Intermediate shaft gears
 

We are going ahead with building a 3.0 litre SC based engine which we hope to rev to around 8200 rpm.

I have seen many of the posts concerning oiling mods which I can understand and agree with and we will corss-drill etc, etc.

I see that some companies offer staight cut intermediate gears, either steel or aluminium and I wonder if I should be using steel gears or if the standard gears are good enough?

Any thought welcome.

Regards

Chris

gears
 

Chris, we offer a straight cut gear set for the 911 engine that we are currently out of stock, I would as an alternative use the steel set from a 964 (you will need both the crank gear and the intermediate shaft), they can be found used reasonable, the alum. gears work fine on the street, but higher valve spring pressures and high RPM along with big scavenge oil pumps the wear is increased alot.
Mike Bruns JBRacing.com

I'd concur with Mike; the 964 gearsets are very durable and an excellent choice for anything but an all-out race engine.

Straight-cut gears are very noisy.

When the teeth on my aluminum IS gear stripped, and all 12 rockers broke at once, I became a fan of steel gears. I got straight cut ones, figuring they put less end load on the crank and IS bearings, and are more efficient.

In a race motor I never have noticed extra noise from the straight cut.

The strait cut ones I have seen advertised are way over priced, seems to me. But demand is small.

I hadn't thought about a steel helical (or whatever it is) gear for the IS shaft. Will the 964 gear work with the earlier engines? Work with the earlier crank gear, or must these be a set?

Walt

gears
 

Walt, the 964 gears are a matched set (also the tooth count is different) and they will work fine on the earlier cranks, I have not tried them on the alum. 2.0 cases yet.
Mike Bruns JBRacing.com

Mike

Er - is the ratio the same despite a different tooth count? So a guy could use his older style IS and cam gears?

Memory (a thin reed at times) tells me that while the alum 2.0 case IS shafts are different (that I am sure of), the aluminum crank gear part is the same (or easily adapted). The IS chain wheels are the same. Which should mean that this 964 all steel gear set should work in all 911/930 cases.

Walt

gears
 

the 964 has a tooth count of 35/60 and the earlier style has 28/48 the ratio is the same, the early 2.0 IS has 3 bolts and 3 dowl pins to secure it, we drill and tap the IS to make it 6 bolts when we do the straight cut gears, to be sure on the 964 stuff it just needs to be mocked up to confirm, I will do that soon.
Mike Bruns

In a conversation w/ Steve Weiner, he told me the 964 I shaft works in all cases.

Kenik:
The aluminum 2.0 layshafts have the outer bearing larger in diameter than the mag case shafts. The 2.0 Al is also shorter, but that is after the bearing to the outside of the case. I've got both sitting on my workbench.

Does anyone make a thick bearing to use the 'common' mag is in a Al case (with a trim on the thrust face)?

There must have been more to it then and forgot the details. My guess is that you simply weld up the saddle and rebore the i-shaft carrier. Easy and done.

As far as the length, I think this is why you have to be so careful with the end play on the early shaft. Perhaps the later design's length is part of the reason it is easier on the non sand-cast cases?

The end plate for the early sand cast intermediate shaft serves as a thrust bearing, which is why it has an adjustment spec. This seems to work fine. Oil in that area is under some pressure, which seems to prevent metal to metal rubbing. Which is why I can get away with using the later magnesium end plates instead of the cast iron original.

This also works with the straight cut gears I have on this engine, which aren't going to be generating much axial thrust.

Walt

IS research...