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Finally, IMS, is this the answer and ultimate closure.

Great information here, thanks :thumbs:

Ok.. so I can remove the 3 bolted cover, look inside and see the bearing and seal. If I were to pull that seal off, (call it the outer) I'd then see the bearings in their case. On the far side of the bearings there is another seal (call it the inner).

I can't see much point in just taking off the outer seal - where is the benefit? Surely it's the inner seal that is key if I wanted to get more oil in the bearing.

Is it possible to get a small drill (by hand) between the bearings/case and puncture the inner plastic seal in several places?

I have no idea what bearing is in my C4 (100k miles 3.4 2000) but am planning a clutch replacement soon so should do something whilst it's accessible.
 
Julian T said:
Great information here, thanks :thumbs:

Ok.. so I can remove the 3 bolted cover, look inside and see the bearing and seal. If I were to pull that seal off, (call it the outer) I'd then see the bearings in their case. On the far side of the bearings there is another seal (call it the inner).

I can't see much point in just taking off the outer seal - where is the benefit?

I think maybe you should re-read the thread.

What do you suppose are the effects of removing that seal... (Considering the bearing is surrounded by lots of oil and a large ims chain drive gear) :?
 
Harv said:
Julian T said:
Great information here, thanks :thumbs:

Ok.. so I can remove the 3 bolted cover, look inside and see the bearing and seal. If I were to pull that seal off, (call it the outer) I'd then see the bearings in their case. On the far side of the bearings there is another seal (call it the inner).

I can't see much point in just taking off the outer seal - where is the benefit?

I think maybe you should re-read the thread.

What do you suppose are the effects of removing that seal... (Considering the bearing is surrounded by lots of oil and a large ims chain drive gear) :?

And where would the swarf go from drilling holes in the rear seal, if you could get a drill bit past the bearing cage in the first place.
 
Julian T said:
Great information here, thanks :thumbs:

Ok.. so I can remove the 3 bolted cover, look inside and see the bearing and seal. If I were to pull that seal off, (call it the outer) I'd then see the bearings in their case. On the far side of the bearings there is another seal (call it the inner).

I can't see much point in just taking off the outer seal - where is the benefit? Surely it's the inner seal that is key if I wanted to get more oil in the bearing.

Is it possible to get a small drill (by hand) between the bearings/case and puncture the inner plastic seal in several places?

I have no idea what bearing is in my C4 (100k miles 3.4 2000) but am planning a clutch replacement soon so should do something whilst it's accessible.

Just as a initial comment, I'd strip the seals off a new one and exchange them, rather than just strip an existing IMSB - you've done the hard work and or expense to get here, no point in not fitting a brand new IMSB! (circa £70)

Anyway, back to you methodology description, yes you can pull the "outer" seal without removing the IMSB, but the engine oil you want access to is on the inner face, and drilling holes is not possible on dual-row any way due to the two offset twin-races (and although possible on single-row, you would be mental to attempt as you could damage IMSB and certainly create debris the other side of the inner seal to be swept around the IMS, IMSB and engine in general), I suspect the drilling idea would not even be very effective in oil flow terms either.

Just pull the IMSB (takes a few seconds) and either strip both seals completely, or ideally fit brand new IMSB with both seals stripped.

Here are a couple of YouTube vids to show how pointless the drilling idea would be:



 
I would be a little more cautious than that.

This bearing provides the end float to position the whole shaft and chain. As you remove the three holed carrier it pulls the IMS towards you and bends the chains.

When the carrier is far enough out to slip off the end of its larger diameter to become loose - the chains both pull the shaft out of the centre line and this can lead to them jumping a tooth and miss-aligning the cam timing.

Undoing the two tensioners can help (one for crank to IMS and one for IMS to camshafts), but any movement of the shaft can pull the chains and they have been used to running on plastic runners and will have created some grooves by now that the sideways movement can chip if you are unlucky or damage the chain link side plates that are brittle and can initiate a fatigue crack later or pin failure.

When you come to replacing the "spider" (the three bolted end plate) you find that it starts to fit the large diameter into the crankcase hole at the very same time the shoulder on the centre shaft runs up against its own shoulder and it is very difficult to pull the centre of the s haft over far enough to get both to engage at the same time and without losing the cam timing.

The standard spindle has a recces in the centre to hold an "O" ring that makes it very weak in bending and while trying to push it over far enough to get the parts to line up you apply side loads that could create a crack initiation and eventual fatigue failure.

Finally the outer spider seal is designed for assembly during 2 halves of the casing shutting together and not sliding into a hole.

If you were also changing the bearing you can remove the old one with a slide hammer (but then need a support to align the shaft so it remains in the right position while you are removing it). The old bearing had a sprung clip best removed with a shock from a sliding hammer but the later circlip retention can allow a puller to remove the bearing.

Using a puller with the old sprung clip can sometimes result in it becoming entrapped and damage the clip groove = engine rebuild.

There is no benefit whatsoever in removing the inner seal - the oil feed is from the outside and inside is just a tube partly full of old oil. If you remove it you need to remove the bearing with the associated problems mentioned above. However if fitting a new bearing it makes little difference if you do or do not also retain an inner seal.

This is all good reason to be reluctant to carry out this work (although we will and do so when our customers request it).

One of the problems for us is that - imagine that by bad luck a chain or tensioner runner broke some time after fitting a new bearing - who is then responsible for a whole engine rebuild to fix it and all the new gaskets seals and lubricants that are essential?

With experience, tools and care failures would be extremely rare and probably the majority of "home mechanics" would be lucky and get away with doing it themselves - but it would just take one failure for a business to regret doing it - because you would need to successfully carry out hundreds of similar repairs to cover the cost of just one going wrong resulting in a full rebuild!

With experience, some special tooling and familiarity with the job - specialists usually carry it out very well but for a one off first time without special tools - I would be very wary indeed. There are plenty of specialists happy and experienced at this job and I would recommend you find one happy to do it for you rather than struggle yourself.

Good luck anyway.

Baz

p.s. before there are complaints about my long answers - just try the job yourself and then feel free to comment.
 
On the basis I would to prefer an old and presumably worn (possibly critically) IMSB to be replaced with a new IMSB, I would strip both seals prior to fitting (it makes no sense not to).

In terms of the space behind the IMSB, every extra bit of "headroom" would improve the prospects of genuine turbulent IMSB wash.

For general reference, here is photo of single-row ex seals:

499251d1293403091-my-diy-ims-bearing-upgrade-and-aos-replacement-old-bearing-seals-off.jpg


And although my previous description may have sounded off the cuff, I do agree the mod is NOT for the DIYer to attempt (not least the cost of the proper tools required for insertion and correct refit outweigh the labour savings)

If time was of the essence, then yes, only pulling the outer seal is better than pulling no seals!
 
What a thread!
I've been away from Porsche for a while but the car still waits patiently for use and attention. That time has now arrived. My IMS bearing was inspected when my clutch was done @ 15 - 20k miles ago (cars on 85k now) when the IMS cover was changed. The local and trusted Indie said it was fine. After reading this thread end to end - and I did, sort of puts things into perspective mostly the input from Baz.
My view is if it reaches 100K then anything after that is a bonus and a rebuild is due anyway due to natural wear and tear. No guesses for where I would have the unit rebuilt.
Baz's statement should go down in Porsche history.
It's been a few years since I drove the car, now where's the rear window washer switch?
 
So i got a 99 3.4 which will have double row its at 72000 miles ...
So its going to blow up or not ? How much to get a independent to pull off front dust cover ?
 
If its a manual wait till you have a clutch change. Should only be an hour or so on top.
 
While this thread has been resurrected I thought it a good place to mention something I saw over the weekend on the Porsche stand at the Festival of Porsche.

Among all the Drivers Selection clothing and usual tat, they had a short engine M96 on show, I was obviously curious as this is my kind of thing. When looking at the IMSB I noticed that this genuine supplied short block had some kind of uprated IMS.

The bearing post is the same thicker type as the Hartech one that is in mine and the nut, that was fairly basic before is now a lot larger and is a flange nut spreading over most of the bearing cover face. I wonder if this is the larger bearing too?

43741452774_33e9d844f7_c.jpg
 
Did you not strip it down and have a look?
 
Dam , Infra how do we find out , I now want to know if Porsche have fixed a problem they wouldnt admit they had and if the uprated part is available to buy seperatly :dont know: and if so how does the price compare with the known aftermarket fixes :?:
 
For a visual comparison to Infrasilver's post, here is my original MY99 3.4 IMS bearing cover:

zb7xYXlm.jpg


The nut and centre is much larger. The case halves casting is different. But the hole the bearing fits in looks the same size.

Looks to me like they decided the centre pin is the thing that needed beefing up. A bearing with a larger centre with the same size outer means the balls are smaller.
 

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