Need help w/Engine knock solution

I picked up a 2001 911 C4 with an engine noise that sounded just like a failed IMS bearing. Began IMS replacement with engine in car. Pulled IMS bearing. Old IMS bearing does not look or feel bad. Here is my question - Do I install new bearing at this point? Or drop engine and look for another source of the noise. I was expecting to see a noticeably bad bearing, one ready to fall apart but this one looks and feels good. Any ideas?

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Not to put too fine a point on it but it is a good idea to as best you can pinpoint the source of the knock noise before you attempt a repair to address the noise. If knock describes the noise fairly accurately a knock can be from a number of causes, from a bad water pump, to a bad rod or main bearing, the manual gear box, even a loose converter brick in an exhaust manifold, to name a few of the possible explanations. If you have the old bearing out I would replace it with a new bearing. Replace the RMS too. Be sure you do not put the new one in at the exact same spot at which the the old one was located as this can have the new seal leaking in no time. I'd be tempted to button the engine up and then work on pinpointing the source of the noise. If coming from deep inside the engine cases then dropping the engine is probably your next step. But you may find the noise coming from some other location and you may find the source of the noise is not directly related to the engine at all.

Macster - I am inclined to put everything back together and recheck. The noise sounded just like the descriptions that I read/heard of IMSB failure. Definately coming from engine, rise and fall with rpm. I guess what am wondering is if it's really possible to tell, just by looking at the IMSB, if it is failing.

I HAVEN'T HEARD ANYONE SAY A KNOCK WAS THE SOURCE OF AN IMSB. ITS USUALLY DESCRIBED AS A RATTLE ON STAT UP.

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If (if) the noise was from the IMSB you would be able to tell the IMSB was failing. The bearing would have excessive play and the seals would be deteriorating. It could be bad enough, far enough along one or both seals would be gone and the cage nearly gone and the thing just a minute or less from catastrophic failure. When the IMSB bearing gets real noisy it hasn't got but seconds to live. What's the oil filter housing oil and filter element look like? Any scary debris present? Be sure you pour this oil out into a *clean* drain pan. The noise doesn't have to be from the IMSB -- my WAG is it is not -- but it could be from a falling tensioner or perhaps a failing guide or rail, assuming the noise is from that part of the engine. Without hearing the noise I can't really say. Even hearing the noise might not be that helpful. And I'm not hinting you post an audio of the noise. The less engine running you do until you get the noise nailed down and its cause addressed the better.

Sorry, life got in the way. I decided that it would be best to drop the engine and rebuild. Not a lot of spare time but have managed to get the engine on the table, ready to take apart. This will be my first 996 engine rebuild. Anyone have any tips and/or concerns? Ordered the Bentley manual. That should have all torque settings? Thanks for those that took time to comment.

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If you can find them the 996 factory manuals (in PDF form) are recommended. However, even these do not include some pretty important info. There have been some 996 engine rebuilds and threads on these have appeared here. While I generally do not like to suggest someone go search for the info he seeks, since I can't recall verbatim the details of an engine rebuild (and couldn't vouch for its accuracy/correctness even if I could) my advice is you search for these threads. Some have links to photos and even videos that deal the rebuild steps. Read them all, view all the photos, and videos, and take notes so you have a clearer picture of what it takes to tear down and put back together one of these engines properly.

well, I finally got the engine completely disassembled. Here's what I found. It's off to the machine shop. Oh, and you were right about the Bentley manual. I didn't think it was worth the money either.

did u have intermix?

No. When I bought the car, it already had the problem. PO made some attempts to repair it. I am sure the oil was changed previous to my purchase. Coolant looked new, I am sure that was changed also.

You may find it useful to search for"scoring". There have been some suggestions that it may be caused by low temperatures and Western NY State would get those. The theory is that when started at very low temps, the forged pistons expand much faster than the cylinder bores. The clearance is too tight,the oil boundary layer fails and scoring occurs.0w-30 oil may(??) help but the advice is to avoid starting the engine in very low temps to prevent risk of scoring. Not saying this is your situation but worth investigating perhaps.

Schnell Gelb - Thanks for the suggestion. I would like to know what caused this, obviously, to make sure it doesn't happen again. The vehicle has over 100k miles and I recall it spent many years in Arizona. I will continue to do research but wondering if/how anyone has made this repair in the past.

I'm not an expert,so I am not offering a competent diagnosis. But this may help you to refine your Search : https://rennlist.com/forums/996-foru...cylinders.html " In Canada the only way to avoid it is not to drive the car at all in winter. Note where the guys are that have these issues and you'll see the same common denominator over and over. The factory did not allow for adequate running clearance in cold temperatures with these engines, especially those that have forged pistons. After being just started the piston expands faster than the cylinder and the clearance becomes too tight, which makes it impossible to gain boundary layer lubrication from the engine oil. To make it worse, the oil is still cold and thick when this occurs as its only seconds after cold start up. Cayenne engines have the same issue and its so bad that a couple of Canadian dealerships send us their engines rather than installing a crate engine that will just do the same thing all over again. One Cayenne owner has had this occur 4 times! We have done much more of our testing in super cold, than in super hot. Next month we'll have a test car start a 20,000 mile loop of N America. I wish he was on the road now, taking advantage of all these awesome opportunities to see single digits and below zero values. Then we'll take it apart and see how it looks. The record on one of our test engines is 5,200 cold start cycles. If you have to drive in the cold try to keep the car stored in a warm environment and when driving down stay parked so long that the engine completely cools down! __________________ Jake Raby Flat 6 Innovations"