston. to really tighten that up, i'd plate it also, it makes a big difference in compression, especially w/ a 1 ring piston, my cylinder is holding 165 psi, for about 60 hrs, w/ just ring changes every 15 to 20 hrs, on the same piston.

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07 doesn't have a center exhaust bridge. OEM piston didn't have any holes on the exhaust side, should I be drilling it for the bridges in between the main exhaust port and the side ports?

No need to drill the piston on an 07.

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and add to the fact of high octane fuel causing more heat[/b], i'd drill it, the reason the oem isn't drilled is, it's cast and expands at a different rate then a forged piston. to really tighten that up, i'd plate it also, it makes a big difference in compression, especially w/ a 1 ring piston, my cylinder is holding 165 psi, for about 60 hrs, w/ just ring changes every 15 to 20 hrs, on the same piston.

High octane does not cause more heat, it is the same. Octane is just a measurement of fuels ability to not predetonate.

You only drill pistons with a bridged exhaust port.

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Your right hand powervalve does not look right. That is your issue.

I've thought it looked strange ever since I pulled it apart to do the first top end a couple years ago but it never caused any damage. How would I go about fixing that powervalve so it doesn't happen again? Also there is also scuffing on the left side of the piston too, although it is not nearly as bad as the right side.

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I wonder if you measured the bore it would be a little worn? Your bike is essentially a brand new bike but you never know how good the plating was from the factory.

As far as the powervalve goes you've never taken it apart right?

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Have you messed with the stator timing since the last piston was changed out? Have you milled or change anything with the head? If so, then that maybe your new heat. Those are heat score marks on the piston and cylinder. I would drill the piston in those areas if it was mine. Also look at the 2nd photo and it looks like a flake has came off on the right power valve hole. I would chaffer the port on both the right and left.

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I wonder if you measured the bore it would be a little worn? Your bike is essentially a brand new bike but you never know how good the plating was from the factory.

As far as the powervalve goes you've never taken it apart right?

I've taken the powervalve apart twice for the last two topends I've done. That ride side power valve has looked like that since I first got the bike and I know I put it back together correctly because the bike runs great. I would measure it if I had the tools, none of mine are sensitive enough for that. I need to take it somewhere.

Have you messed with the stator timing since the last piston was changed out? Have you milled or change anything with the head? If so, then that maybe your new heat. Those are heat score marks on the piston and cylinder. I would drill the piston in those areas if it was mine. Also look at the 2nd photo and it looks like a flake has came off on the right power valve hole. I would chaffer the port on both the right and left.

Everything about the motor is stock besides the piston and reeds. In the second picture I think you're referring to lower left corner of the right exhaust port. It looks like that because it seems the power valve protrudes too far into the cylinder, it has been that way since new.

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It might be worth your while having a read of this very lengthy thread, as it relates to a similar problem (with a very similar looking bore photo) and involves a newish Wiseco piston too.

http://forums.mxtrax.co.uk/showthread.php?t=316870

That's my post :smirk: still unconfirmed what caused it. Looks like the big end is worn, causing the piston to wear badly in just 3 hours

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That's my post :smirk: still unconfirmed what caused it. Looks like the big end is worn, causing the piston to wear badly in just 3 hours

I have probably 2-3 hours on this topend. Two trips to the track for practice. Unlike your case, my bike ran great during my last ride. The only reason I took it apart was to replace a ProX gasket kit since I didn't feel comfortable with them. They seemed cheap. Really didn't expect to find anything wrong with the piston though. I haven't changed one thing in the motor besides swapping a Wiseco Prolite for a single ring Racers Choice piston. That right side exhaust valve has looked that way since I bought the bike new. Never thought it was an issue since I've had no problems until now.

Do the black marks on the cylinder between the exhaust ports indicate the plating is worn off or what?

I think what I'm going to do it put in one of the pistons I pulled out when doing a previous topend rebuild. None of the topends in my bike went many hours before I replaced them so it's not like I'm putting in a piston that's ready to fail. I'll run one for a couple rides and then tear it down to see what it looks like inside.

Pics after I gave it a good cleaning and scrub with a scotchbrite pad.

IMG_1704.JPG

That notch in the lower left of the port is there because the exhaust valve protrudes that close to the edge of the port.

IMG_1705.JPG

Other side

IMG_1706.JPG

This is the piston I pulled out over the summer. Top ring is fine. Bottom ring is stuck, definitely looks like it got hot. Underside of piston is black. But there is no scuffing that I can feel with my finger nail anywhere on the skirt.

Edited by MotoXRyne

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Got some more input based on your old piston, your are leaking down some brutal heat to melt that ring in like that, and its coming from leakage past the rings, so i'm still stuck on doing a replate, your cylinder is worn, no doubt, have you ever taken a compression reading? i'm willing to bet it's low, also you are somewhat lean on jetting, that combined w/ a leaky cylinder is causing that type of damage, i know you said it runs great, but i think those are your answers.

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Got some more input based on your old piston, your are leaking down some brutal heat to melt that ring in like that, and its coming from leakage past the rings, so i'm still stuck on doing a replate, your cylinder is worn, no doubt, have you ever taken a compression reading? i'm willing to bet it's low, also you are somewhat lean on jetting, that combined w/ a leaky cylinder is causing that type of damage, i know you said it runs great, but i think those are your answers.

It may have been a tad lean when running that old piston compounded with the fact that the last time I rode on that piston was on a sand-ish track in the 110F heat. It definitely wasn't lean after the rebuild, I bumped the main and pilot up a size and it blubbered around the track. Dropped the main and pilot back down and it runs much better, still a tad fat on top. I'm going to try and stop by Jerry Hall's shop and see if he can give me some insight on the cylinder. I think you may be right about the plating being worn though, just hard to believe that it is with as little ride time as this bike actually gets. I don't know what the compression is, I haven't tested it since I did the first top end and I don't remember what it was then.

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It may have been a tad lean when running that old piston compounded with the fact that the last time I rode on that piston was on a sand-ish track in the 110F heat. It definitely wasn't lean after the rebuild, I bumped the main and pilot up a size and it blubbered around the track. Dropped the main and pilot back down and it runs much better, still a tad fat on top. I'm going to try and stop by Jerry Hall's shop and see if he can give me some insight on the cylinder. I think you may be right about the plating being worn though, just hard to believe that it is with as little ride time as this bike actually gets.
do you think it has 100hrs on it yet? (btw get an hourmeter, it really helps!!) seems like that's about all the plating is good for. personally, i'd cut the 100 fuel down some, maybe 70% pump gas, 30% race fuel, 2 strokes really aren't big on high octanes, they need more of a slow burn to make power. i think 94 or so is the most thats needed, that high octane just burns so quick and hot and really doesn't give a nice long push on the piston,not to mention the amount of heat for that quick explosion, plus your hot ambient temps in AZ. just my opinion, i am a mechanic for a living, so i've seen alot of engine guts over the years.:smirk:

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do you think it has 100hrs on it yet? (btw get an hourmeter, it really helps!!) seems like that's about all the plating is good for. personally, i'd cut the 100 fuel down some, maybe 70% pump gas, 30% race fuel, 2 strokes really aren't big on high octanes, they need more of a slow burn to make power. i think 94 or so is the most thats needed, that high octane just burns so quick and hot and really doesn't give a nice long push on the piston,not to mention the amount of heat for that quick explosion, plus your hot ambient temps in AZ. just my opinion, i am a mechanic for a living, so i've seen alot of engine guts over the years.:smirk:

I'd say it has 50 hours, at the most, and I feel like that is a gross over estimation. I rode the bike 4 times that I can remember in 2011, not much more in 2010. Most of the riding was done between the time I bought the bike in May 08 and end of 09. I always ride at the track and maybe put an hour of ride time on it each time I go.

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I'd say it has 50 hours, at the most, and I feel like that is a gross over estimation. I rode the bike 4 times that I can remember in 2011, not much more in 2010. Most of the riding was done between the time I bought the bike in May 08 and end of 09. I always ride at the track and maybe put an hour of ride time on it each time I go.
you bought it new i assume? so ok, you guess about 50 hrs, well your plating probally is 1/2 worn, just guessing, i found if it starts to look real shiney like chrome, in places, and is kind of blotchy looking, especially around the middle of the cylinder, thats the signs of plating wear. it's really a performance enhancer getting a replate, the cylinder is perfect size, like new, and it really creates a good ring seal, a cylinder mic is also a way to check it, an engine shop can check it. one other question. did you just start using the race fuel on that old piston? i hate to bash your fuel, but i'm thinking its part of the problem. thats all. i'm just trying to get the right answers for you.

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you bought it new i assume? so ok, you guess about 50 hrs, well your plating probally is 1/2 worn, just guessing, i found if it starts to look real shiney like chrome, in places, and is kind of blotchy looking, especially around the middle of the cylinder, thats the signs of plating wear. it's really a performance enhancer getting a replate, the cylinder is perfect size, like new, and it really creates a good ring seal, a cylinder mic is also a way to check it, an engine shop can check it. one other question. did you just start using the race fuel on that old piston? i hate to bash your fuel, but i'm thinking its part of the problem. thats all. i'm just trying to get the right answers for you.

Yeah I bought it new. I started using the 100LL when I put this new piston in because the piston I pulled out had some evidence of detonation. I ran the bike on 100LL a few times on the stock top end and that piston looked great when I pulled it out. I also ran the same fuel in my mod CR85s when I was younger and no issues either.

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