drnick

alex, i will go with john venniger on the fate of the UK race mob runnning scrapers - the jury is out and the verdict is not in.. . yet!

Jim bailey - 928 International

The very first mention of "944 disease" that I saw was a paper by John Kim Crumb nearly 20 years ago. As the Porsche Club of America 928 technical editor he had become aware that the 928 ALSO suffered from rod bearing issues when tracked hard on sticky tires. Typically 10-12 hrs was enough time. Mr Crumb personally had 2-6 bearing failures twice on his GT as I recall. His "Project 928" 4.7 Euro at the first track event for the new owner it nearly cut the engine in half with a catastrophic 2-6 failure and broken rod.

hacker-pschorr

Has anyone mentioned or has it been discussed to open up the side clearance of the connecting rods to improve lubrication over the rod bearings?

Vilhuer

Rod big end holes were machined while rod was bolted together. Hole is not exactly centered compared to rod bolt holes. If one mixes lower ends between rods bearing halfs will not result round hole even when lower ends are installed correct way around. That is simple reason for 928 rod numbering. AFAIK numbering system was in use several years before 944 even existed.

These really are't that high precision parts. Piston weight tolerance +/-4 grams is one sign of it. Only truly accurate tolerances are between cylinder wall and piston plus some critical bearing surfaces. There are several differences in similar rod raw castings that are on quick look exact same. This will probably result few g weight difference but Porsche only saw the need to get their weight to close enough. Anything closer would have meant much more machining needed to make weight accurate to within +/-1 g for example. They did get actual component weights which went into one engine at the factory very close to same by selecting same weight parts to one single engine. But this doesn't prevent anyone from mounting indivisual parts from for example any S4 engine into another S4 engine without checking their weights. This is ok from Porsches point of view since all parts were done to enough tight tolerances. How they look can vary quite a bit but they are all intechangeable within each engine style unless factory documentation says othervise. Exceptions are usually listed in yearly changes documents more often than WSM or PET even.

Stroke is same 78.9mm on all '78-91 cranks. There are two separate differences in cranks for sure and possible third one.

1. Since thrust bearing side height was made larger it was also needed to make crank side where those bearing sides lean on taller. Othervise bearing side height increase would have been useless. This means old crank can work with new bearing and other way around. Only thing needing some attention is engine block itself. Early block needs to be modified a little for it to accept later tall sided bearing. No big deal at all to do in any home garage with correct tools.

2. Crank oil hole diameter was increased from 4mm to 5mm some time in early eighties. This do not have anything to do directly with any other changes and thus either small or large holed crank will work with any bearing version.

3. Due to possible piston and/or rod weight changes its possible cranks meant for different engine types can have different size counterweights. I haven't checked part numbers to see if this is true or not. PET should have all the info we need to determine this since times when changes #1 and #2 occured are known.

Can't remember seeing it and there might be good reason for it. Rod bearings are force fed by oil pump throught crank holes and oil drains out from rod bearing sides. If sides are made more open this will lower oil pressure in bearing surface. At least thats my thinking why it would be bad thing to cut oil feeds into rod sides.

Bill Ball

But you can see Jay does some cross-drilling as well. Hold-on, and I'll try to make the differences clear and possibly what they imply in terms of oiling. Jay went over this but I don't remember the details, so I'll have to consult people who understand this better than me.

FlyingDog

If the pressure is reduced, the velocity will increase. Could the risk from the reduction in pressure be offset by the ability to clear aerated oil faster?

hacker-pschorr

This is something Todd talks about quite a bit. He's had some experience (non 928) with engines tossing rod bearings. This has worked with other engines he's worked with or has a lot of knowledge on.
That's part of the idea

Vilhuer

Is other part to allow oil go into bearings through same holes against its normal flow direction?

There so many relatively simple ideas which can be done to all stock engines by anyone rebuilding them that its hard to keep track of them all. It could pay of though and result as good engine as possible this side of drysump.

Fabio421

This may be a really bad idea but maybe it has some merit. This only addresses the part of the problem that people are trying to remedy by drysumping or using an accusump.

Why does the oil pick up tube have to be stationary? Why couldn't you machine a swivel for the oil pickup that allows it to swival from one side to the other under cornering? The oil is thrown from left to right, why not allow the pick up to do the same. This style of pick up is used in a string trimmer (weed wacker) for the fuel pick up. This is why you can turn a trimmer up on end to use it as an edger and it doesn't starve for fuel.
This swival could be made to have a limited travel so it doesn't bang against the sides of the pan and it could even be lightly spring loaded so that it self centers when not under a cornering load.

OK fire away. Why wont it work?

[flame suit on]

FlyingDog

To make a good seal, you will have friction in your pivot. If your pivot fails and the pickup is on the wrong side, it would be worse than having it centered all the time.

Fabio421

Yes and no. The PSI at the inlet to the pump is very minimal so the amount of friction required to seal it would be minimal as well. Having it lightly sprung in both directions would lessen any chance that it would stick. If for some reason it was stuck to one side it would only be a bad thing when turning hard in one direction.

But you do bring up a great point that I didn't think of before.

Mike Simard

If you can find Erkka's pictures of his Moldex with rods in the passages that will help explain the misunderstood "drilled like a Chevy" term. The key is that the passages go as shallow as possible under the main surface and straight to the rods, one passage for each rod. You can see that from an end view.
The only way to get a crank drilled like that is to get a Moldex or similar. I dare say it might even be money well spent to have them make a stock stroke crank if you're not interested in a stroker, just to get that oiling.

Vilhuer

Its on message #21 in other thread.

https://rennlist.com/forums/928-forum/380742-how-to-drill-a-5l-crank-like-a-chevy.html

And in here now too.



There are just 8 individual holes. Each hole goes directly from nearest main bearing surface to each rod bearing surface. Making more holes to stock crank might achieve same result. It all depends on what actual problem which causes 2/6 deaths is.

Bill Ball

Compare Erkka's shot, showing the holes going all the way through, to Jay's extra blocked off connections and extra cross-drilling of 3 of the mains in the link to Dennis's illustrations I included earlier. It's all in that one thread on "drilled like a Chevy", but the direct compare and contrast has not been stated there yet.

6.0-928S

Every Race Hemi I've ever had uses a swinging oil pickup. (as well as every one I've ever seen at the strip) They work great. Hemis spin up to 9000 rpm with swinging pickups. There is no friction issue & the pickup follows the oil so as long as the pan is baffled the pickup is always in the oil. I've thought about putting one in my 928 but I'm still tied up with my ITB setup so I put the pickup on the back burner. But it will work.
Hammer