911 SC leak test

My 83 911 SC has done 130,000 miles and I've just had the engine leak-tested - results range from 32% to 58% which I guess isn't good.

It looks like at least a top end rebuild is needed, but should I go all the way and do a complete rebuild?

Is it OK to continue driving the car in this condition?

I'm considering undertaking the engine work myself. Any comments on this?

Many thanks.

I long have you owned the car ??? If you have had it for a while and feel you know the history or a comfortable with the overall conditiond of the engine. I would consider just doing the TOP END over. Many
of these motors have gone 200k plus miles
before bottom end work is required.

I would do the Top End over and replace the rings. If you feel comfortable with the past history of this motor....

Good Luck
Joe A

Joe

Thanks for your reply.

I've not owned the car long, so am tempted to go the whole hog while I've got the engine out.

Cheers

Phil

At 130,000 you should not need any bottom end work unless the engine has been abused.
If you have the tools and the manuals and some time you should be able to do the work your self. Bacically you do the disassembly and cleaning. Let the machinest do the machining (valve job, balancing etc.)Then you carefully re-assemble every thing following the factory manuals and Bruce Anderson's book. I know this is a short answer but the decision is basically easy, you can rebuild it if you want to and have the time.(and another car) Most, if not all parts are available and there is plenty of information from the manuals. Other owners, who have done the same things, seem always willing to help with information.
Bob W.

Thanks Bob

I've seen Bruce Anderson's book mentioned alot. Is it really worthwhile as an aid to a rebuild - I'd heard it was more of a general book about 911s?

Cheers

If you plan to keep it stock than a top end is probably the way to go. If you want to make significant performance upgrades(cams compression changes etc....) than the cautious would do the whole thing. There would be little point in risking many thousands of dollars to save a couple!

[This message has been edited by iustasail (edited 07-18-2000).]

Regarding Anderson's book;

I just got it for the purpose of familiarizing my self with the 911 engine(just put a 2.2 in my 914) and it was a bid letdown!

Its got great info on Porsche history, trivia, performance upgrades and a lot of nice pictures but is by no means a "must have" as a technical resource for the average man who is not out to build a 50K 911 engine.

I enjoyed the book and found it quite interesting; but would have liked to have purchased it as a general reference book. Instead it was all hyped up and I was expecting a detailed "how to" like the Mistro's books on 911's and 912's from the late 60's.

I think the condition of your engine is a big question mark. I would be very suspect of the 130,000 mile figure, as that sort of relatively even wear among the cylinders would be very unusual in an 130,000 mile engine. Even if the oil were NEVER changed, that would be a lot of wear (and I'm sure the oil was changed at least once in a while!).

Unfortunately, the pre-89 911's are some of the easiest cars in the world to mess with the odometer. I think there are a lot of "low mileage" cars out there that are not true mileage cars. Unless you can verify, like through service records, the original owner, etc. the mileage of an older 911, I'd be a little suspect of the mileage. I certainly would never take the odometer at face value! It should be consistent with the condition of the car, including leakdown/compression tests, seat condition, overall condition, etc.

Therefore, I'd suspect the bottom end is equally worn. There really is no reason that the top end only would be so worn. If the car is a keeper, I'd rebuild the whole engine, so you'll know whatcha got. With such a sketchy history, I think sinking $$ into top end only is false economy.

I would agree, if you have no history of this engine, you should go the complete rebuild. Personally I would split the cases anyway. I mean, if you are going to remove the pistons and cylinders, go a little more and do the complete job.
If you split the case, you can now balance the crank and rods even if the inside is ok. However you should at least replace the main and rod bearings and rebuild the rods. Also replace the chains and chain ramps. Consider replacing all the head studs to the high strength after market type.
This is a great engine and I would do the improvements that will add reliability and longitivity and not hop it up much. Consider a better exhaust. Only my opinions.
Bob W.

These posts make a lot of sense to me. Particularly the last two.

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'83 SC

Thanks very much for the input. I think I'll go for the full rebuild...

On a related matter, I've been told that the air pump increases exhuast valve wear and this should be taken off and the holes blanked. Any thoughts?

You did not mention any compression test numbers, and Bruce Anderson is not a big supporter of leakdown tests, because they ARE subject to errors, and misuse by shops trying to get into your wallet in a big way.

If you truly need a top-end rebuild, now, there would be other visible, measureable indicators, as well! I suggest a thorough evaluation, investigation and summary of the engine's current condition. Leaks of the dynamic variety can be mistaken for oil usage when there isn't an actual wear problem!

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Warren Hall
1973 911S Targa

[This message has been edited by Early_S_Man (edited 07-19-2000).]

Fair point. I'm planning to do a compression test at the weekend. Although the leak figures are high enough to suggest problems, IMO.

Your need to rebuild this engine based on a leak down test bothers me too. I have never rebuilt an engine based on a leak down and/or a compression test. I think if the engine is using too much oil and has high milage, that would be a good reason to rebuild it. You never mentioned how it ran. If it runs good, passes smog and doesn't burn too much oil, it may not need rebuilding. How is the oil pressure?
Bob W.

The oil pressure is fine according to the on-board gauge.

The exhaust is smoky when cold, but is fine once the engine has warmed up.

The car passed an MoT in February, so I assume that emmisions are OK.

Yes, it does use oil, although I've not been keeping records of quantity.

Phil,

Check the area where your crank case breather goes into the intake. If your using an excessive amount of oil, because your losing compression around the rings.. this will show up as abnormally high crank case pressure which will bring a fair amount of oil into the intake.

Also, are your valves clicking?? I just haven't heard of a SC engine needing valve guides like some of the 3.2's do. Seems a bit odd to me, as most folks say the SC can go 250K+ without a re-build.

Are you leaking oil around the bottom of the heads?? maybe you have leaky head gaskets??

When you do your compression test. Check it normally, then squirt some fogging oil (can get at a boat shop) into the spark plug hole and try it again. If the compression comes up with the oil in there, you need rings. If not, someone is jerking your chain.

Good luck

I think Porsche considers a quart every 500 miles acceptable. (Did i read that somewhere?)
Bob W.

Jeepers! isn't a quart two pints? (I'm English and we don't use this measure).

You'd be stopping on the motorway to top up!

Phil,

I have serious doubts, now, that you need a rebuild AT ALL!!!

I think you should do two compression tests, yourself, with a Sun gauge, or a similar one with a stiff, wire-reinforced flex hose, the first with the engine cold, and the second with the engine warmed up normally and driven for fifteen to twenty minutes, just prior to the second compression test ... I think the readings will be the same, and in the acceptable range! An engine that does not smoke after warming up, and passes smog 'sniff' tests is not likely to have any piston/ring/cylinder problems with Nikasil Mahle's!

I think you need to monitor your oil usage closely for at least 600 to 1000 miles, and do some close inspection for oil leaks around the oil pressure and temp senders, the oil cooler, and the oil return tubes from the cam boxes to the block!

My best guess/suspicion is that your engine is possibly a little neglected in the 'cosmetics' and leaks department, and whoever did your leakdown test observed an opportunity to take you to the cleaners, and is NOT to be trusted! Maybe it is time for you to get REALLY familiar with your car on a weekly basis, from one end to the other ... I suggest the Bruce Anderson 'Handbook' for many reasons, not the least of which is his history of the 911 engine evolution, but his 'Rebuild Fundamentals' chapter is like nothing else in print! That book is not a how-to, John Muir, style book, it is meant for a thinking audience with a working brain ... if you need hands-on guidance, take one of Bruce Anderson and Jerry Woods' classes! If you continue to depend on others to do the work on your car, and make decisions for you, I think you are going to suffer BADLY in the wallet! Porsche 911's are designed to be worked on by their owner/mechanics ... at least the ones built prior to 1990 were!



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Warren Hall
1973 911S Targa

Check your Head Studs...
Always check your Head Studs...
I am the check your Head Stud God...

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Leland Pate

___79 SC Targa