crimony

So a few months ago I fulfilled a dream of mine held for 30-odd years and purchased a Porsche 911, specifically one that I could afford, and that meant of course an early 996. I looked around for half a year or so, and settled on a 1998 model, tip, black inside and out, moderate kms (150,000) a few minor blemishes here and there, body straight though. Test drive was fun (first time in a 911 for me), time to get a PPI. Owner recommended a shop (one of only three in my town), although I got quotes from them all, went with the owner's recommendation. Local independent shop, proprietor a former race driver, builds race engines, Porsches only outfit.
PPI showed new brakes (pads and rotors) required, shocks all round, service overdue. No detailed service records, no evidence of IMS bearing replacement. Compression and leak down were good. Mechanic recommended IMS solution as well if I was wanting to keep the car for some time (I was). Got the owner to knock off a few more thousand following the PPI report and we had a deal.
Brakes and service needed doing straight away so I left the car in the shop to have them done immediately. IMS solution and shocks would take longer to procure so those were ordered but I didn't want to wait. Took delivery about 10 days after the PPI.
Had a blast for the next 4 weeks, not too much though, as I had in the back of my mind the unresolved IMS bearing.
Shocks took a long time to arrive, apparently you need 4, but total stock in the entire country of Australia was 3. Slow boat from Zuffenhausen it had to be then.
Finally I got the call that everything was at the shop, bring your car in. Dropped it off on a Tuesday afternoon, was told they'd try to push and get it done by Friday.
Friday afternoon rolls around, no call so I called. The boss wasn't there but the mechanic I talked to said everything was installed and they were doing some final testing but it wouldn't be ready today.
​​​​​​I gave them all of Monday to sort anything out and called late to get a status. Left a message, as the phone rang out. Tuesday lunchtime came around, no return call yet, now I'm suspicious and very nervous, the boss had previously returned calls very quickly.
Early afternoon my mobile rings, caller id shows the workshop. Boss (owner) tells me with some trepidation that there's a problem. Worse, he won't elaborate over the phone, wants me to come down to the shop to explain, enquires when I might be available. I'm in full panic now, no chance I'd get any more work done until I knew what was happening, so I told him I would leave immediately, 60 minute drive from work to the shop. In a daze the whole way, going over my idea of worst case scenarios. And this is the story that awaits me :
When the IMS bearing was removed, it was a ceramic LN unit. Surprising to the mechanic, as there were no plaques on the car to indicate it had been done. Fine, just fit The Solution and carry on. Solution bearing wasn't quite as tight a fit as the previous bearing, but it went in okay. Fitted, buttoned up, trannie back on, start it up. This is Friday afternoon. Fires up, runs for half a minute, gets very rough, dies. Strange. Check everything, nothing unusual. Check the timing. Out! 10 degrees or so. Retime, try again. Same result. 30 seconds of life, dies, timing out again. Right, check the engine over properly. Spend Monday (boss, not me, I'm still oblivious at this stage) on the phone to everyone who might have seen something similar, everyone agrees they haven't. Heads have been off though.
Conclusion is that the engine has most likely failed catastrophically in the past due to IMS bearing failure, heads have come off, valves straightened, IMS bearing replaced, get the car going again with minimal changes. IMS replacement bearing is slightly larger than the stock, IMS stretched a tiny amount along with the drive (crankshaft chain) sprocket. New IMS solution bearing is slightly smaller and now the drive sprocket is slipping on the shaft.
No doubt about it, your engine is coming apart for a rebuild. While we're there we'll replace the things that you have to and the things you do when you're spending all that labour anyway. Many thousands of dollars expected to be handed over, but we won't know the damage until it's in pieces all over the workshop bench.
Now the wait.

DBJoe996

This is a bad story and sorry to hear things went awry so quickly. I'm sure in retrospect you would agree that it would have been better to leave the IMSB alone. The 98/99 996 engine started life with a very robust dual row bearing with a very small percentage of failure, usually due to lack of maintenance (oil changes). Granted, someone changed out the bearing with the ceramic LN bearing and you can't back trace that work due to lack of records. It could have been original bearing failed, or it could have been replaced preemptively as a precaution since the car ran great for 4 weeks and the PPI found nothing engine related to bring concern. Still, what a mess you are in now. Better hold on to your wallet because this one is going to hurt....

charlieaf92

Terribly sorry to hear that. How reputable is the shop? Dodging phone calls doesn't sound like very trustworthy behavior. I'm also not sure that the story of IMS bearing failure and a quick fix makes sense. You said that car was running fine and passed a PPI - if fixing a IMS failure were simple it wouldn't be an issue.

I'm not an expert, but there are experts here. Hopefully one chimes in soon. The idea that the sprocket is slipping on the shaft sounds suspect to me - and the reasoning is that the LN ceramic bearing wasn't the right size and stretched it out? Not sure if it holds water. Usually the simplest answer is the right one - in this case it was a botched install - maybe they didn't lock the cams when they put it in?

If I were you, I'd call LN Engineering right now. They're incredibly responsive and good to deal with. Explain the situation - and also as if anyone from your shop has called them in the last few days. If not, that is a major red flag right there. If the boss at your shop hasn't personally called LN to discuss the problem, I'd take my car elsewhere immediately. Time to get pro-active to avoid potentially footing the bill for someone else's mistake.

EDIT: the more I think about it - the less I can believe that the bearing would stretch anything enough to cause a sprocket to slip. The tolerances on those bearings are so tight - and if they're off its maybe by microns, not inches. I haven't disassembled an intermediate shaft, but the teeth in the spline for the sprocket aren't that fine.

Edited again - I looked at some pictures and it looks like the sprocket in question may be pressed onto the shaft. If thats the case it would make sense its possible for the fitment to be compromised due to stretching. Best to call LN and talk to someone that knows these things inside and out.

996AE

Something fishy here

318touring

I would have expected that the shop would call LNE themselves. Not just calling around other local shops or in Australia. Never heard something like this before, however LNE would have!

Charles Navarro

No calls or emails on this one. I see every email or support ticket that is created. Unfortunately, this falls into the category that someone installed our product after a failure or did not install it properly. Lack of documentation, even a serial number, would indicate that someone was trying to patch it up. At this point, a complete rebuild is the only sensible option as just putting in a used engine is a toss of the dice.

5CHN3LL

This is the point where I'd bust out the oft-overused-but-still-useful Occam's Razor reference. "My mechanic screwed up" would get a long, hard look from me. Sure, it's possible the car failed catastrophically in the past, and was repaired well enough that you've enjoyed the hell out of driving it for a month - but the car was left in such a fragile state that replacing the IMS bearing has seeming caused serious issues.

It also seems unlikely to me that a seller who is trying to hide (or at least fail to mention) a catastrophic engine failure would send you to the shop that works on the car.

OP, I'm sorry to read about your situation.

strathconaman

I thought slippage of the IMS drive sprocket was a known issue, and that is why LN pinned them. But then again, isn't the drive sprocket on the other end of the IMS shaft than the bearing?

Flat6 Innovations

There's two sprockets, one on each end of the shaft, plus the drive sprocket. These can all spin on the shaft, and I have seen all of them fail at some point.

The IMS Solution bushing is exactly the same size as the OD of a retrofit bearing, or any original M96 diameter IMS bearing. It is NOT smaller. It should fit no more loose than than the bearing that was removed. Period.
If it does, then a bearing had previously failed, and the OD of the IMS Bearing housing bore was effected. This could be from heat during the failure, or grinding/ modification by a hack doing a patch up.

That said, IF this was the case the cam timing would be retarded on BOTH banks the same amount, not just one. BUT this would be the same if the procedure was botched, and wasn't performed correctly.

There's missing links here. I could put this puzzle together if it were in front of me. Either way, it screams patch up/ "quick sell before it blows up on me" loudly.

ZuffenZeus

Is there anyway to know if the shop caused this problem? A vital skipped step as Charlie mentioned?

Ahsai

Yes on slippage. There are sprockets on BOTH ends of the IMS.
OP, really sorry to hear your ordeal and bad 1st experience with 996.

It's very difficult to guess what the truth was without actually seeing the parts but I'm pretty sure the LN ceramic bearing will not damage the IMS if installed correctly. There are tens of thousands of retrofits on the road with no issues.

dan_189

Really sorry to hear your story OP not much in the way of technical IMS advice from me unfortunately but youre in the very best place to get technical advice from some extremely knowledgeable people.

Where abouts in Australia are you? I'm in Melbourne.

Chicago6MT

My stomach hurts for you. Every 996 owner's worse nightmare. Hoping that the damage is somehow mitigated.

Noz1974

Don't go down the road of letting them open up the motor and charge you a fortune, that stuff they telling you about replacement ims being larger and the slippage is not right, get your car out of there !!
Your car wouldn't run for a month with an issue like that, they broke it!!
How much experience do they have on water cooled engines?

crimony

Thanks to all for your support, I appreciate it.
I'll try to address the comments, forgive me if I miss some.
Firstly I remain satisfied that the shop is high quality and know what they are doing, they have a good reputation locally and my interactions with them have been amicable. The workshop is absolutely full of vehicles in various stages of repair, they also have many full restoration projects on the go. I've not gotten the impression that attempts have been made to deceive me, at worst I have felt that the mechanic has been unable to provide a detailed explanation due to himself not having enough information.
Also given my (understandaably) fragile mental state at the time, I am possibly not remembering details correctly, inserting my own interpretations on thing that were said that I did not fully undertand, and have certainly not recalled everything that was said. Some of your responses, particularly Jake's has reminded me of some other possibilities that were mentioned.
Bear in mind that there was only very little information available from the assembled motor, that is:

1. The IMSB was found to be a retrofit, It came out fairly tight but the Solution went in "slightly looser" than previous Solutions that he had fitted. It's possible he didn't identify it as an LN unit at the time, maybe I just assumed.
2. The timing was out, both sides equally, and after it was re-timed, and the engine restarted, it slipped again immediately.
3. There was evidence that the heads had been off relatively recently.

This is not much to go on. I was actually given two choices, with one option to dimple the outer housing of the retrofit IMSB to make it slightly larger, reassemble and hope the drive sproket bound to the IMS. The other option was to strip and see what's really going on. I found the idea of the former option, for a car I was planning on keeping, unconscionable.

@DBJoe996: Yes, in retrospect leaving well alone would have been the best option, but I was prepared to spend the money on what is seen as a reliable preventative measure to avoid a catastrophic failure I'd likely not be able to afford to repair.

@Charlieaf92: The delayed callback I can understand given the set of circumstances, and the need to thoroughly investigate what the cause might be before being able to offer a solution.

@5CHN3LL: Agreed it's a mystery why it would fail following an IMSB replacement task, the myster remains but there is some positive news.

@Flat6 Innovations: That's great info, thanks. As I said above, I'm now not sure if the retrofit that was removed was an LN unit. Your message did remind me that at the time of the discussion of the reason the IMS may have been "stretched" the mechanic did mention exactly what you just said, that the IMSB failure was likely responsible for the effect. Could a special order IMSB retrofit have been made with a slightly larger bore? It's still a mystery why the old one seemed to come out tight and the new one went in looser.

Now's probably a good time to reveal some good news, since you're all in suspense and having read many threads on this site where you guys have to wait around to hear about progress.
All this happened 3 weeks ago, the reason I was able to post this stuff late on a Wednesday night (local time) was that I got a call from the shop Wednesday lunchtime, and visited the shop in the afternoon. With all the doom and gloom I couldn't muster the mental strength to write this stuff down and go over it all again until last night.

The engine is apart (they finally got to it, after finishing all their booked work, of which there is plenty), and it's in remarkable shape. They've pinned the drive sproket to the IMS with 4 grub screws (+ loctite), which should fix the timing slip problem for good. Inlet valves were removed and checked since they touched the pistons when the timing slipped, although they were undamaged. Other than that, the only parts that need replacement are the gaskets and stretch bolts.
Best News: The engine has Nickies, new machined pistons, new top-end bearings, machined billet chain guides and probably many other goodies. Someone has spent a lot of money on this engine sometime in the last 10,000km. Without keeping records. Who does this and doesn't use the receipts to try to get a better price?

Anyway, I realise I'm up for a packet in labour costs, but at least the parts cost will be relatively trivial, and I know that the engine is pretty sweet. It's also true that the strip was required to pin the drive sprocket, so I did the right thing.

Here's some photos I took yesterday (if I can get the attachments to work).

Cheers,

Sam.



Half of the block, crankshaft carrier, IMS (with Solution).




Machined Pistons


The other half of the block, cylinders with Nickies.