question about compression

[not2hi]

On our 300ex, without the valve cover on (so the valves are not opening/closing)...should you be able to hear air leaking if you are turning the crank by hand? I would think that it should all be sealed and there should be no air leak...in fact i would think that you wouldn't be able to turn the crank by hand at all...correct?

I can hear air escaping - it sounds like its from down the cam chain pocket, but its very difficult to determine where exactly the leak is. Timing was dead nuts on, so I don't believe its a bent valve.

this is a Wiseco 11:1, btw...

background: recently rebuilt top end due to a possible head gasket failure. put everything back together, and it started on the first try (miracle!) ...ran for a few minutes, then wouldn't start...checked and compression was nil. Maybe a warped headO

[400exrider707]

If you had compression and lost it, you may have bent a valve. Probably what happened. I'd take the head off and inspect. Something is clearly wrong. There should be noice coming in and out of the cam chain area, that's the crankcase area below the piston, air moves in and out of there as the piston travels up and down, thus the need for the breather tubes on the cases. With the valve cover off however that would be the easiest path for escaping air.

[TheBlasterMan]

rings are not a perfect seal, especially when not warm.......

only info.....

[not2hi]

dang it...bent valve it is...just did a leak test.

so other than the timing being off (which I swear it was set perfectly before I started it, and it was still perfect after it stopped running)...what can cause a bent valve?

[GPracer2500]

Bad valve spring(s) or even the piston being in backwards could do it. Probably other things too but I can't think of any more.

Which valve bent? Was in only one?

[not2hi]

it was one of the two exhaust valves...

I guess a spring could be bad

stretched timing chain?

valves not adjusted properly?

[GPracer2500]

How old is this engine anyway? How did it run before it stopped? Did you decide on a reason as to why the head gasket blew? Was the engine pretty much stock before?


Timing chain? Valve adjustment? Maybe either of those things. Although if it was strictly a cam timing issue, it seems pairs of valves would have been damaged. If the cam kept one intake/exhaust valve in the clear, how did it not control the other? Maybe a stretched timing chain was only part of the problem. Whatever the case, a new cam chain and tensioner couldn't hurt. Same with valve springs. I mean--if the engine is low hour I'd probably only replace them if I was sure they are bad. But if they're old parts anyway...


On the valve adjust idea, seems like the engine would have run poorly (if at all) if a valve was so tight it was able to touch the piston. But anything is possible.


Is there a decomp mechanism on the cam? If there is and it acts upon the damaged valve valve, that'd be something to look at.


EDIT: I noticed you sig. With no rev limiter and a cam, at a minimum I'd measure those valve springs and be sure they're in spec. If you've run those springs hard, they're probably sacked out and that could have caused the contact you had.