new 930 rebuild
 

Have 1000 mi on 83 930. On startup after overnight, I get smoke for about 7 or 8 seconds. After that the exhaust is clean until the next day. No leaks, and followed the recommended 20 minute startup procedure and oil change. I noticed some oil residue inside the turbo ducts during tear down. Did not do any turbo work. My thought is that if it was coming from the turbo it would smoke all the time. Top end was done at rebuild. Thoughts?

Either oil seeping past turbo bearing or some residual oil dripping from heads into exchangers (unlikely as you just rebuild the heads). I would drive it until it gets much worse, then look for better turbo (K27 7200 or such). It might take few years to get there.

Sounds like one of the seals on your turbo is going.

the engine has a K27.

Does "top end" mean new piston rings? How were the cylinders?

P and C's were good. New rings went in along with rod bearings, head studs, and valve guides.

Maybe the new rings need a little more time to seat. Also, I think that you'll find people more knowledgeable than me who say that a little smoking on start up is nothing to worry about, and even happens in perfectly healthy 911/930s. My '83 SC, long since sold, did a fair bit of smoking on cold start around 80% of the time. This goes back to the early 90s. It's still doing the same thing in the hands of the friend to whom I sold it, nearly 15 years later! Throughout, the oil consumption has been in the quart per 1,500 mile range, though my friend says that he see a little increase, now. This experience proves to me that some smoking can be perfectly fine.

is turbo scavange system working okay? ..if not, oil will pressurize and can push oil past seals. Innovative Turbo can replace seals/bearings at pretty reasonable price.

the pump looked ok to me. all i did was replace the oil seal. it is a simple gear pump and i don't think much can go wrong if it turns freely and seems to function. also the tank vents to atmosphere, so it should not produce pressure. an overflow of oil into the air cleaner would not go away in a few seconds. theory busted !

was just a possibility on system not working. ...heard of that issue causing other folks problem you mention.

How many miles are on the car? Yes, the turbo sump pump is a simple device, but the gear must mesh in somewhat close tolerances for the scavenging to take place. I have heard on other threads, either here or Rennlist that the scavenge pump is not efficient at idle speeds. This would allow the sump to fill allowing the turbo seals to leak more than they normally would from back pressure from the feed side.

I tried an experiment on my turbo last Fall. Before turning off the engine, run the engine around 2000RPM for 1/2 a minute before allowing it to go to idle and then shutting off. No smoke at startup the next day! Now my K27-7006 has 80K miles on it, so its due for replacement anyway, but I thought to share that observation with you.

btw, I use Castrol syn for oil.

oh yea, one other thing. When you took the pump apart did you put the gears in so they teeth matched up as they did when you took apart? they wear into each other.

i did not take the pump apart, just changed the seal. i will try the run up idea at shut down and report results.