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

Going back to my comment on oil level compared to the IMS bearing position and wanting to prove my (educated) theory correct, today I got a spare crankcase half I had lying around, like you do and got the tape measure out, I measured the engine oil dipstick tube from my 996 and deducted this length from the the length of the dipstick. I dropped what would be left of the dipstick into the same line the dipstick would run, give or take a few mm. I used a straight edge to show the line at the top of the IMS opening the results are below.

I took some pictures and you will see the upper oil level mark on the dipstick is about level with the top of the IMSB cover opening meaning the bearing which is much smaller than this hole is deep into engine oil if you keep the engine topped up to the brim as I always do.




Straight edge in white going from top of IMS cover opening and passing through the top level of the dipstick.







Obviously engine oil, once the engine is running is spread around the engine but there is always a good quantity in the sump still and easily enough to lubricate the bearing as it really does only require a small amount to lube it.

Using these pictures and my two previous together and hopefully that answers a few questions once and for all.
 
I can 100% confirm that the bearing sits in oil (after my man forgot to drain it). As soon as he undid a cover plate bolt, the oil started to pour out :grin:
 
And make sure there is not a customers car close by when you take the IMS cover off if you haven`t drained the oil

:floor:

 
infrasilver said:
Using these pictures and my two previous together and hopefully that answers a few questions once and for all.

Great work that man, I've often wondered where the oil levels came to inside the case at max and min on the dipstick.

Like you I always keep the oil level topped right up :thumb:
 
:thumb:
 
I used to work in cleanrooms (for Philips manufacturing CRT cathodes - 500,000/day), which meant dry bearings on all the equipment. Due to them all being frictionless bearings (like the ims bearing) it was possible running 24/7 and they lasted for months. Folk don't realise these type of bearings only need a bare minimum splash of oil to make them last foreve (unlike solid bearings). Don't know what Porsche were thinking putting a sealed bearing in an oil bath :?
 
Having looked at a few dismantled M96 engines at my indy's place, doesn't the real problem lie with the narrow width of the connecting shaft that inputs into the IMSB. That shaft ought to have been thicker. Then when a bearing fails as some always will (it's a part so some will break) the shaft won't break and cause havoc as happens commonly now.

Sure bits of disintegrated ball bearings floating around are never good, but at least all the connected bits would still be, er connected until repair? Surely it's in the lack of designed in inevitable failure where the design went wrong? And that's not something that arises from cost cutting. That's from bad judgement and incompetence.

If the Harris case had pushed that angle more Porsche would've had a real global problem I think. Having read the papers from that case I often wondered if it was a fear of that angle of attack that made them settle so easily :dont know:
 
It's not the bits from the bearing floating round the engine that do all the damage (although they'll do some). Once anything breaks with regards to the ims, it throws the cam timing out, which then leads to overcrowded boxing match between 6 pistons and 24 valves (imagine the carnage after that).

I must admit, I was quite surprised at size of the spigot that supports the bearing . The undercut at the end of the thread must only be in the region of 8-9mm in diameter, supporting a large shaft with 5 chains running 4 cams off it. :nooo:
 
alex yates said:
It's not the bits from the bearing floating round the engine that do all the damage (although they'll do some). Once anything breaks with regards to the ims, it throws the cam timing out, which then leads to overcrowded boxing match between 6 pistons and 24 valves (imagine the carnage after that).

I must admit, I was quite surprised at size of the spigot that supports the bearing . The undercut at the end of the thread must only be in the region of 8-9mm in diameter, supporting a large shaft with 5 chains running 4 cams off it. :nooo:

Exactly. That's my point. (I abbreviated the above to 'connected'!) The width of that shaft would have been discussed I'm quite sure with regard to acting as a fail safe for the inevitable failure of the bearing (at some point). Someone either decided that the failure would be so rare that it wouldn't matter, or to ignore that additional level of fall back. The width of the shaft could easily have been doubled in size. So why wasn't it? That's the question I suspect Porsche don't want asked.

It's a bit like the water cooling flaw in the larger bore engines. Surely someone asked questions internally? :?:
 
The shaft I have from Hartech is a lot thicker than standard and I recommend getting it changed if you change the bearing. The standard one can get weakened by removing the cover and re-tightening, it's still a known weak point, sometimes overlooked.

 
I would've deffo done that if I was removing the bearing. The fact that OPC scored all the seal on one side of the plate refitting it put the frighteners on me.

I'd probably make my own if I did one with something like an M18 thread on with no undercut.
 
Do you think the mileage estimates on bearing failure probabilities vary much with age, and if so how? Surely a car that does 50k over say 4 years will have a very different effect on the grease displacement etc that one that does 50k over say 10 years + ?
 
The view of Road & Track Magazine. More odd 'stuff' on the IMSB - e.g. "a short run of low capacity bearings, 'some' of which ended up in early 996's."

"The biggest reason for low 996 values is the misconception that the engines have the durability of blown glass. This is one gripe with the 996 that really needs to be addressed. Some early cars featured a weak bearing in the intermediate shaft, known as the IMS. Porsche has used an IMS in its 2.0-liter engines since 1965. The IMS drives the camshafts indirectly off the crankshaft. But even before the introduction of the 996, Porsche had experimented with new bearing designs, and this development resulted in a short run of low-capacity bearings, some of which ended up in early 996's. An IMS bearing failure results in a completely destroyed engine. Luckily, most qualified Porsche shops can perform a pre-purchase inspection and identify bearings that have been upgraded or may need to be replaced.

As terrible as a blown engine is, enthusiasts have made it seem like every 996 came with a defective engine. Further fanning the flames, Porsche's handling of the problem was a PR disaster. But the reality is that the majority of the engines are fine. "Engine failures in [engine model] M96 in actual real numbers range from one to five percent," Brownell says. "It's more than there really should be, but it's not quite as dire a situation as the Internet would have you believe." What's more, the problem can be corrected by a $400-$700 upgrade."
 

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