Yes a plain bearing (as fitted to earlier 911 variants up to M96 engines) has a pressurised oil feed which all plain bearings need but the ball bearing in the M96/97 IMS can be exposed to plenty of splash oil if the seal is removed.
Oil does seep in if the seal is still there - it can hardly be called an oil seal - OK for dust and thick grease perhaps - but someone seems to have forgotten that the engine temperatures inside would turn the grease thin like oil anyway and eventually seep out.
The shaft is hollow and eventually can fill up with very old smelly and probably carcinogenic oil through the leak in the inner seal.
The inclusion of the seal could be connected to manufacturing storage time as a grease filled sealed bearing has longer shelf life than an open unsealed one? Don't forget the new boss brought in to transform Porsche financially had a washing machine manufacturing background!
All they had to do was pull the outer seal off during assembly! leave the existing grease there and allow it to wash out during running in to be replaced with fresh oil.
The smaller bearings have too thin an outer track to prevent the interference fit from altering the pinch between different shafts, spindles and bearings when the tolerances stack up for a tight fit. The larger bearing has a much stronger thicker outer casing and of course does not require a tighter fit - so sustains the designed clearances better.
On diss- assembly some housings and outer bearing diameters in the smaller bearing show signs of "pick up" during assembly or running and pushing another new bearing in without measuring the housing and correcting any errors can lead to further problems down the line. Bearings have different fits (or tightnesses) in their design and manufacture and we chose a replacement bearing with more clearance to compensate. We may replace a larger bearing on a high mileage engine during reassembly and have not seen "pick-up" there.
Feeding oil from a pressurised feed will not deliver it into the bearing under pressure - just flow - and if it is high flow it would starve/reduce the engine oil delivery on hot tickover when the pressure is low anyway and well below the relief valve setting - so there is nothing you can do about it. Whereas as soon as an engine starts there is a massive amount of oil splashed into the bearing area - after all - if you want some proof - just consider that a high mileage car with the seal still in place and the bearing still OK has managed to lubricate sufficiently after all the grease has gone and just relying on the tiny amount of oil that is managing to splash into it past the slightly worn seals - not being replenished and therefore running hotter than the main oil supply! What more evidence do you need that splash oil without the seal restricting it - is adequate?
Baz was just wondering when you choose a smaller bearing with more clearance how tight a fit it was and whether you use any retaining compound.
Also is there anyway the seal can be dislodged engine in situ.
(1) The difference in bearing sizes/fits I referred to is not the outside diameter or the interference fit in the housing but the basic clearance between the inner and outer track and the ball bearings. If the bearing is too precise and the fit too tight it can lead to premature wear so the right bearing choice and specification is important.
(2) Ball bearings work better with splash oil than to be flooded in oil as the sheer in the oil is higher with too much flooded oil and there are also power losses with too much oil supply. The best supply is just splash oil - which the continual supply of splash oil from the chains and the sprockets running close by in an oil bath provide while the centrifugal forces of the spinning outer bearing clear out enough to allow the bearing to run with splash oil as both intended and best for it. Hence most ball bearing applications being exactly like that in engines and gearboxes successfully for decades.
I am from Croatia and my center knows a little about the IMSB failure just because of the small number of M96/97 engines . The only couple of the bearings failures were due to overtightening the nut on the flange to prevent IMS oil leaking (they didn't respect the manuals torque specs) so the bearing fails .
I have an early 2005 997.1 C2 Tip with 108k kilimeters on it (about 67k miles) , regularly maintained , dry engine , uses no oil , great car/engine. Use Mobil 1 0w40 from the day one. My engine number says it has a smaller changeable single row bearing . I would like to remove the seal from the bearing but it is a tiptronic so no clutch to change and it would be a costly job just do that.
My question to Baz and everyone else who comprehand my question :
Will I gain some better lubrication on this ball bearing and longer life by letting the oil in the shaft from the opposite side , by the oil pump drive ?
I mean removing the oil pump cover and the gears , punching a small hole on the IM shaft plug , installing a retrofited sloted hex gear to feed the oil in the shaft. In my case all the seals on my original bearing will stay as is.
I reckon the oil will get in the shaft by pressure and slowly go through the bearings seals out back into the sump. So there will be no forced high pressure oil on the bearing like some IMS solutions because the bearings
seals would protect it. The other question is would this situation make the oil go back to the pump more than go through the bearing and make the oil pump work harder and lower the engine oil pressure ?
This is a low cost and easy procedure thats why I ask.
There is a seal both sides of the IMS bearing so any oil the other side will just sit there the same as the other side and not really penetrate the bearing. There is also the issue (unsure how critical) of the oil pressure you may loose from the pump to the engine if pumping oil into the IMS when punching a hole at the pump end.
I know there are two seals but the oil go through both seals by time and oil attacking it for years and seals are no more tight. If the splashing oil goes through both seals and end up in the shaft from one side , why would'n it go from the shaft outside, towards the flange ?
The shaft oil pressure is the question I reckon.