Thread: Need Help Solving this engine puzzel

Tweet

It is not a HOT Rod question but it is an engine question I figure you guys have torn all kinds of engines. Here is the puzzel

This is a 1997 Pontiac 3.1 engine

The engine started running real rough. Note no engine codes, great plugs wires etcetc. I took a compression reading and I found that 1 of the pistons read 30psi and the other 5 read 150psi. Thinking I had burnt valves I took the head off and I found that the valves were perfect. I then poured 6 onces of tranny fluid in the sick piston and 6 ounces of tranny fluid in a good piston in the morning I found that 1/2 of the tranny fluid had leaked into the crank case and in the good piston most of the fluid was still there. So can I asssume that the rings are shot in the sick piston. Yes/NO

squirt oil in the sick pistion, and recheck compression. will verify bad rings. should read 150 wet

Originally Posted by Matt167

squirt oil in the sick pistion, and recheck compression. will verify bad rings. should read 150 wet

I did that before I took the head off and ther was very little change, It may have read 32psi vs 30psi That is why I pulled the head off thinking it was the valves

I have read it may be collapsed rings broken rings etc etc. Also the cylider walls are are perfect.

I'm thinking broken rings.........they just havn't scored the cylinder yet...........lucky you.

Originally Posted by poncho62

I'm thinking broken rings.........they just havn't scored the cylinder yet...........lucky you.

I am thinking the same, I was also told that if the rings were collapsed then soaking the piston in trany fluid "might" release them. I don't know if that makes sense I don't know what a collapesed ring is!

Originally Posted by DennyW

A collapsed ring is when the ring can no longer expand against the cylinder wall to seal it. A broken ring amounts to basically the same thing, cannot seal against the cylinder wall anymore. Tranny fluid might work. A lot of times, this is an over time thing, and the piston lands have become scored, and will capture the ring tightly. So the the metal, or carbon will not allow the rings to free up. It would be worth a try. You could soak it, tap lightly, and see if the rings would free up, but more than likely, you will have to get into it to fix it.

Thank-you for the feed-back a well informed answer. I have spent almost 1-1/2 days getting to the head gasket in this dam 1997 3.1 Grand-Am " give me a gm 350 any day" Now the next big thing is to drop the oil pan, there are over 20 items that need to be removed just to remove the oil pan. I am now at a cross roads Do I sell it for a few hundred dollars or do I spend another 2 or 3 days getting to the oil pan.

I was hoping for a miracle, I inserted a feller gauge between the piston and cylinder wall to feel the piston ring and sure enough I could feel the ring and there were no gaps between the piston ring and the cylinder wall “eliminating the collapsed ring theory” I will have to assume that a broken ring is the likely cause. The next step would be a horror story over 20 items will have to be removed just to get at the oil pan.

Originally Posted by DennyW

I re read your first few posts, and now that you checked with a feeler gauge all the way around the piston, and the ring is against the cylinder wall, I now think back to the valves, cam lobe, or similer. You said it may have changed from 30, to 32. Squirting oil in the cylinder should have brought it up more than that if it was a ring problem. Maybe you should double check your valves for sealing, and make sure the cam lobes are ok. Is there something holding a valve slightly open, and they look ok from a standard look ? Flip the head, and pour some fluid in there and see if it leaks by the valves.

I did check the valves by pouring tranny fluid and left the fluid in there for at least 8 hours and no fluid leaked out and I did tested the entire head.

The valves also move normally "non sticking" no cracks as a matter of fact the exhaust valve in the sick piston was a bright white and the a-joining exhaust valve was a light brown and the next exhaust valve was a dark black

Also please note that I did pour tranny fluid in the sick cylinder and the fluid did leak out over an 8 hour period and also note that the other good cylinder did hold all of the fluid in the same test period. Now the 2nd test I did pour paint thinner in the sick cylinder and in the good cylinder the fluid ran out of the sick cylinder in an hour or so and the good cylinder kept it the thinner for at least 6 hours

All of my fluid tests always point to bad or broken rings The other puzzling thing is that the cylinder walls look perfect on all 3 cylinders

The cam Lobes look perfect

Originally Posted by DennyW

You wouldn't by chance have any pictures you could post ?

I will do my best to post a few pics. I do have the camera Software etc etc Now I just need to learn how to use it.

If that dam oil pan was not such a big deal I would have pop that piston out just to see the shape of the rings.

One other point there is almost no ridge on any of the cyliners letting me to believe that there is very little wear. I have heard of guys driving cars over 300,000 Km with these 3.1L engines

I hate been defeated but this time I was crushed like a wine grape. It it even makes it worse when you know what the problem is and there wast not much of an option for me to fix it. It wasn't possible for me to drop the oil pan and pull the dam piston out and replace the rings. I put the engine back togethr with new gaskets and guess what same old 30 psi and a horrible mis-balance at idle. I guess I will sell it as is for a fraction of what I could have sold for with a nice running engine. Thank you all for your input.

Has any one use "Engine restore" with any success. I do know I have a piston ring broken or warn-out

Time to do a proper engine repair.

Well I used tire pressure to do the leak test and sure enough I could hear the air come from the crank case at a pretty go rate. It's amazing what one can do by improvising. I wish I had done this before I rip off the head hopping the low 30-psi was a burt valve. The leak test would have saved me 12 hours of work. I guess I learned a lot. Thanks for all your support.