how much does it take to bend a valve.. edit: guess I gopt lucky?

Well, in another post just recently I was talking about how my cam chain was liking to jump loose from the exhaust sproket when I was turning it over by hand. It was coming loose slightly and then when I would continue to turn it would pop back on.

Well one time it didn't, and then things got hard to turn so I stopped.

I recreated what I did (so basically I did it twice). This time I had a flashlight over a sparkplug hole and yes, the piston was coming into contact with the exhaust valve that had stopped closing on the exhaust stroke.

How can I know if I bent a valve, short of realizing it once I get the bike running (I guess I would know right away then?)

Post edited by: Trav, at: 2006/06/07 22:42

If it hit the piston i would be VERY surprized if it is not bent...not good.

Compression test will tell the tale

1045

This bike hasn't even run yet, I have no idea what the compression would be reguardless. Brand new wiseco big bore stuff.

I have to crank it over to pre-lube it anyway, might as well hook a compression gauge to it while that's happening.

Rings seated or not, I guess if I don't see that needle steadily rise, I know what happened..

I guess lady luck smiled on me..

100-120 psi on all cylinders, fresh cut valves and seats, big bore pistons and new rings. It has NOT been run yet (I hope to hell it's alot better at that point!)

Sounds like you're ok. You can tell right away if you bent a valve when you check your valve clearances. If any check way too high you know that valve is bent.

Well I've got my valve cover on and torqued down of course (to have cranked it over) but I checked the clearances both before and after the incident (I think). I know I checked them twice, once later when I had gotten the tensioner making the chain work properly, and they were all within a thousands or so of what my math said they should be with the new shims. I had bench checked them a few weeks back with the head off to see what I'd need.

One exhaust valve I remeber measureing at .010" when bench checking, and then the first time I did it today ont he bike it was .006". When I did them again later, it came out at .008", which was more acceptable, but still not the .010" I got with the head off. Then again, I didn't torque the cam caps when I bench checked the clearances. Probably should have, eh?

The clearances would be way higher because the valve would be bent and holding itself slightly open, correct?

It probably would be more that .002" and I probably wouldn't have gotten 120 psi compression either I guess.

Sorry for the long rambling post. I've done so much work on this thing in the past two days, and there are so many avenues for things to go wrong.

This is like sleeping with some chick with HIV and testing negative *WHEW* lol

Your on the right path, sounds like things are OK. Don't worry I went through the same things.

If a valve was bent and hanging open you would have significantly larger clearances.