Oiling trouble on the 928 seems to be related to high rpm in turns, air getting into the oil stream. Nobody has any trouble with straight line high rpm, so what is the point with drilling the crank? I can't figure out how it makes any difference to a G force related oil issue.

 

Getting ready to change my rod bearings in my 968 at 125k miles... pre Carl Fausett supercharger.

 

Cool.

 

does just buy alittle xtra time under g stress..?

 

IIRC the issue for non-g-loaded rpm is

- that at high-rpm the stock crank starves the 2/6 bearing no matter what you do

AND/OR

- at high-rpm oil foam is pumped to all the bearings and the 2/6 dies first.

That's my recollection. Waiting now for folks that really know to come along....



EDIT: 928s have died under sustained high-rpm conditions due to 2/6 bearing failure. IIRC this is almost-exclusively a phenomenon reported from Germany - where they have roads that allow them to run flat-out for many minutes at a time.

 

If you do not track it there is no need.....

 

This has been flogged, at length, in this forum. Search, my friend.

 

Flogged yes, illuminated no.

Tried search, may use the Visit function tomorrow.

BTW I actually think I understand the physics, pressure, rpm, etc., which is what led me to the question why bother? Its a high rpm fix for a G force issue.

 

Um, no. As mentioned above, engines have failed after prolonged high speed straight line driving on the Autobahn.

 

I laughed out loud at that one.

 

the poor oiling system is the achilles heel of 928's......sure timing belt & thrust bearing failures get more attention....but the bottom line is if you plan on operating the 928 engine at high RPM....you better upgrade it....... I've proven this THREE TIMES

 

Given the Euro gearing I would think every 928 that has been on the Autobahn or any other high speed opportunity has been driven significant amounts at high rpm, nobody is screaming, so we must be talking about rare occurrences that may or may not have other circumstances besides high rpm worth considering.

The 2/6 bearing does seem like where problems show up, but that doesn't mean fixing the 2/6 is a preferred option to fixing the root problem of air in the oil.

 

(4 )928 engines with no mods have been race more than any 928 engines out there, and no issues. I wonder why? Oh yeah, that has been discussed already too.

(i.e. scots 4.5 liter, scots 5 liter, my US 4.7 liter, my 5 liter part euro , and the holbert engine which had 5000laps alone!)




mk

 

I don't think it is a G force issue in the sump. It is a centrifugal force issue, as the oil has to travel the wrong way against the centrifugal force of the crank spinning. Cross drilling is supposed to redirect the flow so as to go with the direction of the G forces of the spinning crank. High RPMs = higher G force = oil starvation.

Oil starvation is a separate problem as I understand it.

Someone correct me if I am wrong.

 

You got it.

Porsche had to completely redesign the cranks for the 944GTRs, because of this problem....once they started running them at higher rpms. They are "surface" drilled, not "center" drilled.

Part of the reason that Kibort has had so little problems is that he has limited the rpms on his engines. He doesn't go near 7,000rpms.