svp928

Right, Dave, if its pumping aerated oil, it will fill the accusump with it also, and I think the aerated oil and windage is a bigger problem than than slosh moving oil away from the pickup. A dry sump eliminates most of the aeration, but windage is still important, as Louie and Greg have pointed out.
On a wet sump with good windage control, and accusump will help if the pickup gets uncovered.

Fabio421

It looks like a low pressure accumulator to me. Is it a bladder or piston style? The picture looks like a piston style. What is the charge pressure? What is the oil volume?

Fastest928

Your statement is a comment based on another engine builders comment and had nothing to do with porsche 928 ranks and rods.

"make sure the rod bearings clear the radius on the crank(chamfer if necessary)"

Like I asked: What are you talking about?

Plastigage is good stuff to see if you are in the ballpark....using it as the final measurement is for weekend warriors, not pros.

Marc

Fastest928

Dennis system also uses the system 1 filter with bypass in case of filter clog. Later we switched to the "nascar" fram filter with a Peterson take off plate to increase the filter area. This system saved Don H engine after he ran it out of oil.

Marc

SharkSkin

I don't know the details of how much oil should be allowed for windage, but you're right -- that's a point of concern. Also, getting the accusump charged up properly so the whole system has the right amount of oil probably takes a bit of trial and error. Worst case I suppose you have a couple extra quarts of oil in the pan, if the valve leaks or you forget to close it.

Fabio, it's a piston running in a teflon-lined bore. According to their site they come in 1, 2, or 3 qt sizes, 2 qt+ recommended for small V8 engines. I imagine that the 3 qt is the more suitable one for 928 engines. As for charge pressure, I can't find their specific recommendations but if you consider that that charge pressure becomes your oil pressure when the accusump is called upon, I would think you'd want at least 2-3 bar when nearly empty of oil, but not too high or your oil pump won't be able to fill it with much oil. Lots of people with direct experience w/accusump rather than theory/anecdotes could give you better specifics.

I wonder if it would make sense to have a vertical tube somewhere in the system that could catch air bubbles and allow you to bleed them off later? The oil may move too fast for something like this to work.

Fastest928

There is a bleeder in the accusump.

FlyingDog

Dry sump has 2+ pumps. One (or more) pulls oil out of the pan and puts it in an unpressurized tank (where hopefully all aeration is removed). The second provides high pressure oil from the tank to the engine. On a 928 you could use the factory pump as the high pressure pump.

The accusump uses just the factory pump and the whole system is pressurized. When supply is inadequate, the pressure of the system drops and the accusump releases oil. It's like a pressure tank in your water system at home.

Somebody mentioned that the accusump should have 2-3bar of pressure when not full. If that was the case, it would drain completely at idle and only fill when pressure is increased at higher rpms when more oil is needed. I think the minimum oil pressure you would see would be about right for the empty accusump (~1bar). Hopefully it will be filled at whatever pressure is necessary for high rpms (~5bar?). The pressure release in a 928 is at 8bar.

SharkSkin

I have seen various parts combinations(in other than Porsche engines so far) that result in interference between the radius on the bearing and the radius on the journal. In extreme cases this can result in a clearance less than or very close to the clearance on the bearing surface itself. Something I have come across in Mopar big-blocks and in Nissan L-series when mixing and matching parts. If it's still not clear what I'm talking about -- the red line is the journal, the black line the bearing. Choices in this case are to find a better matching bearing, or change the radius on either the bearing or the journal.

With the purpose of the thread being to solicit engine building tips, I offered that as one of mine. If you want to look down your nose at the practice, that's fine. Also, I am not a pro engine builder, so it's no skin off my *** to ignore your slight.

The fact is, the practice has been proven to work very well as a final *check* on the assembly. Of course significant effort goes into measuring and characterizing rods, bearings, journals, etc *before* assembly. More than once I have discovered fitment issues at the last minute this way -- a tiny bit of foreign matter, etc. is all it takes to render all of the careful measurement irrelevant.

Bill Ball

Update on the the project. All the lifters were trashed by the bearing debris that got into the oilways and made it to the heads. The head shop said they cannot be cleaned reliably. Dennis will need to buy all new lifters. As far as I can see, this contamination should not have been possible unless there was a defect in the lube system that allowed the oil to bypass the filter.

There are other problems with the heads (worn guides, eroded head surface), but they are in good hands and can be refurb'd to be at least as good as new. With Jim's contacts, we have found excellent local resources.

Dennis and I should finally be picking up a nice low mile S4 shortblock tomorrow and get the crank out, magnafluxed and sent for oil flow drilling at Taylor Engine. If the rest of the shortblock is good we should be ready to build in a week or two.

Vilhuer

Strange if surfaces in heads which get oil feed are not also destroyed. I hope this is the case but it doesn't make sense to me.

Bill Ball

Cams? Cam holders? Well, for some reason the debris was trapped in the lifter galleys and lifters. We didn't see damage elsewhere and the heads looked clean until we removed the lifters which were rather well jammed. Then it was, "Egad!" Even the lifter bores look OK and the shop concurred while recommending not to try to clean the lifters (even though we know how to disassemble them).

SwayBar

Here is the factory manual for the Accusump:

http://www.accusump.com/accusump.pdf/instructions.pdf

...and goto page 5 for how to set it's pre-charge, which is 7 to 10 psi.

The entire manual is required reading for anyone with an Accusump, especially page 2 on how to install it. The little gem in that diagram is the one-way check-valve which will make the unit operate more efficiently by making the discharged oil go directly into the engine versus possibly meandering up into the oil cooler where it's not needed.

Vilhuer

Was thinking about lifter bores and cam holders. Debris in lifters had to go through grooves in lifter bores. Good thing about them is that they can be measured very easily. If they are good that is excellent. Probably needles to mention this but I would take end plug away and clean all oil galleys very thoroughly.

SwayBar

The workshop manuals on page 17 - 11 concurs with the head shop regarding replacement of the lifters.

Fastest928

The one way check valve is crucial ... we use aircraft quality check valves with very low cracking pressure and use -12 hose, rather than the -10 they supply.

The System 1 filter is a 5 micron filter mesh with bypass valve.

I strongly suggest using the stock valve guide material...it is hard and wears very very well.

Marc