Blue Smoke

[mygatts57]

I'm at 150 miles on break-in of my rebuilt 2.2T 911. Recently it has started blowing a fair amount of blue smoke, particularly when de-accelerating down a hill in 2nd with the clutch out to put back pressure on the pistons. Another piece of information is that the carbs aren't running as smoothly as they should which I hope to rectify @ 1000 mile time.

Is the blue smoke normal for early break-in? and could the better than stellar catb performance contribute to the problem? Thanks.

Dave

[mygatts57]

whoops. "better than stellar catb performance" should be "less than stellar carb performance"

[VitoV]

Blue smoke = oil. Black smoke = fuel.

A carburetor problem will not produce blue smoke.

Blue smoke on the overrun is typical of a car needing a top-end rebuild. Oil is drawn past worn or inadequately sealed intake valve guides into the combustion chamber.

If your engine in producing oil smoke at other times as well, there may be other stuff going on, but again, blue smoke will not be related to a carburetor issue.

[mygatts57]

The overhaul included professionally rebuilt cylinder heads. Any chance it could be valve adjustment?

[bullethole]

did you check valve clearance when you re-assembled the motor. Valve adjustment should not affect the seals, but if your clearance was not right, you might have bent a valve in your shiny new motor , which could be the source of the problem. If you had a shop do the motor for you i'd take it back to them and get them to resolve the issue.

[mygatts57]

It's a T engine and I checked all piston/valve clearances during assembly including rolling a couple of pistons on each side through a couple of cycles with the adjustment screw dialed down the specified anount, with no interference.

I'm at mile 150 since overhaul. Some posts suggest that it just may take a few more miles for the rings to seal. The smoke only seems to appear on overrun and this early model doesn't seem to have anything that compensates for overrun? - The engine has webers. Your thoughts?

Thanks

[Flat6pac]

Probably the oil in the heat boxes from before the rebuild. Run the engine at 3k for a while and then go to 4 k and run a while. You have burned all the oil that will smoke at those rpms so in the future if you blast to 5k and see oil, its the oil that didnt burn off at 4k....if that makes sense.
Bruce

[mygatts57]

Thanks Bruce. I can still hope that it is all it is. This does square with the fact that it appears as the engine gets hotter. I suppose the overrun phenomenon is that that it pushing a greater exhaust volume through the exchangers? Thanks again