Oil smoke re-occurance after rebuild

bigbrotherjohn · 07-10-2005, 09:26 AM

At what point should a newly rebuilt engine stop smoking, oil smoke. After my first few miles prior to initial run in the smoke completely stopped, now after about 120 miles it is back.
The smoke is not terrible but is very noticable. It came on after one of the longer runs that ive had the car on and was about a half quart low on oil, i didnt think that should be a huge deal. I am using straight weight 30W oil, non-detergent, not sure if it matters but it is pretty warm here now in the summer, 80's to 90's.
I am assuming that the smoke is from oil coming past the rings, or possible valve stem seals? Is this something that i should be worried about? Right now my plan is to change the oil and filter and keep driving normally hope for the best.

asphaltgambler · 07-10-2005, 09:42 AM

MO is that if the engine was properly rebuilt any noticable oil consumption should be gone by a few hundred miles.

bigbrotherjohn · 07-10-2005, 09:48 AM

yeah thats what i thought, and it is only at 120miles, but the thing that concerns me is that the oil smoke went away and then returned a few days later.

Early_S_Man · 07-10-2005, 10:19 AM

My feeling is that you should only have used the non-detergent oil during the first 20 or 30 minutes to seat the rings ... not during any driving at all! That oil does not meet any factory specs for engine protection!!!

Change the oil to a high-quality 20W-50 oil, IMMEDIATELY, and hope for the best!

asphaltgambler · 07-10-2005, 10:36 AM

Yes, I agree here as well. Don't panic yet! Change the oil and filter and see what develops then. Good Luck!

bigbrotherjohn · 07-10-2005, 11:52 AM

Just to clarify about the oil used, the car is a 912 and it was recommended to me to use straight weight 30w nondetergent for first 300 miles, i might switch to what early s man said because it will probably be a higher quality, i just really dont want to wreck something that i spent all the time and money putting together.

quote from Duane Spencers The Complete Porsche 912 Guide
"I have had good luck with 30W non-detergent oil in these engines dunring the first few hundred miles of break-in." pg. 77

bigbrotherjohn · 07-10-2005, 02:03 PM

Just did a compression test, 112.5,110,105,112.5. Pretty good i think, i did find one spark plug with oil on it though, not the low cylinder however. Hopefully everything will be fine with soem more time and new oil, any more suggestions or reinforcments would be appreciated, thanks.

Early_S_Man · 07-10-2005, 02:45 PM

What cylinders and pistons are in the engine now? Wasn't the stock compression ratio 9.3:1? If so, those numbers are at least 60 psi below what I would expect after a rebuild ...

Let us know if you find fine metallic iron deposits in the oil when you change it ... could be signs of premature camshaft wear.

Formerly Steve Wilkinson · 07-10-2005, 02:46 PM

Don't worry about using nondetergent oil. We use it to break in flat-four air-cooled aircraft engines that see a LOT harder duty than any 912 ever will, and nobody worries about changing it out after 20 or 30 minutes. More like 20 or 30 hours.

Stephan

911 heathen · 07-10-2005, 04:02 PM

A similar question was posted at JZMachtech in the UK......this is their reply..

It is very hard to say with out seeing the car and checking a few things why this is staring to happen. It may be as simple as the grade of oil which has been used. We always run the engine on a cheap oil (Castrol GTX Plus) for the first 1000 miles, after this we carry out a first service and then use Castrol Magnatec (10w/40). The reason for using GTX Plus for the first 1000 miles is to allow the piston ring to bed in with the barrels. This is very important and it can only happen with this type of oil as most modern oils give too much protection and can polish the bores which can cause problems.
If you can find out what oils have been used on your car please let me know.

You should not use semi synthetic oil for running in and you should have had a service by now. I would ask them to renew the oil using normal mineral (15w40 or 10w/40) oil and then run the car for a few thousand miles and then get the tappets check before switching back to synthetic oil.

bigbrotherjohn · 07-10-2005, 05:09 PM

Early S Man, the cylinders are the typical 86mm japanese ones and the compression ratio is around 9:1. The engine was not warmed up before the test and the gauge is old, i was not very worried about what the numbers would be but happy to see that they were pretty similar.

I adjusted the valves right before the compression test and the oil that i saw looked a bit dark. It wasnt grainy or burnt but it wasnt as clear as last time I changed the oil. I will drain the oil in a few minutes and check out the magnetic plug for any metal.

bigbrotherjohn · 07-10-2005, 06:34 PM

Ok, for anyone following this, I'm pretty sure I've found the problem, or at least the beggining of the problem. Drained the oil and found some scary metal peices. I'm not certain what it is but think its probably a wrist pin clip. So the new theory is that a wrist pin clip found its way out and broke the oil ring on one of the pistons, allowing oil into the combustion chamber. Ill tear down the engine this week though and keep you guys posted.

any one else think it could be a clip, I cant really think of much else

bigbrotherjohn · 07-11-2005, 06:36 PM

For any one following this, tear down pics are here

Engine failure , circlip ?