Rebuilt question /long
Thread Starter
Junior Member
Joined: Jul 1999
Posts: 37
Likes: 0
From: Ottawa, Canada
Car: 1985 Camaro Z-28
Engine: LG4
Transmission: 700R4
Rebuilt question /long
Lately my car smokes more than it use to. Once in a while it smokes a little at startup
but now when I hit the gas pedal at WOT it smokes alot. I assume I have leaky valve seals. Anyway I was thinking of rebuilting the top end of the engine, now is that a good idea or not (assuming the bottom end is in good shape) because I have been told that rebuilting only the top end wont last? I'm not a mechanic but I'm not dumb either so assuming I do a compression check and everything seems fine could I consider that the bottom end is in great shape? I would pull the heads off send them to a shop to rebuilt them (maybe buy some better heads if I have the money) change the peanut cam, the intake and rebuilt the Q-jet. By the way the motor is the LG4 (and I want to keep it so dont tell me to go get a 350). So guys what do you think.
Thanks!
but now when I hit the gas pedal at WOT it smokes alot. I assume I have leaky valve seals. Anyway I was thinking of rebuilting the top end of the engine, now is that a good idea or not (assuming the bottom end is in good shape) because I have been told that rebuilting only the top end wont last? I'm not a mechanic but I'm not dumb either so assuming I do a compression check and everything seems fine could I consider that the bottom end is in great shape? I would pull the heads off send them to a shop to rebuilt them (maybe buy some better heads if I have the money) change the peanut cam, the intake and rebuilt the Q-jet. By the way the motor is the LG4 (and I want to keep it so dont tell me to go get a 350). So guys what do you think.
Thanks!
Junior Member
Joined: May 2000
Posts: 91
Likes: 0
From: AK
I’m assuming the engine is in stock configuration. If not, then there are more possibilities of smoke that I have not listed below.
Smoke after start is usually valve seals. Stock seals are cheesy little o-rings placed on the valve stem. They reduce the amount of oil that has “splashed” onto the stem from running down the stem into the intake ports. Another seal is an “umbrella” seas that does the same thing but works a bit better. Positive seals are pressed onto the top of the valve guide and provide a positive valve stem seal as it strokes up and down. They work much better than the other two. They are on most aftermarket heads and require machine work to the top of the valve guide on stock heads (most stock heads). When the seals fail, oil will run down the stem into the intake ports and oil will puddle on top of the piston or accumulate on the top of the valve when the engine is off. When the engine is first fired, the accumulated oil burns.
If the engine is smoking at WOT, this is an indication that the valve stem to guide clearances are excessive. Vacuum from the intake port will “suck” oil through this excessive clearance. The other culprit for WOT smoke is ring seal failure. The oil ring and second ring stop effectively scraping oil from the cylinder walls and it will be burnt during the combustion process. When at WOT or high rpm, crankcase pressure will be higher because the combustion gasses are not effectively sealed above the rings. One quick way to check for ring failure is to hold a piece of toilet paper above the dipstick tube (with the dipstick out). Rev the engine and observe the paper. If it indicates gasses blowing out the tube, then ring failure is most likely the culprit. If the paper is drawn into the tube, then the guides are most likely the culprit.
A compression test will only indicate that one or more cylinders are having problems. A leak-down test is the better method to determine ring/guide failure. This procedure pressurizes the cylinders (piston at TDC compression stroke) and you can observe how fast the pressure drops. 10#’s in 60 seconds is sign of problems. If it drops, squirt a few drops of oil into the cylinder and rotate the engine a few times. This will help seal the rings if they're leaking by. If pressure drop does not diminish, then the rings are most likely bad. If you do not notice a significant pressure drop, then the guides are most likely bag.
I hope this helps you out.
Mike
****Edit, I should really proof read before I hit Submit. Had to fix that last paragraph. ****
[This message has been edited by md (edited November 03, 2000).]
Smoke after start is usually valve seals. Stock seals are cheesy little o-rings placed on the valve stem. They reduce the amount of oil that has “splashed” onto the stem from running down the stem into the intake ports. Another seal is an “umbrella” seas that does the same thing but works a bit better. Positive seals are pressed onto the top of the valve guide and provide a positive valve stem seal as it strokes up and down. They work much better than the other two. They are on most aftermarket heads and require machine work to the top of the valve guide on stock heads (most stock heads). When the seals fail, oil will run down the stem into the intake ports and oil will puddle on top of the piston or accumulate on the top of the valve when the engine is off. When the engine is first fired, the accumulated oil burns.
If the engine is smoking at WOT, this is an indication that the valve stem to guide clearances are excessive. Vacuum from the intake port will “suck” oil through this excessive clearance. The other culprit for WOT smoke is ring seal failure. The oil ring and second ring stop effectively scraping oil from the cylinder walls and it will be burnt during the combustion process. When at WOT or high rpm, crankcase pressure will be higher because the combustion gasses are not effectively sealed above the rings. One quick way to check for ring failure is to hold a piece of toilet paper above the dipstick tube (with the dipstick out). Rev the engine and observe the paper. If it indicates gasses blowing out the tube, then ring failure is most likely the culprit. If the paper is drawn into the tube, then the guides are most likely the culprit.
A compression test will only indicate that one or more cylinders are having problems. A leak-down test is the better method to determine ring/guide failure. This procedure pressurizes the cylinders (piston at TDC compression stroke) and you can observe how fast the pressure drops. 10#’s in 60 seconds is sign of problems. If it drops, squirt a few drops of oil into the cylinder and rotate the engine a few times. This will help seal the rings if they're leaking by. If pressure drop does not diminish, then the rings are most likely bad. If you do not notice a significant pressure drop, then the guides are most likely bag.
I hope this helps you out.
Mike
****Edit, I should really proof read before I hit Submit. Had to fix that last paragraph. ****
[This message has been edited by md (edited November 03, 2000).]
Supreme Member
Joined: Mar 2000
Posts: 13,414
Likes: 6
From: Central NJ, USA
Car: 1986 Firebird
Engine: 2.8 V6
Transmission: 700R4
Are all valve seals on the 3rd gen "stock" heads, whatever came with the engines, o-rings?
I finally got that "rebuild your GM 60 degree V6 (2.8/3.1/3.4)" book, and it showed umbrella seals on the "Generation II" v6 heads. Those were specially designed heads, though.
Just wondering if all the v8 heads used o-rings stock. Thanks!
------------------
-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!
I finally got that "rebuild your GM 60 degree V6 (2.8/3.1/3.4)" book, and it showed umbrella seals on the "Generation II" v6 heads. Those were specially designed heads, though.
Just wondering if all the v8 heads used o-rings stock. Thanks!
------------------
-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!
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