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Old 01-16-2012, 07:56 PM
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sbc 350 smoking

hey fellas. i got a stock 80s model 350. i had the truck in the shop for a transmission. and when i got it back the motor was smoking. it would smoke when i first mash the gas and when i let off the gas. the smoke is blue smoke. and it seems like its coming out both pipes. could that be the piston rings or the valve seals??

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Last edited by old west; 01-16-2012 at 08:08 PM.
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Old 01-16-2012, 08:10 PM
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More likely rings. However, why does it smoke after being in tranny shop? Did it smoke before?
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Old 01-16-2012, 08:17 PM
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nope didnt smoke before i put it in the shop. when i got it out i was driving it and the drive shaft fell out going about 80. and the guy came and got it and put in a new drive shaft and then two days later when i got it back it was smoking??? idk if he messed it up somehow or what. so i just put in another motor in it but i want to get the smoking one fixed
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Old 01-16-2012, 09:33 PM
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both more than likely...
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Old 01-17-2012, 05:40 AM
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Could be a leaking transmission modulator valve. It might be pulling tranny fluid up the vacuum line into the engine.
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Old 01-19-2012, 06:23 PM
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Quote:
Originally Posted by engineczar
Could be a leaking transmission modulator valve. It might be pulling tranny fluid up the vacuum line into the engine.
I've seen that happen a couple times before. Could be a stuck ring or two. Buy a quart of Marvel Mystery Oil and put half in the gas tank and half in the oil. Drive it around till its fully warmed up and park it overnight. Should be fine the next day.
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Old 01-19-2012, 07:57 PM
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Quote:
Originally Posted by engineczar
Could be a leaking transmission modulator valve. It might be pulling tranny fluid up the vacuum line into the engine.
This is where I would start. Basic trouble shooting dictates that when a problem shows up all of a sudden, you look for an event that has happened or what has changed or is different. Did the trans guy check for damage that the driveshaft might have caused when it came loose? Maybe not.
Terry
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Old 01-19-2012, 09:01 PM
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Quote:
Originally Posted by old west
hey fellas. i got a stock 80s model 350. i had the truck in the shop for a transmission. and when i got it back the motor was smoking. it would smoke when i first mash the gas and when i let off the gas. the smoke is blue smoke. and it seems like its coming out both pipes. could that be the piston rings or the valve seals??
Do a check on the modulator and if it's dry, do a leak down test if possible. If not a leak down test next thing is a compression test to see what the results are.

If you have dual exhaust w/no crossover connecting the two sides and you are using a divided plenum intake, unless the modulator is plumbed into the carb where the vacuum is pulled from both sides of the primary and it's not getting vacuum from an intake runner, it won't likely* be the modulator.

*There is an intake manifold heat crossover that- if open- will allow the center cylinder's exhaust to communicate. But usually the vacuum port is located on a rear cylinder intake runner.

If the valves were floated by over revving, there's a chance the spring retainer hit the valve stem seal and could have broken it, if you have positive type seals and not just the metal oil deflector umbrella/O-ring set-up. Rings are an obvious possibility.

If the exhaust pipes had to be disconnected to remove the trans there's also a chance oil or whatever got inside the pipes and could take some time to burn out of the pipes/mufflers.
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Old 01-20-2012, 07:45 PM
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I agree that the modulator is probably the problem. I had a 1976 chevy with that problem, and a new modulator fixed it right up.
Francis
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