Pilot bearing engagment issue for Porsche boxes

Hey guys,

I'm running into an issue with the input shaft to pilot bearing engagement depth. I'm using the G96.50 which is identical (AFAIK) to all G50 variants in the bell housing/clutch interface measurements. So I'm sure many others have dealt with what I'm noticing here.

The issue is I'm only getting 0.196" of engagement. The tip of the trans input shaft is beveled of course so when subtracting the bevel section (0.078") I'm left with 0.118" of actual contact between pilot bearing and input shaft. I don't feel comfortable with that number. What have others done to remedy this? At this point I'm thinking of shimming the back of the pilot bearing by about 1/4" to move pilot/adapter forward.

Below is my math for arriving at the above figure if anybody cares to double check it.

Trans input shaft protrusion beyond bellhousing face = 0.278"
Input shaft bevel = 0.078"
RCR adapter face (main) to bottom of crank (pilot receiver) = 0.696"
*above does not include radius cut inside crank and basically measures as far back as the pilot/adapter will seat itself
RCR adapter extrusion depth (trans mounting surface) = 0.093"
RCR adapter extrusion face to bottom of crank = 0.603"
Kennedy pilot/adapter thickness = 0.521"
RCR Adapter trans mounting face to start of pilot = 0.082"
Input shaft engagement = 0.196"
Input shaft engagement minus bevel = 0.118"

I calculated engagement as:
Trans input shaft protrusion minus RCR Adapter trans mounting face to start of pilot

Howard Jones

I have a G50-01 and a old school small block Chevy.

I think I recall my pilot shaft went completely into the pilot bearing and about a 1/8 beyond. I don't think 2 tens is right and will lead to early bearing failure at least. I can't remember if the bearing housing is completely buried in the crank or if it ends up proud somewhat, but I do recall that the piglet shaft splines cleared the pilot bearing rearmost race by about 1/8 to 1/4".

If you install the bearing adapter in the crank, then install the gearbox without the flywheel and clutch, you can see pilot shaft to input shaft fit as I did by looking through the holes in the gearbox with a flash light. Be aware that if the bearing adapter goes in tight they can be difficult to get back out. There is a good way to do this with a bolt and grease and then hydraulic it out. More on this if it becomes necessary.

If I couldn't figure it out I would call Kennedy and ask them the dimensions of the correct pilot adapter housing and compare to yours'. It might be the wrong one. If t is I think they would send you a new one without much fuss.

Terry Oxandale

Skinny Man
I agree with Howard. My adapter sticks out about .250" from the end of the crank (LS2), but I think my was about .600" thick or thicker. Perhaps KEP has different thickness of adapters for the LS series.

Fran Hall RCR

GT40s Sponsor
If Kennedy has changed or has a new plate thickness I have no problem shaving some off our plate Mark...just send it back with the new dimension and we can sort it for you asap.

Its not something we have ever had to do in the past though...but here to help if you need us.
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Thanks for the responses guys! I just spoke to Kennedy and it looks like I've been sent the wrong part. They sent me the old school SBC adapter which has the same OD as the LS versions so it's easy to confuse, luckily I didn't just install it.

The LS version measures 0.650" so about 0.130" thicker than their previous adapter and it's got a solid bearing as opposed to the older one that uses an exposed needle bearing, KEP identifies it as part 1760-90+. By my calculation the correct pilot will gives me 0.325" of insertion which is much better. I think I might still use an 1/8" shim to get the tapered part of input shaft past the bearing to optimize contact.

Thanks for the offer Fran, I don't think that will be necessary.
We had the same problem, which led to pilot bearing failure, and Input shaft damage. $$$


I don't think there is enough meat on the adapter plate to machine it without weakening the threads for the trans mounting studs.

Here is our solution:


Going to a high quality sealed roller bearing is more durable than the little needle bearing, and spacing it out towards the transaxle fixes the engagement issue. Also we are machining the flywheel where the ring gear mounts, as the starter doesn't fully engage the ring gear also (not done yet in this photo) to move the ring gear closer also.
Thanks for sharing your experience Ted, always appreciated. If you were using the pilot with the exposed needle bearings then you had the old (or incorrect) version as well, there was a redesign prompted by a customer pointing out the issue. KEP's new design looks quite similar to your custom piece and uses a sealed bearing.

Some nitty gritty details follow in case somebody might find it useful for their build. I just received the correct pilot and took more measurements. The new bearing is 0.652" thick as expected and has an effective bearing surface of 0.350" that starts from the front edge of the adapter. Following my previous measurements detailed in the first post this pilot nets 0.249" of contact with the input shaft after subtracting the 0.078" bevel at the tip of input shaft. So 1/4" sounds pretty reasonable to me considering I measured the OEM wear pattern to be 0.275". However by adding a shim of 0.100" to 0.120" the number improves to 0.350" or basically the max possible meaning the non beveled part of the shaft is making complete contact with the 0.350" wide bearing.

By the way I verified my measurements by taking a clay impression of the input shaft against the crankshaft cavity with the trans installed. Those measurements were within 0.012" so I'm pretty confident that the numbers are right.

Here are some measurements I took to establish ring gear to starter relationship. I'm using the SPEC aluminum flywheel but as far as I know it's exact in critical dimensions to KEPs.

RCR Adapter extrusion face to starter teeth = 0.987"
Starter teeth bevel section = 0.058"
RCR Adapter extrusion face to ring gear start = 0.924"
Ring gear tooth width = 0.354"

Subtracting where the ring gear starts from where the starter teeth start I get 0.063" of non contacting part of the teeth. That translates to 0.291" or 82% contact between starter/ring gear. I'm guessing that must be adequate given that we haven't heard any reports of people having issues. However :) machining 0.121" off the back of the flywheel where the ring gear sits as Ted suggests would completely engage the ring gear and also move the contact point further down the starter teeth where there is more strength. The 0.121" figure is basically starter teeth bevel section + non contacting part of ring gear.


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