340 smoking bad

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1968dartman

1968dartman

life is getting better!!
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My 340 has learnt a new trick that I am NOT liking. It smokes while running and REALLY smokes when I get after it. I am going to do a compression test and leakdown test. Any thoughts as to what it might be. Both banks are smoking, but one worse than the other. I thought it might be valve seals as the motor sat for seven years before I got it. The oil pressure is real good if that helps. The motor seems to run really well, starts well and seems to still be making good power.
 
Is this something it just started or has it done it ever since you got it running from sitting up?
 
Could it be head gaskets? Checked your oil and fluid levels for leaks? If the valve seals were old, might be time to pull the heads and replace them, slap in some new head gaskets and lap the valves if needed.
 
Oil has always been nice and clean with no off colour. One head gasket is recent as I had one head off when I got the car two years ago. I am not sure if the valve seals will cause the motor to smoke the way it is, which concerns me! I have not done anything to the motor this year other than removing the intake to clean it.
 
It really sounds like the intake gaskets aren't sealing. You could be sucking oil from the lifter valley.
 
If the idle is not rougher than it used to be, I'd guess valve seals like you said. Test for vacuum leaks on the outside of the intake manifold and carb with propane - does the idle get smoother? If so, then you have a vacuum leak for sure. It could be leaking on the inside too (like in the lifter valley area). Im not sure if there is a good test for that. I might try placing some propane down the oil filler, but then it could also go in thru the valve seals too.
 
Did you read your plugs yet to see if it's just one plug, one bank, or all cylinders?

I would suspect that if your intake is pulling oil, you'd have other issues.
 
I would start by pulling plugs, my car was puffing smoke earlier in the year. Ended up being a fuel issue. A quick rebuild of the carb and a good tune took care of everything ! Good luck ...
 
Ok i don't want to step on toes since i'm new here but when you say it smokes is the smoke a blueish color and stays in the air a long time or is it whitish in color and disappears quickly. If it is bluish and lasts a long time like you are killing every living thing in the area that is oil but if it goes away quickly then it is water vapor. Depending on the color you can figure out what is burning. How much oil are you using ? If it is oil the first thing to do is figure out how it gets in the combustion chamber. The pcv valve, the under side of the intake manifold, the rings ? If the smoke started all of a sudden something is broken but if it has been getting worse over time then something is blocked and the oil is being push in the combustion chamber to be burned. Depending on the age of the engine it could be intake valve seal but the smoke should go away after 5-8 mins of runing but you wil still be using oil that is why you need to know how much oil you are adding. If it is oil it will flow the spark plug in a short time of driving and you will have a dead miss. If the smoke is whitish then you may be burning coolant from a leaking head gasket or a cracked head. It is very important that you figure out what is going on before you disassemble the engine in any because if you go the disassemble route you may never figure out what the problem is. Pm me if you need more help ok
 
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