One cylinder low compresison
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Joined: Jan 2006
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One cylinder low compresison
All,
I am working through all the bugs of my 69 coupe and am trying to deal with a rough idle. I have traced it to significantly lower compression in cylinder number 8. I put compressed air in the cylinder and it seems that the air is seeping out through the crankcase. Adding oil to the cylinder raises compression. I think this all points to bad rings. This is a low mileage car (60k) and I suspsect that rings are stuck with carbon. The car has not been driven in 3 years.
Before I open it up, I was wondering if any of you have tried the various remedies for this. I have seen MMO, AutoRX, Seafoam, GM top engine cleaner etc. Do any of you have experience with this?
I know that many people will add 1/2 a quart of ATF and drive car. A friend also told me to dump some kerosene into cylinder and let it soak - repeating process - then change oil.
Any thoughts?
MG
I am working through all the bugs of my 69 coupe and am trying to deal with a rough idle. I have traced it to significantly lower compression in cylinder number 8. I put compressed air in the cylinder and it seems that the air is seeping out through the crankcase. Adding oil to the cylinder raises compression. I think this all points to bad rings. This is a low mileage car (60k) and I suspsect that rings are stuck with carbon. The car has not been driven in 3 years.
Before I open it up, I was wondering if any of you have tried the various remedies for this. I have seen MMO, AutoRX, Seafoam, GM top engine cleaner etc. Do any of you have experience with this?
I know that many people will add 1/2 a quart of ATF and drive car. A friend also told me to dump some kerosene into cylinder and let it soak - repeating process - then change oil.
Any thoughts?
MG
Last edited by MichaelG; Dec 14, 2009 at 11:06 AM.
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
Seafoam, MMO, or any of the other solvent-based cleaners will help. ATF will help too. How much depends upon how badly the rings are stuck. I'd try the GM Topend cleaner first, though. Solvents you pour into the cylinder may not be effective since they pool at the cylinder's low point and will not wick well enough to get everywhere. Don't do the kerosene. It has no lubricating or scuff properties and can wash out the bearings.
Racer
Joined: Dec 2007
Posts: 445
Likes: 2
From: Thomastown Mississippi
Sea Foam is good. They also make a product called Deep Creep. You can get the engine hot, remove the spark plug, spray it in the cylinder, and let it soak. Turn the engine over a few times though, before you reinstall the spark plug, to blow everything out.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
I would try the simple methods of cleaning deposits out before opening up the engine. You could have a damaged/broken/misinstalled ring in there too. But try the easy stuff, first. It could work.
