BLUE SMOKE......panic ensues!!

[Sunroof]

I own a 1973.5T 911 with the 2.4 engine coupled with the 915 tranny and fueled by CIS. I have owned it now going on 19 years. The engine had a total rebuild at 92,000 miles back in 1991. Today my odometer is reading 174,000 miles and the engine still pulls strong with no unusual noises while driving.

On start up ordinarily I will get some smoke (blue) that's lasts only a minute before it clears. I attribute that to the oil that accumulates when sitting awhile and expected from an older air cooled engine, BUT recently, I have noticed that the smoke coming from the exhaust (blue) is prolonged and when I drove it last (yesterday), at the stop lights I could see smoke out my rear view mirror. Panic of course ensues!!!!

It would be wonderful if all it took was a valve adjustment (the valves are extremely noisy) or if its a simple mixture adjustment, but my gut tells me its the old valve guides or bad rings. Could it be something simple since it feels engine performance is still excellent? So, with this information, I am asking the knowledgeable reader, how does one test for or determine the cause for such a problem? Or do they not know until they tear it down?

The second part of course is what can I expect to pay for a valve job on a 2.4L air cooled engine these days? Or do I just add a can of Bardol or Marvel Mystery Oil and call it done?!

Any feedback is well appreciated. I am going to continue to post to next find out what shops in Atlanta have the best reputations for doing such work on the older engines.

Bob
1973.5T

[bkreigsr]

Have you looked at the plugs?

Bill K

[Coastr]

Step 1 : Italian tune up
Step 2 : Conpression / leak down test
Step 3 : Post results for discussion

[Sunroof]

What's an Italian Tune Up?

[Sunroof]

What could an oil-fouled plug tell you? How can you determine rings from valve guides?

[bkreigsr]

Originally Posted by Sunroof

What's an Italian Tune Up?

google

easier to look up than to explain

[bkreigsr]

Originally Posted by Sunroof

What could an oil-fouled plug tell you? How can you determine rings from valve guides?

...so your plugs are oil fouled?

If it was the rings, compression would be outside spec.

At 174,000 on a '73.5, best not to take any shortcuts and bite the bullet for a full tear-down and rebuild.


Bill K

[manbridge 74]

Has it sat for some time? We tore down a stuck in a body shop, sat forever, blue smoke 75 and found the oil control rings were packed tight with carbon, no moving them without extreme effort.

Maybe you could use some sort of BG engine oil cleaner to see if it makes a difference but I’d put success rate of chemicals at less than 10%.

Maybe the valve guides weren’t replaced before. There had been some new guides made too large; perhaps these went in at last rebuild.

Leakdown/compression tests would be next step for me.

[Sunroof]

No have yet to check the plugs....

Yep, I did an "Italian Tune Up" yesterday and ran the hell out of it only to see occasional smoke when at a stop light. Is their anything in the valves being very noisy that could be the issue?

[Sunroof]

Jeff. Engine had a full rebuild with new valve guides back at 90K or so. The car gets driven during the weekends so does not sit for more then a week or two without a run. I want to keep bring up very noisy valves, since adjustment has been awhile. Can loose tappets be a concern.

Bob

[manbridge 74]

Valve adjustments are every 15K on these so yes check them. Loose valves won’t cause smoke but if the noise is still present after adjustment it can be loose/worn guides.

Post a vid with engine running at its noisiest.

[tobluforu]

Could you have over filled it?

[QueWhy]

Originally Posted by bkreigsr

...so your plugs are oil fouled?

If it was the rings, compression would be outside spec.

At 174,000 on a '73.5, best not to take any shortcuts and bite the bullet for a full tear-down and rebuild.


Bill K

He has 91,000mi since last rebuild. 174,000 total miles.

[Sunroof]

I know that overfilling with oil can cause smoke since it accumulates (puddles) in the air box. I try to keep the oil level at the halfway mark on the dipstick, so I do not think that's the issue. When the engine was rebuilt back in 1991 the bronze valve guides were used. I would think worn valve guides would be slow in showing wear, not all of a sudden!

[pmax]

For the 2.4 and below, 60-70K between top end is normal ( Bruce Anderson's handbook ).

You can also pull the HEs and have a lookie look at the valves.

[da Vinci Dan]

It’s easy to jump to a worse case scenario especially given the miles. But, you’ve taken good care of her and did a quality rebuild. Have confidence in that.

Take your time and patiently and logically work through what you know needs to be done. Start simple with good diagnostics. You know you need to adjust the valves and look into the ignition. Check the plugs... You’re getting way ahead of yourself thinking about rebuilt cost.

Slow is smooth and smooth is fast.

[Sunroof]

The rebuild was done by the previous owner who spared no expense. One of the reasons I bought it was that a Georgia Tech graduate named Ghalen Bridges rebuilt the engine, which would be analogous to having a home built by Frank Lloyd Wright! Ghalen in his hayday built just so many engines and folks have said, "if you do not get 250K out of her something is wrong"! Ghalen was a perfectionist. The engine has always felt very tight and still does, but this just happened. I will take a look at the plugs to see what they look like and go from there.

The knowledge and experience on this board is second to none in the Porsche community and I value everyone's opinion.

thanks
Bob
senior member

1959 Austin "bug eyed" Sprite
1967 Triumph TR-4A IRS
1972 Fiat 850
1974 Porsche 911
1979 Porsche 911SC
1985.5 Porsche 944

[RedCoupe]

Sunroof, I would perform a dry/wet compression test. That will help tell you if the issue involves the rings or just valve guides and or valve guide seals. Briefly, it involves performing a normal compression test and recording the results. Then, add a bit of engine oil to each cylinder to seal possible leakage past the rings and rerun the compression test. If the compression numbers noticeably improve after adding some oil to the cylinders, you know that have leakage past the rings. If there is very little change, then you can assume that the oil leakage is past the valve stems because of worn guides or seals.

[pmax]

How often do you check the oil level ?

[Coastr]

If you got less smoke after a good flogging, now check after the car has cooled completely. Is it better?

The ‘science’ behind an Italian tune up is to get the engine hot, put a lot of airflow/fuel through it. Any carbon pieces, sticky rings or others can get shaken loose.

It doesn’t fix worn rings or valve guides. That’s what the compression test and leakdown is for.