How easy is it to bugger a valve?

So I had my cams out to start doing valve clearances... The crank must have turned while I had the cams out because when I put them back in and started rotating the engine to recheck clearances I heard the unmistakable clunk of valve on piston action.

So my question is... how likely is it that I've bent a valve?

I don't really want to pull the head just to inspect the valves, so I'm curious if anyone has any experience with bending valves. I don't have the cams back in so i haven't done any sort of compression test as of yet, just looking for advice.

As long as you stopped and reversed course when you heard it hit you could be alright if you were rotating it manually.
If both cams are out you could blow some compressed air down each splug plug hole and listen for it coming out intake or exhaust.
If you dinged it really good you might notice difference in bucket height in the bore

You can check out with compressed air. Piston at top, and put air in at the spark plug hole. See if it leaks out at the IN or EX valves.

You can check out with compressed air. Piston at top, and put air in at the spark plug hole. See if it leaks out at the IN or EX valves.

EDIT: Wiremans quicker.

It is really easy to bend a valve...turning over by hand can bend a valve, if the timing was altered. Now is the time to pull the head and check your valves. Attempt to set your valve clearances...if you have one or more valves that require much larger shims than others require, then it is possible that those valve(s) are bent (see wireman' post for an explanation of why a much larger shim might be required).

Do a leakdown test before you waste time pulling the head.

If you heard a clunk then you bent valves. It takes very little to bend them.

Ok, thanks for the tip on the bucket height, thats exactly the sort of thing I was looking for. I was turning by hand fairly slowly, BUT I was using the kick start lever so the engine speed can't have been all that slow...

I don't have an air compressor at my place, but I'll see about that tool that goes into the spark plug to test compression and I'll check the clearance.

I was really hoping to not have to pull the head and swap out valves but I'll see...

steell wrote: If you heard a clunk then you bent valves. It takes very little to bend them.

Ya I think you're right.

Easy, I did exactly the same thing 30 years ago. Ended up bending 3 valves- the one that hit the piston and the 2 that hit each other ( and you won't hear that). If your valve clearance is what it was when you started then you will be good, If its suddenly increased your not.

I'd already swapped the shims on the suspect valve so I can't be sure how big of a change, but it looks like it gained about 0.03 mm or therabouts. I turned the engine by hand though and looks like I'm pissing air out of that valve on the compression stroke... so ya...

@Roadflyer the cams were good in relation to eachother, just not in relation to the crank.

Never thought about it but can the piston top get damaged ever?

ah, well, going by the thread title i was going to suggest Vaseline but i see i got the wrong idea :huh: