Compression gone in one cylinder
 

I have a pair of 468's with 781 heads that were suppose to have all the necessary work done to accept stainless valves. These are newly reman'd engines w/ 5 hours tops. Just running trying to get them broke in well and started getting smoke in the cockpit all of a sudden. I had already ran them 2-3 hours at the lake on two seperate days and everything went perfect. Took it back and I have smoke coming back through the crankcase vents. Checked compression and #3 doesn't have very much at all. You can hear the compression coming back up through the crankcase with the vents out. Using no oil and no water leaks. No water in the oil and no smoke out the exhaust.

Is there anything it could be except a valve toasted, bent or otherwise crapped out. If the rings didn't seat there still wouldn't be crankcase pressure and there would be smoke out the exhaust, right? If the head gasket blew there would be water/oil leaking somewhere. I just want to hear any other opinions before I get on the phone with the guys that built the motors.

Thanks in Advance!

Re: Compression gone in one cylinder
 

I think I would be making that phone call right now...

Re: Compression gone in one cylinder
 

doesn't really matter since its going to come apart anyway... but sounds more like a piston/ring issue. bad valve isn't going to give you crank case pressure....

Re: Compression gone in one cylinder
 

Just melted two pistons. Same symtoms as you. Mine was from running too lean at wot.

I just found out my knock sensor was bad. Must have been detonation. Burnt the edge off two pistons.

Re: Compression gone in one cylinder
 

I am pulling it out tomarrow so we'll see.

Wouldn't you have smoke in the exhaust if the rings didn't seat? Either way it really sucks!!

I made a call and the guy told me to check the rockers - he said one probably came off. That is really giving me a bad vibe.

I did have new carbs put on the motors but I never got to wot. I only got to around 4000 or so. It still could be a lean condition but we'll see how it works out.

Re: Compression gone in one cylinder
 

Just what ex. valves were they? If not Inconel or the equivalent then my guess is that you dropped the head off #3 ex. into the cyl. Pull the valve cover and you can see just what's going on there with the valve stuff on #3. (and that dropped valve WILL cause a piston/ring/cylinder problem) --- Jer

Re: Compression gone in one cylinder
 

maybe... but the mechanical carnage would have given many more symptoms than blowby. ive got 20 bux says he detetonated a hole in the piston or broke the rings ...

Re: Compression gone in one cylinder
 

The valves look OK from the top and then the leak down showed pressure in the crank case so there is either a hole in the piston or the rings have collapsed.

With detonation, wouldn't there have been a pop or backfire or something? Wouldn't there have also been that in other cylinders and not just the one?

If there was a lean condition, what would be the cause and what would it look like when I pull off the heads? I am thinking that the installer, when he set up the new carbs, may have just got it too lean causing it to burn up a piston.

Re: Compression gone in one cylinder
 

no... in a street motor with mufflers you might hear the tell tale rattle or ping... but in an unmuffled motor even a little detonation is enough to break the rings and if it is bad enough long enough it will simply burn a hole in the piston center or eat an edge if the rings are close to the deck.

thats the nice thing about good injection... a knock sensor would have saved you probably

Re: Compression gone in one cylinder
 

Now the finger pointing begins between the builder and the installer. What do I need to look for to know what is up and who I need to be pointing the finger at myself.