Bill Ball

A stock motor should able to do fine. I'm not convinced the crank drilling is needed. Clearly there are oil supply issues under some condiitons. Drilling MAY help that, but there are other reasonable solutions and precautions to avoid this problem.

Dennis drove his original bone stock motor to over 60 events. It held up fine. However, it failed soon after an elective bearing job. Same with the current motor, although it went South even quicker. Obviously, we do not want the same thing to happen again, although the root cause of these two failures is debatable. There was a tremendous amount of bearing debris throughout the lubrication system. I mean gobs and gobs of copper everywhere [note: it's even in the lifters and filling the lifter oil galleys.] Only 2-6 were trashed. The rest of the bearings were just surface scored. The engineers can discuss the crank bending. I don't know if the heat from the rod bearings is enough to explain it, but probably so. 2-6 were charcoal black and blue, including the crank casting near 2-6.

RyanPerrella

What kind of rod bearings were used, and how many track events did he do before this happened?

john gill

I may have missed this earlier, but as Mr Kiborts Engine was the Holbert car , (Mark to correct) wouldnt it be more informative to strip that engine down to see what was done from the factory as I believe this car has seen a long life on the track , I believe that the improvements that have been made this engine would be beneficial to all , I am sure that all would be willing to throw & help Mark in this regard

my 10 cents worth
JG

GregBBRD

I'm betting that the rod bearings used were not factory. As I said, the cheaper rod bearings that everyone tends to use are the secondard market Glycos. They are very tight and do not provide enough bearing clearance. The factory assembled these engines with 3 different size rods bearings, according to what size the crank was. Porsche no longer offers all three sizes, but they do provide them in the boxes of rod bearings that they sell. You just need to buy a whole bunch to get the right sizes....and they are expensive....but so is a blown up engine.

gb


gb

lorenolson888

Hi Greg,

this is good info... what would be the standard tolerance and clearance...

Should Dennis and billstart by buying a couple of boxes and see if they get lucky...

or would it be best to just mic the crank rods and journals and just have them made (if possible)...

Loren

IcemanG17

Another good idea is find out what tolerance group is needed.....them buy'em from Greg...since he prolly has a bunch around!

lorenolson888

Hmm... yes that is a good idea....

LO

Bill Ball

The bearings had a mark that looked like this to my eyes:

mark kibort

Once i get the engine out for replacement with the stoker, we will have some answers.

as far as bearing changes,(on scot's and my 5 liter part euro ) ive use Glycol. (i think) arent they in the red box?
anyway, do check the clearances. using plastigauge, all tollerances were per the WSMs. (a little on the loose side of the tollerance.)

MK

Louie928

Bill,
I sent Kevin drawings for my crank scrapers and sump cover. He has much experience with this stuff and modified it to be how he thought best. Some of Kevin's ideas ended up in what I have now although Kevin's hardware looks quite different from mine. My initial crank scraper and sump cover/windage tray ideas came from Mike Schmidt and Smokey Yunik.

You sound serious about keeping Dennis' motor alive. I sort of have the same old mantra regarding 928 oil control. Keep the crank from hitting the oil. The proximity of the crank to the oil in the sump is way too close. Add a high G, high RPM left corner, and you'll have a problem. The stock lower end breather system is really bad. Do whatever you can to increase the breathing capacity of the lower end so blow by doesn't blow oil up the oil drain passages and out the cam breathers. The easiest way is to put a breather line on the filler cap. The bigger the better. Have it project down into the cap so oil on the surface can't get out the breater so easily. I put a 3/8" aluminum spacer between the block and the oil sump to get the oil further away from the crank. No sump gasket. It's not much, but every bit helps. It helps to stiffen the block too. The stock starter won't fit anymore. A windage tray inside should help also. I have one made from heavy screen made for the purpose. I've had very good results on my 6.5 motor so far, but no amount of street driving or dyno time is as good as one lap around Thunderhill to gauge success in oil control. I've not done that yet with this engine. Only with the original engine that lost #2 rod bearing shortly after a stint at TH. Accusump is great. I have my electric valve operated one connected to my fuel pump so it is activated with the pump. I can see the oil pressure come up to about 2.5 bar as soon as I turn on the ignition before I start the engine. My ECU turns on the pump for 2 or 3 seconds when the ignition is switched on. Do not over fill the sump. I think everyone agrees that a dry sump is best. That's about all I can offer.

IcemanG17

Okay here is a newbie ???? an accusump is NOT a dry sump......whats the difference? Doe accusump just increase the capacity and add a second pump?

Is there a true dry sump system out there...I know Marc T was working on one & Mark A has one (??) in his race car? So to clarify my clouded mind....a dry sump is a flat oil pan that is very close to the crank...& all the oil is kept separate from the bottom of the engine and pumped back in by (typically) a couple pumps? Does this sound right?

Bill Ball

Louis:

Thanks for the extra input. I spent some time reviewing the material you have on your site and appreciate your willingness to share your experiences and findings.

SharkSkin

I'm talking about verifying that the clearances are what you think they are when the assembly is torqued together, using plastigage. Surely you've heard of this before???

You can mic everything in sight, calculate clearances, etc. and STILL end up with a different clearance than you expected when the bearing is assembled, because things take on a different shape when torqued. BTDT.

Surely a discussion of QC methods/risks, variances in finished part sizes, issues with mis-boxed parts, etc is not necessary with this crowd?

Also I think that going straight to the track on new bearings is a bad idea, unless the crank has been polished(even then I would want to run it in for a while longer than the trip to the track, but I tend to be extra-careful about such things). Hopefully most here understand how a new bearing on a used crank will have a very small contact area until the high spots on the crank wear into the bearings.

SharkSkin

Brian, that's close enough -- a dry sump, instead of storing oil in the pan, stores it elsewhere, in a tank of some sort. Oil is scavenged from the sump and pumped to a storage tank, from there it exits at or near the bottom of the tank to supply oil to the suction side of the main oil pump.

A dry sump may or may not be very close to the crank -- ideally it's not so close that oil splashes off of it back onto the crank.

SharkSkin

Found some simple GIFs of accusump operation on their site, Brian:

Normal operation, oil pump pressurizes accusump:



Oil pump not providing enough oil -- accusump provides pressure(there is a check valve between the accusump and oil pump, not shown in this diagram):



I think it's worth noting that if the oil pump is pumping air into the lines, I don't see how that air can get out -- unless someone can enlighten me on this point, I believe you can still get a slug of air at the bearings once the oil pump takes over again. A dry sump system should never allow the oil pump to suck air, eliminating this situation.