windsurfar

Looking at an 84 911, that has a short bell housing G50 conversion with an Andial 3.7 cylinder and piston set installed and it has been twin plugged. Bored case to 102mm inner and 107mm outer for the build. Only 20,000 miles or so on the engine and G50 conversion.... but my PPI says there is oil leaking from where the cylinders meet the case, leak down is 30-40% on all cylinders, and compression is 130 Psi on the cylinders. I think these numbers are pretty worrisome, I am guessing needs a top end soon, and diagnose where the leaks are coming from. Lots of receipts for work from a very reputable shop in LA. Car runs very strong, cold start no smoke, and no smoke when warm. Thanks to all who respond. Also only a few drops of oil on ground per week, and no oil added over the last 1000 miles, so oil leak is minimal.

Catorce

What kind of assurances are you looking for here? Either way, sounds like if you want to be leak free, you're going to want to reseal the motor at the very least.

Also, cold start smoke is very very common on 911s because of the engine architecture, the fact you don't have it (yet) is plain luck.

windsurfar

No visible smoke on cold start, I guess lucky. Think i will do a top end rebuild. Getting a dyno run in next couple days, will post.

Steve Weiner-Rennsport Systems

I would be measuring the cylinder bores for concentricity since these tend to go out of round. If this is the case, you'll never get decent ring sealing.

windsurfar

Dyno result topped at 280 wheel HP, 250 TQ. Run ended due to oil return tube spraying oil on muffler and causing smoke. Obviously the car needs some work, but this is a strong HP number, confirms what the guy doing the PPI said about the engine being "VERY strong".... but I am now doubting the technique of the leak down tester, 30-40% leak and only 130PSI compression per cylinder doesn't seem to jive with these strong HP numbers on DYNO run. Comments?

windsurfar

Hi Steve, thanks for the reply, I guess this means sending it to a machine shop, if no longer concentric, to make right?

Steve Weiner-Rennsport Systems

My pleasure!

Engines with less than ideal leakdown values can still make decent power on the dyno, I've seen this quite a few times.

Depending on how far the cylinders are out of round, sometimes they can be bored and re-plated (nikasil) back to the original bore size. The bigger issue is that many thin-wall cylinders simply lack sufficient mass to stay round once they have heated & cooled several times and the problem remains chronic. For this reason, we are VERY careful about maintaining sufficient wall thickness to prevent such issues.

windsurfar

Thats interesting Steve, thanks again.
I guess the only way to resolve this is to have another person do a leak down test.
Do you know of this unusual and rare cylinder and piston set Andial made for the 3.2?
I would be surprised if the cylinder walls were made "thin"... based on your comments that would seem to invite problems in the future. My understanding is the case is bored, but the cylinders would be made to be strong and durable.
This 911 with 20,000 miles on the rebuild, is making 330 crank HP just under 6,000 RPM (before stopping prematurely because of smoke coming out of the passenger side of the back of car ...no smoke out the tail pipes). Thats a pretty impressive HP. I am guessing the compression ratio must be high, maybe 11.5:1, and the chip tuned to perfection for the aggressive cam and twin plug configuration.

Steve Weiner-Rennsport Systems

I'm familiar with that special Mahle P/C set, yes. Its 10.3:1 CR.

Mahle made several custom P/C sets for these express purposes and some of them were considered 'thin-wall'. These units were well known at the time to not be as stable as the other thicker wall versions which tended to stay round.

Charles Navarro

The Andial kit made for some great torque with all that added displacement. We used to make a 102/107 Nickies cylinder as a direct replacement for the Andial set, but I stopped stocking it several years ago in favor of a 102/106.5 to give a bit more sealing surface at the case register and we even have since pushed it to a 102.7.

windsurfar

Thanks for your reply Charles.

windsurfar

SO i need to make a decision on this car. The HP and torque are great, overall condition is good to very good, no rust, great interior, paint, brakes, suspension, transmission and clutch, tires and wheels all good... with oil leaks noted on PPI "engine oil leaking from valve covers, pushrod tubes, and where cylinders meet case" although they stated the case was in good condition. Current dealer claims only a few drops of oil per week, and no oil added over the 1000 miles he has driven the car.

Here is a screen shot showing the location of smoke pouring out from under the car, smoke started i am guessing around 4000 RPM and really started pouring out by 5-6K RPM. Initial thoughts from the guys doing the Dyno run was that the oil leaking was from oil return tube or valve cover?


I really don't know what kind of work might need to be done, and I realize it is impossible to tell with any certainty what needs to be done to sort this out...

Any thoughts much appreciated.

Charles Navarro

I would factor in that decision that you are likely going to have to do a teardown and top end rebuild to address the leaks. If you have any concerns about the internals, I'd test the oil and cut open the filter to inspect the pleats for debris.

windsurfar

Thanks again Charles.
Seems like pretty good idea to factor in a top end re-build, and from there who knows, new cylinders? Machine shop work? etc etc.

windsurfar

Thanks Steve.