Piston rings or valve seals?
Thread Starter
TECH Apprentice
Joined: Sep 2012
Posts: 327
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Piston rings or valve seals? So i bought a used LS1 motor from the junk yard and unfortunately, i think i will have to return it back.
Motor smokes ALOT when i accelerate hard. It does that only at high rpms. However, i think this is not from the engine but rather from the oil filled exhaust system.
My previous engine had a couple of really bad piston rings. Oil used to literally drip from the exhaust and i used to put a quart everyday. Drove it like that for about 3 months. So now i figure when i rev the engine hard, the heat is burning the oil in the muffler/exhaust system, hence the blue smoke. To be sure, i disconnected the exhaust pipe at the headers and reved the engine a few times...no smoke at all.
However, after the above test, i did a compression test. When i pulled out the spark plugs, only one of them was oil fouled, the rest were only a little "ashy". Compression test for that cylinder was 185-200. Whereas the rest were between 174-176.
What does this mean?
Motor smokes ALOT when i accelerate hard. It does that only at high rpms. However, i think this is not from the engine but rather from the oil filled exhaust system.
My previous engine had a couple of really bad piston rings. Oil used to literally drip from the exhaust and i used to put a quart everyday. Drove it like that for about 3 months. So now i figure when i rev the engine hard, the heat is burning the oil in the muffler/exhaust system, hence the blue smoke. To be sure, i disconnected the exhaust pipe at the headers and reved the engine a few times...no smoke at all.
However, after the above test, i did a compression test. When i pulled out the spark plugs, only one of them was oil fouled, the rest were only a little "ashy". Compression test for that cylinder was 185-200. Whereas the rest were between 174-176.
What does this mean?
Last edited by Freefallin; Jan 8, 2014 at 03:24 AM.
Since your one cylinder that had the fouled plug is showing HIGHER compression than the rest I'd be willing to bet you have a bad valve stem seal on that cylinder. You are leaking oil into that chamber and are essentially doing a "wet" compression test giving teh higher numbers. I would not return an entire motor for that. 241 heads are stupid cheap. And it may just be the seal under the valve spring. I'd do a little more investigation and then talk to the junkyard. See if they'll cover gaskets if it is the seal.
Thread Starter
TECH Apprentice
Joined: Sep 2012
Posts: 327
Likes: 1
Since your one cylinder that had the fouled plug is showing HIGHER compression than the rest I'd be willing to bet you have a bad valve stem seal on that cylinder. You are leaking oil into that chamber and are essentially doing a "wet" compression test giving teh higher numbers. I would not return an entire motor for that. 241 heads are stupid cheap. And it may just be the seal under the valve spring. I'd do a little more investigation and then talk to the junkyard. See if they'll cover gaskets if it is the seal.
Go with simple first, don't jump into the major stuff until you have eliminated the simple.
The valve seal is simple to replace. short version remove the rockers, use an air fitting to put air into the cylinder, compress the valve spring and remove the locks, remove the spring, remove the bad seal, then reverse the process.
The type of vehicle will effect how long it takes F-bodys are a little more difficult due to the engine set back.
If you are going to do one you might as well do them all.
I'm sure you could fine a detailed how to somewhere.
Good luck.
The valve seal is simple to replace. short version remove the rockers, use an air fitting to put air into the cylinder, compress the valve spring and remove the locks, remove the spring, remove the bad seal, then reverse the process.
The type of vehicle will effect how long it takes F-bodys are a little more difficult due to the engine set back.
If you are going to do one you might as well do them all.
I'm sure you could fine a detailed how to somewhere.
Good luck.
