Hi Everyone,
Need a little help here. I have an 89 convertible. It has the V12, 111K on the odometer. Previous owner started disassembling the engine, told me it was only firing on 6 cylinders, so he decided to swap it. I also got an extra V12 engine with the car. The engine in the car has Marelli ignition, so I figured I had a Marelli situation. Decided to run a compression test on it. Bad news. 2 cylinders (bank B #5 & #6) 0 compression. Zero. Rest were all around 160 or better.

Decided to run a compression test on extra engine. Removed plugs, squirted a little light oil in each cylinder (had not run in a looooong time) rigged up the starter and cranked her. Compression was better in this engine. Many cylinders around 200. BUT, Bank A # 3, 5, and 6 were less than 100. My question is, could those low readings be attributed to this engine sitting for years? I am puzzled as to why you would get 200+ PSI on 9 cyl and 70-90 on 3 others.
Any insight is greatly appreciated!!

 

How long has it been sitting? Some possibilities include valves sticking, valve face/seat face corrosion and the rings sticking to the piston and not sealing properly.

 

Sounds logical. I did think of a sticking valve or two. Would you agree this engine is probably OK? I have no way of knowing how long it sat, but it was "stuck" at first, would only move an inch or two. That's why I oiled the cylinders. I was told it had 25,000 miles on it. The compression on the "good" cylinders would indicate little wear to me. Hopefully it's a valve or minor ring issue. Thanks for the insight!!

 

It's not uncommon for an engine to get "stuck" after sitting. The piston rings tend to get rust that binds them to the cylinder walls. Usually no big deal - just do what you did and hope they break loose without breaking anything. :-) My boat was like that when I saved it from sitting for years. Runs like a champ now.

You might want to pull the head on this engine before you put it in the car. Much easier to do out of the car and that'll give you a chance to eyeball the valves. Should replace the seals an gaskets anyway. Could save yourself some headaches.

 

take the spark plugs out and dump a little diesel fuel in each cyl let it soak for a day spin it over a few times by hand then repeat for a few days then test compression again.

 

Thanks to everyone who responded. I followed your advice, as well as removed the intake and valve covers and lubed everything as well as I could. Compression on the 3 low cylinders came up drastically, almost as good as the others. I think this engine will work fine. Going to get it up on an engine stand and go over it. Ran the numbers, it is a 1982 HE. Should work fine for my car (89).
Again, thanks for all your suggestions!