Stan.Shaw@Excell.Net

I put a drilled crank in my 5L hyrbid motor last year, and it only lasted about an hour..... These pictures show it in it's current state..

Some questions;
1. The local machine shop said the journal could be welded up, and would be fine afterwards. Anyone seen any problems with this type of repair/

2. The local machine shop said the crank is slightly bent, but could be straightened. The are not advocates of doing so for a motor used in a track/race car, but they are also accustomed to replacing cranks for much less than Porsche prices. Anyone with good experience having a crank straightened?

3. Anyone have a drilled "like a chevy" (not stroker) crank laying around they don't want?

4. One knowledgeable person looked at this crank and said it was not drilled "like a chevy" properly. Anyone else think the same or differently?

Vilhuer

Hard to say from pictures how it was drilled. Does each conrod oil feed have it's own path that is not connected to any other paths or are some still joined together?

BC

Who drilled the crank first?

Taylor engines in whittier said bent cranks rarely stay "fixed" was the way he said it as I recall.

Stan.Shaw@Excell.Net

Hi Erkka,

Not sure on how the drilling paths work on this.

Hi Brenda,

I bought it drilled, so am not sure what machine shop actually did the drilling.

mark kibort

I have a real nice 4.7 crank with the larger oiling holes if you need one for cheap.
mk

FBIII

If you have the crank welded they would have to straighten it. With all the heat applied during welding straightening it is part of the procedure. I had a forged chevy crank welded years ago and it worked fine. The only flaw in the process was they hadn't checked side clearance on the journal and I was a little over spec after assembly. I guess I should have told them the thickness of two rods before they got started.

Stan.Shaw@Excell.Net

Hi Marck,

I have a spare 5L crank, but it isn't drilled. I don't think you can use a 4.7L crank in a 5L block anyways.


Thanks FBIII, they told me they would straighten it cold and it was not a pretty process....

BC

Different main bearings. 944 mains until 5.0L engines (I think)

jeff jackson

Why would you "want" another crank "drilled like a Chevy" ... when this one "didn't last an hour" ????? What caused this one, to fail so prematurely......looks to me, like it "spun a rod" . Why would you not suspect that the drilling of the oiling passages,, ( and fitting of rods, built for Chevy journals)..., as a root cause of the failure, and want a new one ? You said the shop said the crank was bent...probably by the rod that spun the bearing ??? Welding the journals and straightening and rebalancing a damaged crankshaft for racing, is a dubious proposition, I think...unless the cost of a suitable replacement is "prohibitive"...

atb

Hi Stan,

Was the crank straight and true before you ran it? I would think that would more likely be the culprit of the spun bearing than the cross drilling.

My local machinest that has been doing the work for my stroker motor said that before I lay the crank to bring it in to make sure it's straight. When I stated that it's a billet crank from Scat, he said it doesn't make a difference, he's seen billet Scat SBC cranks that weren't straight that he pulled of the box.

I'm a little puzzled at where the crank was drilled. It looks like they drilled #5 in the top pic and #6 in the bottom pic. Are these the only two rod journals that were drilled? Was any other work done to the crank?

mark kibort

I sure would like to know why the holbert car is staying together with no signs of wear! Amzoil 20-50, kept full, no drop in oil pressure, even around the carocel at Sears or Road america, at 5500rpm. shifted this entire 4th season at 6300 or so instead of the 6000 i normally shift at.

I guess we will never know if porsche did something different to the holbert bottom end to protect it. However, had a bunch of multi year luck with the 4.7 part euro and the 85 5 liter bottom end racer too!
MK

jeff jackson

Who would machine/build a "race engine"...with a crank that wasn't "straight and true" ??? Thats asking,... for this result in my opinion....No credible machine shop or machinist.... would suggest you build a racing motor with a crank that could not be balanced, or wasn't straight. And no one that turned it, to the Chevy rod journal diameter, fitted Chevy rods to it, and drilled it up for Chevy oiling, woudn't have checked these things first. You need to trace this back to the original blueprinting of this engine, and look for answers, I think.
Wait a minute...are you saying, that all he did was "Cross Drill" this crankshaft, atb ???...Cause, I was under the impression when he said the crankshaft was "Drilled like a Chevy"...and in my perspective, that meant, the crankshafts oiling passages, had been redrilled, nd made to match that of tha Chevy smallblock 302 engine, and the main and rod bearing journals of the Porsche crank, were machined to the small block Chevy journal diameter, allowing/mandating the use of popularly availbe Chevy rod and bearing combinations, of almost unlimited configurations, much more reasonably, than custom built "porsche parts".

BC

I think oils aint oils, but there are different issues involved that are pretty clear once we understand how the car was built. I don't have those answers, but small changes add up to big once.

Scraper, crank drill, better oil, better oil cooling, maybe a accusump or dry sump. Maybe even bearing coatings, which I was warned against by one machinist.

FlyingDog

Jeff, Porsche cranks are crossdrilled, but apparently the Chevy way of crossdrilling is better. The only thing done to this crank (so far as I understand it) is that it was cross drilled in the same way as Chevy cranks. There is a thread on Rennlist that details the differences with drawings and a real crank with drillbits to show the passages.

Prionace Glauca

Stan,
I lifted these pictures from Rennlist a little bit ago.
Hope this helps visualize the cross drilling.

FYI: Taylor did mine, no issues to date.