early aluminum case intermediate shaft question

gestalt1 · 02-16-2010, 11:09 AM

hi, i have a nice sandcast early case but no matching intermediate shaft. i do have a later style shaft from a 2.7 engine. is it more costly to machine the case for the bearings or to track down the early shaft? is there and advantage to having the shaft on the bearings vs the bare aluminum case?

thanks!

Flat6pac · 02-16-2010, 12:52 PM

The 2 shafts are different sizes, considerably different..
Bruce

gestalt1 · 02-16-2010, 01:10 PM

yes they are different but the case can be modified to use the later style bearings and allow the use of the later shaft. i just don't know if the machining is more expensive than hunting down an early shaft.

tadd · 02-16-2010, 01:43 PM

The outboard bearing (the one closest to the thrust surface) is MUCH larger on the early shaft than the later mag case shaft. I would assume welding and sizing would be required even with the thickness of the bearing. The length difference is not a real issue given that the extra is after the bearing journal.

I have both at home and I can measure if you like.

t

gestalt1 · 02-16-2010, 01:52 PM

don't bother, sounds like finding the correct shaft would be the way to go.

Walt Fricke · 02-16-2010, 06:06 PM

The correct shaft is doubtless the easiest way to go in the short run. I have never had an issue in my sand cast race motor cases with the fact that there is no babbit bearing at either end. And instead of a thrust bearing, you do some measuring and use shims on the cover plate to set end play.

However, there are some disadvantages. I worked a deal and got some straight cut steel IS to crank gears. These were dimensioned from the later shaft, and I had to do some fiddling to use with the early shaft, and the mesh is a little offset. If you are thinking about anything other than a stock early aluminum IS gear and crank gear, you might consider this.

In addition, I think early IS shafts are getting hard to find (like the cases).

I have heard of, though not seen, a way of reducing the larger bearing hole in the case to fit a later shaft. Must involve machining something, maybe doing some drilling and tapping to hold it in place. Don't know who does this, but it would be simpler and less stressful than a weld-up and bore job, I would suppose.

Haven't done this on my engines, though. Getting along with the old IS.

gestalt1 · 02-16-2010, 06:26 PM

since the cams themselves ride on the bare aluminum of the cam towers i guess there would be no problem for the intermediate shaft to do the same. do the strait-cut gears make a dramatic difference other than costing a lot and making noise?

tadd · 02-16-2010, 06:54 PM

Most folks just want to use steel gears. Turning a big pump and cams the aluminum ones are known to strip teeth. The 964 are steel and helical. They also have a different tooth count and thus require a different matching crank gear. I've been told they are a bolt up but I have not got far enough to verify.

MBruns · 02-17-2010, 05:07 AM

Ollies is tooled up to weld and machine the case to use the late style shaft setup, if you are doing other machine/prep work it would be a good idea and its not that expensive. It will allow you to run the 964 steel gears or other straight cut gears, for a hi RPM engine the alum. gears don't hold up well.

Mike Bruns JBRacing.com

stownsen914 · 02-17-2010, 06:53 AM

I had Competition Engineering modify one of the early sand cast aluminum 911 cases to use the later layshaft with bearings. I believe he welded an insert into the case to reduce the diameter to match that of the later shaft, and then machined it to fit. I had this done years ago, and 50+ engine hours later it working well.

Scott

Cupcar · Cupcar's Garage

Ollies does a good job welding up and re-machining the case for the late shaft.

The early shafts are almost impossible to find in good condition and the late steel geared 993 shaft is a better design shaft anyway.

Walt Fricke · 02-17-2010, 10:46 AM

Mating any steel gear to the early IS shaft should be approached cautiously. The gear will sit in a different position longitudinally relative to the crank gear. In my case, I reversed the crank gear (the hub protruded a bit on one side) to get an acceptable percentage of mesh (only a little bit of gear not meshing), but had I know of this issue I'd have had somethng machined - wouldn't have been difficult.

Of course, if you have early Porsche factory racing steel gears sitting in your parts box, you are good to go. Ha.

I didn't know the 993 shaft was a better mousetrap. Steel gears certainly are better for modified race motors - when my aluminum gear stripped, all 12 rocker arms broke. Ruined my race and weekend at Hallett. On the other hand, I see no reason to use steel in my stock class 3.0 SC motor - not spinning that fast, cam is mild, pump is stock.

For a race motor I like straight cut gears. Of course, if I am wrong in my assumption that they have less friction (parasitic drag?) than helical gears, why bother. But noise is not an issue in a race motor. On the other hand, the straight cut gears on the market cost a whale of a lot more than using the later factory stock steel helicals.

Were I more venturesome I'd even try a VW hotrod trick: mill a groove circumferentially around the IS gear so trapped oil can escape more easily.

Cupcar · Cupcar's Garage

Below is early case with 993 shaft, case mods by Ollies...

Peterfrans · 02-17-2010, 12:37 PM

will the 964/993/996turbo shaft mate with a standard crank or are the gears paired to each other and is my 996turbo intermediate shaft worthless without the original gear on the crank?

MBruns · 05:40 AM

They are a matched set with an engraved set # like trans. gears, the tooth count is different but the ratio is the same. Peter without the crank gear its not worthless but you would have to check the setup and backlash to be sure, plus find another set that is missing its mate, alot of trans gears are matched to be sure they run quiet together as well as proper backlash.

Mike Bruns JBRacing.com

kenikh · 02-18-2010, 08:19 AM

Tell me about the pain of finding the right gear. Ihave a 964 i-shaft and no gear. You can't buy a gear separately and finding one used is, well, painful. Then you have the crapshoot that they are going to mate within spec, sight unseen.

Peterfrans · 02-18-2010, 09:52 AM

Quote:

Originally Posted by kenikh

Tell me about the pain of finding the right gear. Ihave a 964 i-shaft and no gear. You can't buy a gear separately and finding one used is, well, painful. Then you have the crapshoot that they are going to mate within spec, sight unseen.

I have exactly the same problem, a nice 996 shaft and no gear. The guy I bought the oilpump and intermediate shaft from still has the crank with gear but seems to be unable or unwilling to pull it off and sell it to me.

gestalt1 · 02-19-2010, 05:44 AM

wow, great info here - thanks! not sure what i'm gong to do, i have seen early shafts sell for about $350, the later style go for about $50. if the machining cost is around $300 it would be worth it. still not sure what to do about the gears however.

Peterfrans · 02-19-2010, 06:00 AM

I have an early shaft that came with my case, but was deemed out of spec by ollies (I am happy to send you that one) so it is a bit of a gamble buying these for serious money.