I have a disassembled S2 motor and never really looked at the oil pan (duh?).
They will know Karl and Renee (us), we have been instructing for them for years

 

Oh, doh. You are the guys I parked across the road from that cold weekend at VIR! I apologize for my confusion.

 

I'm rebuilding my '86 951.

Adding crank scraper, cross drill (sorry already purchased), baffle, and I added windage ports
between #1 & #2 and #3 & #4. Hoping the complete set will help keep the car on the track.

Mike

 

Harvey, I enjoyed your article. I offer these thoughts. I believe that the fix for #2 rod bearing failure was an evolution thing with some of the enhancements not available to the fixers in the beginning. The cross-drilled crankshaft allows for orifices for the entrained air to escape and not starve the rod bearing for oil.
First, the crankshaft was cross-drilled, the pickup ring was installed to the screen of the pickup tube, and the baffle was installed in the oil pan to handle oil starvation on high G right handers. This prevented the #2 rod bearing failure.
Then engine builders discovere the crankshaft scraper to reduce air entrainment and reduce HP losses, then they discovered that the 951 pan was deeper than the 944 stock pan.
You added all of these enhancements to your oil system except the cross-drilled crankshaft and have had success.
My question, if an engine builder does not have all of the extra enhancement available to him, crank scraper and 951 oil pan, will there be or not be an a #2 rod bearing failure?
Cross-drilling a crankshaft is about $200. What is that cost vs cost of taking the risk of not cross-drilling the crankshaft.
What are your thoughts?
Thanks,Tom

 

Harvey, sounds very likely...yes that was us.
What I said was ," tell them that Karl and Renee said hi.
Oh and hi to you!

 

Oh, my lord Tom, I don't know Why can't we just locate one of the Porsche engineers from the 80's that knows this story?

I have now torn down 3 engines from 85 or earlier. The earlier 2 had cross drilled cranks. The 85 did not. I can't explain that any more than I already have, sorry.

My single best silver bullet that I can offer is to buy the Valvoline (or comparable) Racing oils that say on the label that they are formulated to resist foaming and leave it at that. This is not an altogether inexpensive solution. I am spending $50 per oil change and doing it quite a bit but I just don't see that cross drilling the crank is accomplishing very much. I rest my case on my interstate in Charlotte analogy

 

Forgive me if I'm suggesting something stupid or not possible (I'm an EE, not ME)

I realize that one of the solutions is a dry-sump, which is used to separate the air from oil by letting the oil to "settle" before being "re-used".

However is there a way to separate the air bubbles from the oil in our system?

So the oil is downstream of our oil filter connection, in fact on turbos (and our race car)
there are oil coolers post filter but before heading back to the block and our beloved bearings.

Is there a mechanism that can extract or separate the air and oil post filter?

I.e. I could put it in series with my oil coolers?

just thinking out loud.

thanks,

Mike

 

Nothing pops into my head in the way of an air filter. If you're taking out air, it needs to vent to somewhere. In the dry sump system, the "swirl tank" which removes the air, is on the downstream ambient pressure side. A simple vent out of the top of the tank suffices. But on the filter side the oils under pressure and venting the air is tricky. Not impossible but tricky.

I've only been running 944's for 3 years. I started to hear about #2 bearing failures but I wouldn't say they are common. We have established that the #2 bearing is the weak link and that the cause may be air in the oil. What we can't determine is what those folks that had failures did to push their engine over the edge. Were they running old oil? Were they running less than a racing oil? Wrong weight/viscosity? Worn rings and a lot of blow by that contaminates the oil? Did they miss a shift and over rev their engine? Did they have a dirty radiator and thus a not so cool engine? My point is that it is really hard to do the forensics on this because there are so many variables. But if you set your car up well and do some or most of the things that I suggested in my article that may be sufficient. Fancy hardware fixes not required.

I just finished building a back-up engine. Karma says that now my current engine will last forever

 

Hey Harvey,...couple of points.
My car has so much blow by that I have to open the oil fill cap when doing an intake pressure test or the bubbling through the catch can is so loud that I can't hear for leaks. My crank case and intake are isolated from each other, not counting blow by. I run Moble 1, 15-50, not what I would call race oil. I bought this motor and ran it three years before doing rod bearings and they where not as bad as I have seen.
My previous motor had 86k street miles on it and the rod bearings looked bad but #2 was gone. I do usually shift by 6000rpm.

Like I said just points. P.S. am building a new motor as we "speak".

 

very good writeup, thank you for posting!!

 

I do usually shift by 6000rpm.

Hey Karl, what goes on behind the red haze stays behind the red haze

 

I've lost 3 # 2 rod bearings in 3 years -- on two different cars.

Granted two times I think it was oil pump related. Nonetheless these
are track/race cars and are driven hard.

If you truly believe in the oil bubbles theory -- and a drysump system is prohibitively expensive -- I'm going to dig into the post filter pressurized AOS concept.

M

 

If I may I would like to add that the pump is marginal for racing use.
If we consider the rotational forces in play the rotating crank wants to throw the oil away from its centre, where the feeds to the rod bearings are located. The higher the RPM the higher the pressure needed to overcome the weight of the rotating oil. The oil pump is a compromise to work on cold starts and street use and can't provide high enough pressure at high RPM.

According to my engineering buddy who did some rough calculations the weight of the oil in the crank journal holes equate to rougly 3 bar pressure at high RPM. This would imply that if the pump delivers 4 bar pressure we are only really left with 1 bar to keep the rod bearing from making contact with the crank. (I don't remember the actual numbers but they can be easily calculated).

While I agree with the bubbles theory, and believe we need a revised sump to deal with it, I also believe a better oil pump would help a lot.

 

Takk for oppdateringen...
Hvordan vil ulike olje viscosities påvirke trykket som kreves?


It has been at least 30+ months since these sites were last referenced..

Oil System Breather:
http://www.performance928.com/cgi-bi...ss_parent=1128

Frothy Aeration Slosh:

$4800 Dry Sump Kit:
http://www.lindseyracing.com/LR/Parts/LRDSUMP.html

I post these for relative newcomers like me who'd benefit from their own research on our engine's racing Achilles heal and as a supplement to Harvey's great blog.

Cheers
Mike

 

nice article. thanks