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.