SBC Long Pilot Bearing (1 Viewer)

Joined
Dec 13, 2012
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KY
So my question is, has anyone used one of these in the SBC conversion for any reason and can you state why?

Here is why I ask. I'm nearing completion of my NV4500 install, or should I say I'm about ready to start installing the parts that have been acquired with necessary modifications/adapters. While researching my internal hydraulic slave I ran across something interesting, at least to me. When I pulled the old 3 speed I noticed that there was about 1/4" of the input shaft that was not supported by the pilot bearing (again SBC).

So this got me to thinking. The 3 speed input is 1/2" longer than a Chevy input hence the need for a 1/2" spacer plate between the bellhousing and the trans. So if this is the case and I'm using a factory bellhousing and Chevy input shaft (NV4500) won't I have the same 1/4" of non-supported shaft tip. So I got to playing and came up with this drawing:

Long Pilot Bearing.jpg


I know it may be a little hard to follow but this is what I found. The input shaft has 0.311" clearance with the inside pocket of the crank. So, what does this mean? There is a pilot bearing made for builds where a motor plate is used between the block and bellhousing. These plates are usually 1/4" thick and used for mounting the engine. The long pilot bearing is 1/4" longer than the factory 3/4" bearing and is represented in the drawing with the angled lines. According to my measurements that would still leave 0.061" of clearance between the end of the pilot bearing and the input shaft. I don't have the numbers but I don't believe that if you total the crank end play and the input shaft end play that it would come anywhere near the 0.061".

I've ordered a bearing to see for myself but wondering if anyone else has done this before me.

I forgot to mention, the reason I going here is because I figure the extra 1/4" of support, or wear surface if that's the way you want to look at it, could extend the life of the bearing or at least reduce the amount of wear until it is time for a new clutch. My old pilot bearing had opened to 0.630" - 0.659", slight oval.
 
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Joined
May 9, 2004
Messages
400
Location
Santa Clara, CA
I used the longer one for an SBC to NV4500 (`94 GM version) with an AA bell housing. I believe AA made two bell housings with the earlier one being somewhere around a 1/4" longer.hence requiring the longer pilot. It's been a few years back and I got it from them. It was a solid brass (not sintered /bronze) bushing and probably could have been machined for clearance if needed. I see their website lists an extended bearing PN 716154. Seems like you're on the right track. [Edit: the extended one might be PN 712576]
 
Joined
Dec 13, 2012
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Location
KY
Well I installed the bearing this morning.

DSC00583.JPG


DSC00586.JPG


I then installed the flywheel and checked the bellhousing index. Looks like I don't need to use off-set pins.

Bellhousing Index Numbers.jpg


Flywheel bolts are temporary as I have ARP bolts on the way then the clutch and trans get mounted.
 
Joined
Dec 13, 2012
Messages
1,201
Location
KY
So, I was able to get the trans and transfer case test fit today. I put some clay (Play-Doh) on the input shaft and will double check the clearance when I take things apart.

All the Major Pieces In.jpg
 

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