996tt MY2002 timing chain failure

[AngelOfGrief]

Hello.

 

Recently I was driving the car as usual and suddenly PSM light went on, then the check engine light, then the engine shut down. I tried to start it but it wouldn't. After several other attempes the engine stopped turning. :o I had the car towed and today took it to the repair shop. Diagnostics showed timing errors in camshaft 1, so the tech removed the left cover to find the timing chain broken. It must be mentioned that I had the infamous 996tt chain rattle, but I kind of thought it was "normal". Turns out, it wasn't...  <_<

 

Now, we're up to two options:

 

1. Try to replace the timing chain without tearing the engine apart.

2. Remove the engine from the car and take it apart to see what's actually damaged inside the engine.

 

Whilst the tech decides which way is better, I am up to buying the timing chain. So, the original part no. is 99610555271, however, there is an OEM part from Iwis, as pelicanparts.com suggests:

 

http://www.pelicanparts.com/cgi-bin/smart/more_info.cgi?pn=996-105-552-71-M48&catalog_description=

 

The Iwis part is really inexpensive. So, after some googling I was able to find the Iwis part no, it's D67ZN-19. Then, I found this document:

 

http://www.iwis.de/uploads/tx_sbdownloader/iwis_Motorsysteme_Automotive_aftermarket_Ersatzteile_DE_EN.pdf

 

So, if possible, could someone please kindly answer these questions for me:

 

1. Iwis chain comes without the master link, which means it can be replaced w/o tearing the engine apart. How do I order the master link? What is the part no?

 

2. Does the original timing chain come endless or without the master link? Searching for 99610555271 in google images suggests it does not come endless, however, the oem part in the engine IS endless:

 

3. The part no. D67ZN-19 according to the PDF above translates into several car models, including 996 carrera, 986 boxster, 996 GT3/GT2/Turbo, even some Mercedes and Peugeot cars. Do these cars really have the same timing chain or is it some kind of error?

 

YOUR HELP WOULD BE GREATLY APPRECIATED. Thank you!!

[JFP in PA]

Hello.

 

Recently I was driving the car as usual and suddenly PSM light went on, then the check engine light, then the engine shut down. I tried to start it but it wouldn't. After several other attempes the engine stopped turning. :o I had the car towed and today took it to the repair shop. Diagnostics showed timing errors in camshaft 1, so the tech removed the left cover to find the timing chain broken. It must be mentioned that I had the infamous 996tt chain rattle, but I kind of thought it was "normal". Turns out, it wasn't...  <_<

 

Now, we're up to two options:

 

1. Try to replace the timing chain without tearing the engine apart.

2. Remove the engine from the car and take it apart to see what's actually damaged inside the engine.

 

Whilst the tech decides which way is better, I am up to buying the timing chain. So, the original part no. is 99610555271, however, there is an OEM part from Iwis, as pelicanparts.com suggests:

 

http://www.pelicanparts.com/cgi-bin/smart/more_info.cgi?pn=996-105-552-71-M48&catalog_description=

 

The Iwis part is really inexpensive. So, after some googling I was able to find the Iwis part no, it's D67ZN-19. Then, I found this document:

 

http://www.iwis.de/uploads/tx_sbdownloader/iwis_Motorsysteme_Automotive_aftermarket_Ersatzteile_DE_EN.pdf

 

So, if possible, could someone please kindly answer these questions for me:

 

1. Iwis chain comes without the master link, which means it can be replaced w/o tearing the engine apart. How do I order the master link? What is the part no?

 

2. Does the original timing chain come endless or without the master link? Searching for 99610555271 in google images suggests it does not come endless, however, the oem part in the engine IS endless:

 

3. The part no. D67ZN-19 according to the PDF above translates into several car models, including 996 carrera, 986 boxster, 996 GT3/GT2/Turbo, even some Mercedes and Peugeot cars. Do these cars really have the same timing chain or is it some kind of error?

 

YOUR HELP WOULD BE GREATLY APPRECIATED. Thank you!!

 

I think you are misunderstanding terminology here.  The Pelican chain, "without a master link", is an endless chain that requires pulling the engine out and apart to change it, as does the factory chain.  It is also not uncommon for some parts to fit many different brand vehicles.

 

In any case, having worked on Turbo's for many years, I really don't see how you are going to change one of these chains, even with one with a master link, without pulling the engine.  These cars have very restricted space around the engines, making pulling the engine a real time saver for many such repairs.

[AngelOfGrief]

Thanks for the answer. Yes, in fact, we decided to pull the engine and take it apart completely to see what was actually damaged. From what I could find on the net, a broken timing chain may cause severe damage to many engine parts: valves, sprockets and even the IMS, in some cases. So, I guess, it's gonna be a complete engine rebuild, once again. Ah, well...

[Silver_TT]

By way of clarification, the rattle of the chain at idle is normal and is that way on every 996TT I have ever seen so I don't think is in any way inherent to your problem.  It's more coincidence than causation.

 

Yes, if the timing chain snapped (which I have never heard of on a TT before) is it possible it could cause damage to the engine since the timing would be completely off.

[AngelOfGrief]

Well, we have several 996tt's here in our local Porsche Club, but my chain rattle was much louder than on other people's cars. It's actually a long story, my engine was rebuilt about 3 years ago (due to IMS sprocket failure) and developed this rattle after the rebuild. Before the rebuild the chains were perfectly silent. The tech person who worked on the car and also many forum postings presuaded me it was normal, so I drove the car like that for 3 years, and now, here we go, chain failure. <_<

Edited June 24, 2015 by AngelOfGrief

[AngelOfGrief]

Today the engine was disassembled completely.

 

Apart from the timing chain torn, we have 6 valves damaged, IMS sprocket teeth bent and broken (the sprocket which was carrying the broken chain), plastic chain guides worn. No metal parts inside whatsoever, no metal in the oil filter. What's much worse, there is no indication of what caused poor chain tension condition, so the tech guy is kind of clueless. He checked the tensioner and told me he believes it's working. The tensioner is sill under suspicion, but the price is sort of unreasonable (95910505101 - around $400), I don't really know if I should order it along with other parts.

 

It kind of makes sense to replace everything related to timing mechanism: chain, tensioner, sprocket, guides. But from my experience, the "replace everything" method does not work in 80% cases. You have to find the real cause, and eliminate it. Otherwise, it's a waste of time and money... :(

 

If anyone has any ideas, please kindly share.

[Silver_TT]

Ya, with all problems you really have to find the real cause so you can eliminate it, just like you said, otherwise throwing parts at it can get expensive quick with the price of OEM parts.  Hard to really say much since I don't really know much about your car and you said the engine was rebuilt a few years ago.  But that engine is one of the most solid Porsche ever made and has no true flaws to speak of.  I find it difficult to comprehend that this is basically the second seemingly similar failure you've had in 3 years with a Mezger engine.  Not saying it's never happened before but yours is the first I have ever heard of a Mezger timing chain just snapping -- definitely seems like something else is off but I don't know if the engine was modified or what was done to it during the last rebuild.

 

I'm not surprised the values are damaged since the timing would have been completely off when the chain snapped.

[JFP in PA]

Today the engine was disassembled completely.

 

Apart from the timing chain torn, we have 6 valves damaged, IMS sprocket teeth bent and broken (the sprocket which was carrying the broken chain), plastic chain guides worn. No metal parts inside whatsoever, no metal in the oil filter. What's much worse, there is no indication of what caused poor chain tension condition, so the tech guy is kind of clueless. He checked the tensioner and told me he believes it's working. The tensioner is sill under suspicion, but the price is sort of unreasonable (95910505101 - around $400), I don't really know if I should order it along with other parts.

 

It kind of makes sense to replace everything related to timing mechanism: chain, tensioner, sprocket, guides. But from my experience, the "replace everything" method does not work in 80% cases. You have to find the real cause, and eliminate it. Otherwise, it's a waste of time and money... :(

 

If anyone has any ideas, please kindly share.

 

As Silver_TT pointed out, you have a now rare and very precision built, low production numbers engine, so some of the parts are not going to be cheap; but even so, I would not hesitate to replace that tensioner and everything else on that chain side. 

 

We regularly see a number of these cars, many of which get the daylights beat out of them on a regular basis; and I have never seen this type of issue with the Mezger engines.