Quote:
Originally Posted by kuehjo
I've been considering your remarks concerning rebuilding and replacing. Please dont take my following comments as critical - I just have a different point of view - and I am open to being corrected if I am mistaken.
I believe that many Porsche owners have the financial means to proceed with a rebuild or replace - but I know some are struggling to financially support their affection for their machine.
NO-ONE wants any kind of debris in their engine or contaminating their oil - but the entire point of the oil pickup screen and filter is to REMOVE these kinds of contaminants before they can damage the rotating assembly.
That said, if the bearing is failing, but the timing has not jumped teeth, in most cases it would seem to me that these engines should be salvageable. The bearing should be replaced, the oil and filter should be changed, and perhaps some version of a flush or a quick oil change (maybe at 100 miles) should be adequate to put these engines back in serviceable condition?
I'm not a Porsche mechanic so feel free to take what I say with a grain of salt, nor do I mean to cause any offense - just offering an alternate perspective - and I might be wrong.... I'm decent at working on my own cars, and I have rebuilt a 928 engine. It just sometimes seems to me that there is the mystique built up about Porsche engineering that is a little over the top - these machines are still just machines. The machine work is just machine work, and the specs are measured as they are in any other engine rebuild. I think Jake Raby's course in engine rebuilding would be immensely interesting and enlightening, but mandatory? Maybe - but maybe not...
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The flaw in your argument about the problem with the grit in the sump is that you are not taking into account how the oil flows in these engines; if you do not get every bit of the debris out of the engine, two engine components are at direct risk: The oil pump assembly and the replacement LN IMS bearing. .
The screen at the bottom of the oil pickup is far too coarse in opening size to even slow down most of the grit, so it gets sucked into the oil pump (look at an oil system schematic for the M96/97 and you will see that the oil goes to the pump first, then to the filter). Because the pump uses very closely meshing steel gears to pump the oil, the grit can either grind away at the gears, or even totally jam them, snapping the already fragile oil pump drive rod, ending any oil pressure. Even if it does not jam the pump, it will abrade the gears significantly (they end up looking like the surface of the moon), reducing the pump’s ability to function. The grit can also jam the pump’s pressure by-pass valve assembly in the open position, further reducing or even ending any oil getting to the bearing surfaces of the crank and rods.
If the grit gets into the new IMS bearing, it will chew it to Hell, just like the oil pump, and it will fail. The rear IMS bearing is splash lubricated by oil from the sump, if that oil still contains debris; it is going to abrade the ceramic balls of the IMS until the inevitable happens. Of the handful of published LN bearing failures, several have been of this type, which is why LN (and Jake Raby) have remained adamant about not replacing the IMS bearing once grit is found in the sump.