IMS Bearing. To Change or Not To Change (Hear me out)

[Alex]

Does ths post from Baz help

I think you will find that the bearing they are alluding to is the 1204 self aligning bearing (20 47 14) which I would not use in this application with the ability of the main shaft to flex under natural vibration and the weak spindle with the machined out "O" ring recess. It also rates only 78% of the single row bearing dynamic load rating and 51% static load rating (i.e. much weaker).

The original double row baring was a special about which we do not have any technical loadings but from all usual correlations it would be expected to be similar to the single row 6204 bearing.

There is a 4204 with the same O/D and I/D but 4mm wider (at 20 47 and 18mm wide) and this has a better rating than the single row but the narrower double row bearing would have less support area in the ball tracks for the balls to run in and be more in the region of the 1204 which is much weaker and therefore I would guess it would be about the same as the 4204 but needing more modifications to fit it than a narrower one that only requires a spacer to make up the lost thickness.

I guess this is why Porsche used the 6204 to supersede the original double row bearing after tests found it to be better than their original double row bearing (as we have in practice).

The speed ratings are OK for all the bearings mentioned and the two different lubrication systems.

The bearing does normally sit below the oil level and the outer bearing diameter (which is the only rotating part not the inner) will throw oil outwards - however - even lower are the chains (as their sprocket diameters are much bigger than the bearing) and so the oil thrown around by the chains and sprockets is done with more force and volume than the bearing is throwing outwards creating more oil delivery in all directions with high speed and force easily able to get in and out of a bearing that only requires minute amounts of oil in a splash oil system anyway.

If there is a 20 47 14 double row bearing readily available with similar or better specifications - please supply the code as we could not source one! - thanks.


Baz

Taken from here: http://911uk.com/viewtopic.php?t=108552&postdays=0&postorder=asc&start=22

 

[nickyg63]

sorry to not really add anything here, i feel your pain as either way its a tough decision.

you have to keep the car as you have taken most of the risk away now, speak to the guys at Hartech as they are specialists in this field.

The first thing anyone will ask when you come to sell is the IMS, you're into the job is it worth getting an upgrade shaft from Hartech and eliminating any worry and helping future resale value??

I would ask the advise of the Hartech and go from there, its on your mind enough to ask on here.

 

[Griffter]

It's funny that this debate has started again. I thought the pinned post above had largely resolved it: flip the seal when you're in there and live with what you've got.

I understood this was on the basis that, although supposition rather than conclusive, the premature failures are attributed to manufacturing/assembly, meaning the bearing (of whatever type) is too tight, wears excessively creating grinding paste out of the grease/particles and subsequently catastrophically fails. I know the US data showed a higher failure rate for single row bearings, but was that down to different manufacturing tolerances? Or a lower resistance to the bearing being too tight a fit?
In other words is the double row bearing per se a better bearing?

As I understand Baz's post he says the dual row bearing has two smaller bearing tracks, with two sets of smaller bearings. Smaller than the 'small" single row subsequently fitted. In other words it's two small single row bearings side by side, each smaller than in a oe single row bearing. Any load which isn't evenly distributed between the dual rows is going to load one of those rows more than the other (albeit momentarily). I could well believe that all else being equal, a properly fitted single row bearing is better under operating conditions.

We see both types of bearing fail. Is there any reason to suppose the single row is more failure prone today? There are many more about so anecdote may be influenced by that.

Anyway if it was me I'd look hard at engineering a solution to fit the later, larger single row (because it is a widely accepted 'solution"). Otherwise I'd flip the seal of the double row and refit that. As an engineer I quite like the oil-fed solutions (I acknowledge the questions over the supply) but beware of the 'lifed" replacements. Turning the bearing into a service item is not a solution IMO!

 

[berni29]

Hi

Why not just go for the Hartech larger bearing option? Thats what we will be doing on our 996 3.6 project engine. For my own Boxster I just fitted a SKF Explorer C3 cos I had the Tip) gearbox out.

All the best

Berni

 

[Griffter]

Hi

Why not just go for the Hartech larger bearing option? Thats what we will be doing on our 996 3.6 project engine. For my own Boxster I just fitted a SKF Explorer C3 cos I had the Tip) gearbox out.

All the best

Berni

Presumably the bigger bearing requires machining and significant extra expense, which may be difficult to justify?

 

[Alex]

Hi

Why not just go for the Hartech larger bearing option? Thats what we will be doing on our 996 3.6 project engine. For my own Boxster I just fitted a SKF Explorer C3 cos I had the Tip) gearbox out.

All the best

Berni

Presumably the bigger bearing requires machining and significant extra expense, which may be difficult to justify?

The issue is the bigger bearing doesn't fit into the 3.4 end sprocket so a new sprocket has to be manufactured that houses it and fits on an original shaft. Hartech do this but you may find they currently don't have any in stock and may not do due to more important business demands.

I'm sure there's a photo of the different types knocking around but can't find it. This here gives an example:

 

[infrasilver]

You can order the larger IMS/bearing from Porsche, Hartech make their own to the same spec but with the shaft welded to the sprocket instead of it being an interference fit and it's also cheaper. You can only fit the larger IMS with the engine cases apart for reasons Alex mentions.

 

[rgracin]

Some really interesting reads there, thanks chaps.

Still non the wiser, but then didn't expect to be. I'm not sure there is a right answer, maybe just what's right for the individual in terms of what they're comfortable with.

Am I right in saying that all bar the Hartech solution are now suggesting the bearing should be viewed as a consumable and replaced every 40 to 50k?

 

[Alex]

I'm not. Better the devil you know - hence me posting about infrasilver's replacement failing. There's nothing wrong with the bearing that's in there, why change it?

 

[beresd]

I'm not. Better the devil you know - hence me posting about infrasilver's replacement failing. There's nothing wrong with the bearing that's in there, why change it?

That's exactly why I'm not changing mine.

 

[rgracin]

Had a really good chat with Grant at Hartech today. Top chap, thanks for the natter.

Some really sound advice and gives me more to think about. I'll update you once my pondering is complete.

 

[Alex]

Can't fault Grant, Baz and any of the lads there. Star service from them everytime.

 

[rgracin]

Apologies for the radio silence.

I decided to go with the Hartech updated bearing with shaft. For me, it gave the best combination of updated bearing, bolt and cost. I can now build up the engine and forget about it.

I'm not averse to putting a like bearing from a manufacturer like SKF in there but felt I would then need to change it after say 40k (with the potential risks that involves) to give me the same piece of mind.

Highly recommend the Hartech shaft, and the general no pressure chat I had with Grant gave me a lot to think about, but that's what I opted for in the end.

 

[Alex]

Wise choice :thumbs:

You can't go wrong with Hartech.

 

[rgracin]

Starting to build it up now but struggling to find a definitive answer on rod bolt torque.

The workshop manual lists to identical rod bolt specs as 7R both torqued to 20NM but one gives final torque of 90 deg. and the other as 110 deg.

Has anyone found which is correct?

I'm using new genuine rod bolts with part number 997 103 115 01

Any 996 beards out there come across this?