Smoking at start-up cured! (I think)

[BRAINIAC]

I may have stumbled onto a cure for some excessive smoking on start-up. After I rebuilt my engine 5 years ago, I noticed that my peak oil pressure was alarmingly high. To reduce it I put thicker washers between the safety bypass bolt and the crankcase. I was worried about blowing out my looil filter on cold mornings. I think I had fixed a problem that really wasn't there. My gauge was reading falsely high. Fixed that but never put the washers back to normal. Just forgot about it. Until recently while doing an oil change, I remembered. Since I put it back to normal I haven't had any smoke! I believe the lower spring pressure may have been allowing the bypasss to open too soon and too much, dumping the extra oil back into the crankcase and flooding the bottoms of the pistons, causing the smoking. Just a theory. Can't explain it but it I can't ignore the fact that my car doesn't block out the sun on start-up anymore. Maybe some of the cars that have this problem have bypass valve issues. It's an easy theory to test and a cheap fix too if it works.

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Tyson Schmidt
72 911 Cabriolet
92 C-2 Cabriolet

[movin]

I'm interested in this, mine sometimes smokes at start-up also. Where is this safety bypass bolt? How does it affect oil flow?

[RoninLB]

Brainiac........Have been waiting for an educated thread. Either your theory doesn't hold oil or someone is still trying to figure out a reply. Maybe it's a party weekend and I just have to wait it out...............Ron

[BRAINIAC]

I'm kind of uncertain myself if they are just coincidence. But the 78 and 79 SCs had a bypass valve problem that would cause excessive smoking and power loss when hot. The crankcase was getting flooded because the relief valves were dumping all the oil back into the crankcase and the scavenge pump couldn't keep up. I just sort of put 2 and 2 together and figured that must be what was happening with mine.

To clarify, I'm talking about *excessive* smoke at start-up. Not the typical little puff. Some mornings my car would block out the sun for 2 minutes of running when it was cold out!

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Tyson Schmidt
72 911 Cabriolet
92 C-2 Cabriolet

[RoninLB]

BRAINIAC........When I rebuilt my 77 2.7 there was up-grades. Oil psi. relief and safety valves up-grade became an issue during 1978 model year, oil pres. and oil level would suddenly drop during high-speed driving...........That is all I know about those valves...........Ron

[Early_S_Man]

Tyson,

Did you do the oil passage mod, plugging the bypass port and milling new hole in supply pump inlet at the time of your rebuild?

The '78-'80 'issues' involving SC oiling had nothing to do with relief valves ... it was an oil pickup issue!

The pressure relif valves' style were changed in '76 when the size of the scavenge pump was reduced for the Turbo engine.

The length of the relief valve springs in an engine 10 years old or more have always been a concern of mine, after having found many weakened, shorter springs in VW engines. It would behoove 911 owners to check the lengths, and replace any shorter springs that are 69 mm or less, since the new spec is 70.0 mm, and longer springs 85 mm or less that are supposed to be 86.0 mm.
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Warren Hall
1973 911S Targa

[This message has been edited by Early_S_Man (edited 07-01-2001).]

[movin]

Early_S_Man,
I'm interested in this subject too. Where are these springs accessed from? What is the proper length for the various years?

[Early_S_Man]

Movin,

I don't remember the exact date of the change, probably '80-'83, when the longer 86 mm spring and guide were installed in production.

The plugs have large screwdriver slots and a specific tool is not readily available, but large 1/2" drive bits called 'drag-link bit' can be filed or ground to the approximate 1/8" x 3/4" dimension needed, and it MUST BE A PRECISE FIT! The plugs and valves are oriented vertically in the right-hand crankcase half, and horizontally in the left-hand case half. Both valves are clearly shown in the following oil system diagram from the 1974 brochure:



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Warren Hall
1973 911S Targa

[This message has been edited by Early_S_Man (edited 07-01-2001).]

[lsolon]

Hey Brainiac, Is this a fix you tried on your 72. I have a 72 that does the same thing. Sometimes it will smoke like hell at start up. Sometimes not at all. It has about 40,000 miles on a rebuild. Not really sure what people are getting at with the replys since I don't know a damn thing about this subject. My question to all is, " could this work?" and how do i do it?
Thanks

[BRAINIAC]

Warren, no, I didn't do the update. It's all stock 72 oiling system.

Isolon, yes it was on my 72. Sounds like you should do what Warren stated above about the springs. It's easy enough and cheap enough. Worth a try. The pressure relief valve is the hard one to get at. (it's the horizontal one in the side, need to remove the heat exchangers for best access)

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Tyson Schmidt
72 911 Cabriolet
92 C-2 Cabriolet

[lsolon]

Thanks all.