Oak

stephan, thanks for the pics. some motors have built engineered "seat" tolerances and once parts have seated wear rate becomes almost nill. this is what I was suggesting. the top and bot bearing show some excessive wear especially the bot bearing it looks to have some galling or pitting. the other bearings don't look too bad.

honestly, I have only heard once very early on about some rattling during startup. I have not heard of anyone having any catastropic problems due to this issue. as you know there are many original high mileage 996tt's running around that still have not mentioned rattling at start-up. could this be an issue with just the early engines?

PorschePhD

Not in these motors. You can measure them when they come out of the car and will make you fall over.

I haven't done any 04 motors, just 03 and down. So I can't say if the 04 have the same premature wear issue. I suspect that since the spec is the same accorss the board that it will not make a differemce. I had also talked with a freind that does GT3 Cup car motors. He too has seen the same wear.

strato58

How does Porsche get away with this crap? $125,000 car and its got this design flaw! I thought they were suppose to be a superior engineered car. Im far from an expert but to my layman eyes that is an incredible amout of bearing wear on a car with 6500 miles!!! What happens at 65,000 miles???!!!

FixedWing

I have been taking oil samples on my engine since it was almost new and have noticed some metal levels that were consistently slighty above what I would have expected despite an excellent running environment. I think this could explain a lot of that.

Stephen

Wachuko

Innocence is bliss… now I know...

It is better to know, but it is like a hero has fallen... argghh... I was really looking forward to buying a second hand 911Turbo... with the higher production volume of the 996TT and how prices are going I thought it would be the logical choice. Now this...

Thank you Stephen for your insight into the problem... hopefully you will come up with ways to minimize it and share them here.

PorschePhD

For me I just keep driving it and keep watching. I do think that one will still get mileage 100K out of the car. Look at it like the old 930 and Carreras, at 50K-100K you went in to do the heads since the guides were almost always shot. Many 993 owners ignore that fact, but most are in the same boat. I consider it an issue, and have known for a while. Mass Hysteria? Nah more like an issue and one that would prompt you to change your oil sooner than 10K miles!!

vyper340

Use one of those oil filter magnets to add in the capture of errant metal... I use them on my boat high HP engines and they do capture extra stuff.

1999Porsche911

The use of 0w40 oil in hot climates is coming home to roost. Wait until the main bearings start to fail.

m42racer

Stephen,

Any chance you could post another photo of both halves of the rear main, together, showing both thrust faces. From what is show on the 1 half, the problem "appears" not to be from too much, or too little clearance. It would be really evident if both shells are together showing both thrust faces.

Thanks for the info, really interesting stuff.

Premier Motorsp

I think that problem is the result of the additional load on the intermediate shaft from the extra cams. The intermediate shaft gears are helical cut so some of the torque going thru those gears gets turned into a thrust load. The crank gets pushed one way and the intermediate shaft goes the other way.

You don't see this on a 993 Turbo engine, which has the same bearings, crank, case, intermediate shaft, etc. So it can't be the clutch switch causing the problems.

On all the 996 Cup engines (which is exactly the same as a Turbo engine) I have had apart the intermediate shaft thrust bearings looked pretty worn. The crank thrust bearings looked a little worn too but I am used to seeing this on engines operated at high rpm all the time. These engines tend to have the big wipe mark on the face of the bearing where the main journal runs, but not the down-to-copper wear on the thrust surfaces.

I don't think there is any fix for this. When the engine is first started, the drag of four cams and 24 valves loads up that intermediate shaft gear and the thrusts are taken by the bearings before an oil film is established. The result is wear.

The oil viscosity shouldn't be an issue. The wear must be occuring before the oil film is established. This is an interesting design 'feature' but I can't imagine this ever causing a failure.

Chris Cervelli
Premier Motorsports

cjv

Stephen,

Would coating the bearing help any?

TT Surgeon

Slightly OT, Stephen, are you guys doing anything with na m96 motors yet, and do they show this wear as well?
TIA

m42racer

Chris,

I think the extra load will put more thrust on the rotating parts, but the 959 is similar and this engine did not have this problem. Although other 4 Cam engines were gear driven, and had straight cut gears, this problem looks unique to this engine. I do not know of the 959 had straight cut gears or helic. Maybe you you know.

I still think looking at the photo of the Rear Main shell, the problem is evident. Seeing the other half would verify the problem.

If it is what it looks like, Oil type, coatings or other bandaids will not fix the problem. I agree with you its definitely not a clutch induced problem. It is also not a design fault.

If its possible to see both the rear main shells showing the Thrust faces, that would be most helpful.

If it is what I think it is, those that have been inside these engines and not seen what appears to be the cause, either have missed it by not checking a very critical dimension or not studied the result of the problem that appears in the photo of the bearing shell.

PorschePhD

Simon,
I will dig the rest of the bearings up. I am trying to finish up a couple of projects and get a TT out the door for a track event this weekend. I have the customer here while we are tuning it on the dyno. As soon as I get a moment I will grab them. I just have to dig for the other halves.

Coatings will not cure the issue. Any coating will come off. The clearance is to large I believe to coat any way. I think that you will find that even if you called the dealer they do not spec out the cranks like this. When you go to look for the spec of the thrust clearance you will not find one. Every motor I have done was almost identical. If you call around most don’t check this because they assume that the crank is ok on a new motor. I literally was told several times “heck, I don’t know I never checked it” Being the worry wart I am when building motors and the fact I blueprint most of them the spec was way out of whack compared to the 930 motors I had done and even the 964/993 stuff. I became alarmed by the constant wear on the motors with mileage ranging all over the map. The wear and the spec way almost always the same. Chris is right that also the intermediate shaft bearings also take a beating. The drag on these motors is huge. Simply put of you spun the motor with no accessory on it compared to any 993 motor you would swear the bearings were oval. I personally can still not get an answer out of anyone on why the loose spec. Porsche sure isn’t telling their guys. Other things that have gotten a little loose is cylinder specs. Anyone actually check these yet. LOL, there is not one cylinder I have checked is actually round. I am constantly amazed these days.
.

ebaker

I wonder if using Redline oil (very high moly) or adding General Motors EOS (very high ZDDP) to Mobil 1 would be helpful?