Valves kissed the piston!!!

Bike is a WR426f. I had a rock flip up and hit the waterpump cover and blew a hole in it without me noticing. 10 minutes later the bike seized. After ordering a new wiseco piston kit and resleeving the jug, I thought I was back in business. I have a hotcams exhaust and after timing it up with all the marks and putting it back together, it fired right up. I didn't let it idle for more than 10 seconds because it was late and I was tired. But it sounded fine. The next day I fired it up and it sounds like the valves are slapping hard. Really noisy. It starts up fine though. I figure the timing chain is stretched so I got a new one and got it installed. The bike is a bitch to start now and it still noisy as hell. A leak down test confirmed my suspicions, I was losing air bad through the intake. So I tore it down and this is what I found: Valves have nicked the piston. Where is the dumfounding part of it. What the hell would cause the valve to nick the piston like it has? Notice the mark on the right side of the right exhaust valve and also a nick on the left side of the center intake. It looks almost like the valves are aligned with where they should be on the piston? Any ideas?



I have Hotcams intake and exhaust, and I had a valve meet the piston. When I checked the cam timing with a degree wheel it was quite a bit off.

Maybe when your engine seized, the sudden shock of stopping caused the sprocket to slip on the cam. then when you rebuilt and set the timing by the marks, the lobes would not be synch'd properly. Is your cam sprocket adjustable or pressed on? Even pressed on it could slip. There was someone on here a few weeks ago with a stock cam sprocket that slipped.

Your hypothesis would work except that I had the stock manual decomp cam on when the engine seized. The hotcams was put on in the process of the top end rebuild. Here are my questions: Why does the piston have indentations for each valve? On TDC, how close are the valves to the piston?

One more thing I discovered that explains where on the piston the vavles hit: The piston in the cylinder can be rotated a tiny bit. Probably enough that a valve out of sync would hit it on the side of the valve indentation on the piston. No way in hell I am tearing into a bottom end to replace a crank. I don't have the patience or the skill. My last question before deciding to dump the bike for pennies or fix it: If I leave the crank as is, replace the topend valves and have the timing right, is there any reason why the valves would ever come close enough to the piston to kiss it whether it be on the shoulder of the valve indentations or in the center of them?


Firstly if the bike was running fine before you seized it , I would suggest the amount of movement in the big end is normal ( piston rotatation). Unless it ran out of oil and has done a bigend. This would allow the piston to come up too far hitting the valves.But doesn't sound like it.

Secondly you say the exhaust cam is different (new). It's possible that it is incorrectly timed. Which would result in the inlet cam being out of timming also. I''m talking timing dots. most unlikely though

Thirdly did the guy's who rechromed your cylinder grind the surface? If so reducing valve to piston clearance.

Wiseco pistons are widely used and this is the first time I've read that one has kissed the valves.

I would put my efforts into checking the valve train. That includes valve timming with a degree wheel.

If the cam lift of the new cam ,with it being higher, it would only account for the exhaust valves hitting not the inlet.

Good luck

You should not be able to rotate the piston at all. Either the big end or small end of the rod has issues.

Ya I figured the crank rod was beyond spec. Anybody care to elaborate at what point the valves are closest to the piston and how close? At TDC, the valves should all be closed. I understand that. The piston then fires and is sent to the bottom of the stroke where the exhaust valves open at some point. The question is how long do they remain open as the piston travels back up to the top of the stroke? are they slightly open as the piston hits the top or have they long since closed? Also, at the top of that stroke, I assume the intakes open up at some point drawing in fuel/air for the next ignition stroke. How close do they come to the piston if it is timed correctly? Thanks for the help guys. Awesome site.

Looking at your second pic, if the piston rotated counterclockwise under the valves, I can see that both those marks would have been made in those locations on the piston - not sure why any of the others would not have hit at the same time though, now here's another problem I see - the location of the piston in relation to your sleeve walls - it seems pushed to the right in pic 2 - normally, a piston with the rings properly seated around the ring locating pins doesn't sit off to one side like that, it naturally centers itself, is one of your ring pins tucked behind one of the rings forcing the ring out more that it should be thus offsetting the piston like that???

Wonder if that's the case and it's also what is making the piston turn counterclockwise on you like that.

Doesn't account for your timing issue, but it's a start to look for what might be causing the piston rotation other than a bad crank....

Matt, you might have opened a can of worms. Didn't use a manual on this one. I have done a couple of CRF topends with a manual and figured this couldn't be that much harder considering the wealth of info here on TT. That being said, what the hell are ring locating pins? Are they on the piston? I just offset the two compression ring ends from one another by 180 degrees. The oil ring ends were offset 120 degrees from each other

4 strokes do not usually have the locating pins. The only thing I can think of is that maybe you have the piston in backwards? Is the arrow pointing towards the exhaust side of the cylinder?

Ya, it is in correctly as far as intake/exhaust. Matt pointed out an interesting observation though. Why is the piston not centered in the cylinder? I guess I will pull it off and see ***. Keep ya updated

Never had my 4 stroke open that far, it just came to mind because my 8 yr old rebuilt his 65 this winter and it was one of the things I pointed out to him when he replaced the piston with a Wiseco. And yes, if it exists, it's in the piston where the ring slot is.

Keep us posted - maybe before ripping it all down, see if you can swing the piston back to the left (in pic) with your finger and see if it was an illusion first before going through all that trouble...

You can get the manual off the link in the stickies up top.

&$^%&!!! OOOOHHHH the agony of forgetting a circlip!!! The tiny mistake is going to cost me a new set of valves and piston. :applause:



Next and last question. I am assuming I don't need to recut the seats in the head? Do I need to replace all five valves or only the ones that fail the solvent test?

Thanks guys


I would replace all valves that you suspect have kissed the piston! if any doubt swap it out! a weaken valve may crack and have the head break off! you wanna talk about a catasrophic failure:cry: . I have had that happen to a truck I owned, turned the engine into a bucket of bolts. Be careful. Remove all the valves and roll them on a flat surface with the head of the valve over the edge and watch for it wobbling (sure sign its bent)

Ordered all 5. I guess the last question is do I need to recut valve seats?

I think that the seats should be alright unless you see physical damage to the seat. It would be hard to damage the seat without the valve breaking and a piece bouncing around for a while. I haven't seen a damaged seat with just bent valves and Ive been a licensed Tech for over 20yrs,maybe someone else has but not during my experience. Good Luck:thumbsup: dont forget to adjust the valves correctly

&$^%&!!! OOOOHHHH the agony of forgetting a circlip!!! The tiny mistake is going to cost me a new set of valves and piston.

Did you forget the clip or was it not fully seated, popped out, and is now floating around in the engine? If you are not sure, I'd remove some covers and look around in the bittom end.

The first thing you need to do is put a degree wheel on and check your valve timing to make sure nothing slipped. You have something wrong, either the piston has incorrect valve reliefs or valve timing is wrong. The piston looks suspect for having to small of diameter reliefs and if they did that, they probably didn't set the depth right.

Unfortunately you now have bent valves and need to get that fixed. If they are stainless they can be reground. I would not regrind titanium because you'll

take the nitrite off and they will wear real fast.

At top dead center of the exhaust stroke the intake valve is opening and the exhaust valve is closing. So yes, both valves are opened. How far open is relative to cam specs. You should have a minimum of .050 (imperial) valve to piston clearance for safe operation.

Bummer. I assume you have the errant circlip in hand and do not have to search the bottom end. I assume the bore is ok?

As others posted, replacing all five is cheap insurance. Seats will be fine.

Look at the bright side, you now have a fancy ashtray. Another positive is it was not the crank or rod.

I also hope you have the circlip in hand, else it's time to split the case.

I also hope that on pic 2 where the top of the crack is - that little triangle piece made it through to the sump and comes out with the oil change (I'd be draining into a clean container and then straining the oil to make sure) - it may not be big, but it can do damage.

By the looks of it, the wrist pin slid sideways and caught on the bottom lip of the bore and the force split the piston - any marks where it hit the bore? - it could leave a dent that protrudes into the bore some - you might have to have the bore refinished else it'll wear on the new piston.

Also, if that happened, it's like taking a sledge to the rod and bottom end, so inspect everything very carefully for excess free play or damage since your big end bearing could have taken a beating on that one hit.

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