Valves hitting top of piston

[Laverne Styre]

Hi everyone looking at buddys bike & we did tear down, pulled the head found valves had been hitting the top of piston not familiar with these as i am diesel cat mech. what is next step for repairs piston cylinder walls are in nice shape no damage still has crosshatch .?

[AlexCrf250r]

Are you sure the valves are actually hitting the piston? Is there a noise when your riding? If you just pulled the head to check up on the stuff chances are there not hitting the piston, 4 stroke pistons aren't flat so you will see indents of where the valves will go.

[Laverne Styre]

Yes the valves have been just slapping top of the piston as all the carbon has been knocked off the top of the piston ( all shinny ) perfectly round , just a guess but the carbon was was likely all the noise originally breaking loose when kid shut engine down.

[ForsheeMS]

Replace the piston, rings, and wrist pin. You will also need to replace the valve springs and inspect the valves, seats, and guides for wear and replace if needed. Valves hitting the piston are a sure sign that the valve springs have lost pressure and are floating. I would recommend a good quality aftermarket valves spring as the stock springs are a little questionable.

[chadk66]

Also make sure your cam sprocket hasn't spun. Also replace the cam chain.

[Laverne Styre]

Excellent feed back guys this is good i have already sent the head to nearest city 150 km away for inspection and rebuild, i will order all the other parts suggested by you fine fella,s as we are to far from a lot of places and we only want to do this once thanks a bunch aka.(coffin shot).

[Charlie C]

Double check the oil filter and make sure you have no metal in it. If you pull the filter and find that it has a bunch of brass looking meatl shavings, your crankshaft will need replaced. There has to be a reason why the valve and the piston met each other. A bent valve stuck in the guide or the bearing on the connecting rod could be bad also. Timing could also cause this condition, but rare unless the chain breaks or slipps. It is also possible like mentioned above that the valve springs are shot and floating. The springs are very inexpensive to replace and with any rebuild it is highly recommended.

[chadk66]

My money is on a spun cam sprocket. It happens very frequently.

[TDW]

My money is on a spun cam sprocket. It happens very frequently.

And when it does it is usually difficult to verify unless you know what the cam was initially set at, or if you have a cam card with the specs. and most guys dont have the tools and arent able to degree their cam.

The best thing to do is the first time you have the valve cover off, put marks across the hub end of the cam and cam sprocket, then if it ever moves its easy to see.

[chadk66]

And when it does it is usually difficult to verify unless you know what the cam was initially set at, or if you have a cam card with the specs. and most guys dont have the tools and arent able to degree their cam.

The best thing to do is the first time you have the valve cover off, put marks across the hub end of the cam and cam sprocket, then if it ever moves its easy to see.

exactly. I mark all my cams first time in.

[Charlie C]

My money is on a spun cam sprocket. It happens very frequently.

That's something I've never seen, but I certainly wouldn't rule it out! Nice tip!

[chadk66]

it's happened to me a couple times just in the past 6 months.

[ForsheeMS]

Normally when the cam sprocket spins it will retard the timing and only the exhaust valves hit. If that's the case I would look really close at the cam. If all 4 valves have hit you have a valve float issue.

it's happened to me a couple times just in the past 6 months.

You need to have the sprocket tack welded to the cam or replace it.

[chadk66]

Normally when the cam sprocket spins it will retard the timing and only the exhaust valves hit. If that's the case I would look really close at the cam. If all 4 valves have hit you have a valve float issue.

You need to have the sprocket tack welded to the cam or replace it.

this was on our kawi's. And it has been welded now.

[SLO_Rider]

Normally when the cam sprocket spins it will retard the timing and only the exhaust valves hit. If that's the case I would look really close at the cam. If all 4 valves have hit you have a valve float issue.

You need to have the sprocket tack welded to the cam or replace it.

Great tip! Are you just placing a tack or a small bead, just one or several? Also, mig, tig... does it matter? Happen to have a pic?

[ForsheeMS]

Are you just placing a tack or a small bead, just one or several? Also, mig, tig... does it matter? Happen to have a pic?

All you need is a small tack weld in one spot. Be sure to protect the cam bearings from any type of weld splatter as it only takes 1 little spot on the bearing and it's done. I usually wrap a shop rag tightly around both cam bearings to be safe.

[Laverne Styre]

I think that valves also might have been touching is, i did not mention was that the cam chain tension guides had been destroyed all the hard plastic melted and ground off. all the material ending up in the bottom & screen was full likely had to much slack in the chain ?

[chadk66]

I think that valves also might have been touching is, i did not mention was that the cam chain tension guides had been destroyed all the hard plastic melted and ground off. all the material ending up in the bottom & screen was full likely had to much slack in the chain ?

then it jumped time.

[Charlie C]

HMMMM. Timing could also cause this condition, but rare unless the chain breaks or slipps. Or of course the tensioner is shot or broke.

[Laverne Styre]

I have looked at the cam sprocket does not appear to have spun but i will put on a spot weld , thanks yes only the exhaust valves had hit the piston right on thanks again .