We don't just build GT3 engines here... but this is seriously the stuff that keeps James awake at night! If any of you guys also have either a 996 or 997 GT1 based Twin Turbo and are experiencing more engine vibration/noise than you'd think was normal we've unfortunately seen our fair share of this nasty symptom. It's not the same IMS failure you here/read about on the M96/97 engines (that is more common too).


How many degrees of play in that crank shaft?!?! At first you won't even get any check engine lights/codes either. This type of set up is in all the 996/997TT GT1 engines but luckily NOT I repeat NOT in our GT3s- phew. One has to wonder why... The only other thing I can say is of the turbo engines we've seen with this failure there seems to be a correlation of a light weight flywheel into play as well which _could_ be exacerbate the problem due to additional transmitted vibration.

To check for this if you're worried you can rotate the crank shaft back and forth and it it feels loose at all then the next step is to remove the driver's side upper cam cover and observe the relation between the crank shaft movement and the cam shaft movement. Obviously you want to nip this in the bud before it gets bad and leads to a total catastrophic failure.

The noise is most noticeable at idle and when gently increasing the revs to 2000 and then releasing the throttle pedal. It's kind of frustrating that the Turbos don't have the same design as the GT3 but there you have it (or hopefully not!).

 

Very interesting. I got a turbo 2002 and when I look at the GT3 parts catalog for the intermediate shaft there are two different types. 959 105 911 90 timing gear size 0 and 959 105 911 12 timing gear size 1. Can you explain and thanks for the video!

 

Yikes...Alex, is this happening to cars with the 964 lwfw like the one UMW provided me ?
Can the GT3 crank shaft be used on the turbo ? I should stop by your shop so you can test mine...I rather rebuilt now vs. a kaboom motor.

 

could you use that gt3 part in the 996 tt ?

 

im running the same flywheel...

 

I did it because Kevin said it would put less stress on the motor and less stress on the crank shaft... He is very knowledgeable so fingers crossed.

 

Sorry guys on an iphone and at the hospital so I'm a bit limited For sure there are different ways to fix/address the issue so check with your engine builder. This is just one of those things that I would address when building an engine for sure while you're in there. I wouldn't say it's because of a LWF... It's just a poor choice/design on Porsche's part since the gt3 doesn't use this they know how to do it right. I'm just saying if I was worried about this problem it's been interesting to see that the failures have thus far mostly cropped up on cars with a lwf as well. Is it a correlation ? Maybe... It's not as if a lot of these engines have failed but enough to where we know it happens and when doing a build just play it safe

 

Hmmm I think. Here me out; most Porsche owners lug their motor. Which is incredibly bad for the crank on a flat 6 motor, and having a lwfw makes it even worse. I was told by my good friend who owns an older 911, that always keep the RPM's above 3,000 when the engine is warm, always- since before i acquired my car 6 + years ago, and he let me drive his car. I read in the 996 T manual that Porsche states the same. I HIGHLY doubt 95% of the owners out there do this ( this includes GT2's /GT3's) . Specially the Turbo owners, as lets face it, most don't drive a Porsche properly IMO, which looks to be more prone. Yes it is a weak link on the turbo cars though.

Regardless, can I stop by so you can take a look at my car, please !? : )

 

You're right. It's basically impossible if you've ever driven in traffic before. The car clearly likes to be kept in the revs though and will make its discomfort clear when you're running it too low.

 

The GT3 intermediate shaft is machined out of one piece. IIRC, the GT3 shaft costs around $2.5k vs $500 for the turbo intermediate shaft. The bolts backing out is extremely rare. All GT1 blocks engines manifest that rattle at idle when warm eventually. It's just the backlash between the IMS and the crank gear. If the bolts back out on the IMS and the gear starts to wobble you will definitely be able to tell that something is seriously wrong, it would be a clunking sound as opposed to a rattle.

 

I live in Nor.Cal so not as bad as socal. But I can see your point. I know for a fact with my 60,000 miles i have put on my car, 95%+ of them have been over 3,000 rpm, which i can rest in peace knowing i'm driving the car correctly. i.e. above 3,000 rpm when warm.

 

This is a really interesting thread. I've never heard the Porsche advice to operate the car above 3k RPM when warm, but I love it! Now I can forget about saving gas and the additional wear and tear of higher RPMs as reasons to stick with lower RPMs. I for one am ecstatic that I need to drive my car at higher RPMs more often!!!

I'd estimate I run the car above 3k RPM when warm at least 75% of the time since I work from home and don't commute, and rarely drive at rush hour since I hate traffic!

I've got a LWFW, though the slightly heavier Clutchmasters unit than the lighter Sachs. I'd also estimate I'm running about 600 HP/TQ at the crank based on the fact I pull on 997 Turbo S cars in a straight race at the same RPM bands.

 

2000rpm is enough at this point this engine feels good for my experience...

 

Rep points to you Sharky; I also have gone through this problem and addressed it during my EVOMS stage 1 motor build. We brought the intermediate shaft to the machine shop and had it pinned so this can never fail. Well hopefully.

 

Definitely the main reason why I stress to customers to have the GT3 bits(IMS + oil pump) installed during a rebuild. Unfortunately, most just cannot be convinced regardless of what you show/tell them.

I had contemplated looking for an alternative solution to preventing this with the Turbo IMS(IE Tig welding the gear to the shaft) but did not get around to testing to find what the metals were and allocate proper welding procedures for it. It's a problem I think you may start seeing more of down the road here as these cars start creeping in miles.

Good visual there with the vid!