340 smoking out left exhaust only

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abodyfan

abodyfan

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I broke my 904 while on the Power Tour got it fixed. On the way to my house from where I installed the repaired transmission, I got into it a little hard and it been smoking out the left side ever since. It’s a 340 stock bottom end with x heads and a roller cam. I’m going to get back over to my shop to get it apart. This build is two years old it runs great even though it smokes. It’s definitely oil, I have changed the intake gaskets. I’m wondering what you all think? What could possibly cause this, it does have Holley Terminator fuel injection, my dad thinks it could’ve went lean and burnt a piston it is cylinder 7 causing the issue. I’m wondering if I didn’t break a ring or I had ring line up. It does have a 175 psi compression on that cylinder. When I get home Sunday I’m going to do a leak down on that cylinder my question is what does everyone think could be the issue?
 
Has nothing to do with the ring gaps lining up. That is just old urban legend. Rings turn all the time. Could be a stuck oil control ring. When is it smoking? All the time? On start up?
 
abodyfan said:
I broke my 904 while on the Power Tour got it fixed. On the way to my house from where I installed the repaired transmission, I got into it a little hard and it been smoking out the left side ever since. It’s a 340 stock bottom end with x heads and a roller cam. I’m going to get back over to my shop to get it apart. This build is two years old it runs great even though it smokes. It’s definitely oil, I have changed the intake gaskets. I’m wondering what you all think? What could possibly cause this, it does have Holley Terminator fuel injection, my dad thinks it could’ve went lean and burnt a piston it is cylinder 7 causing the issue. I’m wondering if I didn’t break a ring or I had ring line up. It does have a 175 psi compression on that cylinder. When I get home Sunday I’m going to do a leak down on that cylinder my question is what does everyone think could be the issue?
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Pull the plugs on that side...might tell you which cylinder is to blame.
 
Do a compression test and leak down test to help isolate where to look for the issue....
 
Hopefully its just a valve seal like belmateo says, and always look for the simple things first!

Jeff
 
I worked on one years ago, that smoked out of the passenger side only. Found it blew the stock steel shim head gasket towards the lifter valley, and was sucking oil from there. Inspecting spark plugs, compression test might help you diagnose.
 
It smokes the worst when idling. I know it’s cylinder 7 by looking at the plugs. When I drive and come back home it smokes a little if I let it idle after a few seconds it starts to spew smoke bad. One thing I forgot to mention is it pushing more than usual oil out of the breather on the valve cover. The breather is on the left side same as cylinder 7. It doesn’t have excessive amount of pressure in the crank case.
 
I did a compression test while doing the intake gasket it was 175psi. on that cylinder. Which it was 25psi. higher than cylinder 5 but that is due to the oil laying in that cylinder.
 
You changed the intake gaskets recently? Does it smoke it you get on it and close the throttle quickly? I have had a valve seal start to ride along with the valve. Tapped it back on the guide and hasn’t moved since.
 
abodyfan said:
It smokes the worst when idling. I know it’s cylinder 7 by looking at the plugs. When I drive and come back home it smokes a little if I let it idle after a few seconds it starts to spew smoke bad. One thing I forgot to mention is it pushing more than usual oil out of the breather on the valve cover. The breather is on the left side same as cylinder 7. It doesn’t have excessive amount of pressure in the crank case.
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Well, if it is pushing more than normal oil out of the breather, then it pretty obviously has more pressure in the crankcase. An intake seal gone would explain the the smoking, especially at idle, but not the pressure in the crankcase/under the valve cover.

The head gasket starting to fail seems to me to be the most likely explanation despite the compression numbers, and would make sense to let go when you got on it hard, and would explain both the smoking at idle and the extra oil out of the breather; IMHO, it is those 2 things together that point to the chamber seal failing, and not the intake seal. Otherwise, rings.

Have you done a leak down with 80 psi pressure in the cylinder? (Not the 15 psi that a Harbor Freight leakdown tester does....)
 
any pressure in your radiator? Head gasket is my guess with elevated crankcase pressure.
 
The radiator pressure is normal and there is no intermix. I’m going to do a leak down when I get home from vacation Sunday. I’ve been on vacation all week so I haven’t been home to check it out. I have a Matco leakage tester it has always been fairly accurate. It won’t tell me if a valve seal is bad because valves are closed.
 
It dose have Cometic head gaskets. Used them to bring the compression down a little. Thanks for all replies I really appreciate it.
 
abodyfan said:
It smokes the worst when idling. I know it’s cylinder 7 by looking at the plugs. When I drive and come back home it smokes a little if I let it idle after a few seconds it starts to spew smoke bad. One thing I forgot to mention is it pushing more than usual oil out of the breather on the valve cover. The breather is on the left side same as cylinder 7. It doesn’t have excessive amount of pressure in the crank case.
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High vacuum at idle pulls oil past valve guides.
 
Speaking of smoking.... :rolleyes:


I got talking with this chick in a bar and she asked me if I smoked after sex...
huh.gif
Toke.gif


I said, "I don't know, I've never looked..."
shock.gif


However, I have smelled burning rubber sometimes....
drive.gif
 
The increase in crank case blow by tells me you have compression getting by the rings on #7. Why will have to be determined. The high reading on that cylinder is because it is full of oil. If you have a bore scope, that might tell you something looking down that plug hole.
 
I looked in cylinder 7 with a bore scope didn’t see anything I might try to clean the cylinder out.
 
One thing you can try is air up #7 with a air compressor and listen to for where the air is escaping. Valve cover breather, Carb, or exhaust.
 
I was go to do that I can pull the valve cover off really easy I hope it’s something easy like a valve seal but I doubt it, it’s probably a ring with my luck!
 
Look down the intake ports with the bore scope....... you’re looking for one that’s oilier than the rest.

If you find one like that...... it’s likely an intake valve seal...... or the intake gasket repair didn’t take.
 
Valve seals usually suck oil during high vacuum. (when decelerating)
 
abodyfan said:
I was go to do that I can pull the valve cover off really easy I hope it’s something easy like a valve seal but I doubt it, it’s probably a ring with my luck!
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Try doing a compression test on #7 dry, then put 2 - 3 squirts of oil in the cylinder with an oil can and then repeat the compression test...

Is the reading the same with the oil (wet) and dry, or is the one with the oil higher????

If the one with the oil is noticeably higher, then you have a ring issue...

If the reading is low for both dry and wet compression test, then look in the valves or gasket...
 
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