Crankshaft Pilot Bushing Bore

[Joe C.]

Were all pilot bushing bores machined in the same way, or was a final honing process done on those units intended to be installed in engines destined to be mated to a manual trans?

The reason I ask is that I have a spare 680 crank whose pilot bushing bore diameter measures 1.090". It has a mark on its rear flange that suggests it was originally installed in a car with auto transmission.

I'm not familiar with the engine production process, but my first inclination would be to believe that since all 1962-1965 327 engines received the 680 crank, that there would be no need for designating a specific crank to a specific engine.

[John H.]

Re: Crankshaft Pilot Bushing Bore

Were all pilot bushing bores machined in the same way, or was a final honing process done on those units intended to be installed in engines destined to be mated to a manual trans?

The reason I ask is that I have a spare 680 crank whose pilot bushing bore diameter measures 1.090". It has a mark on its rear flange that suggests it was originally installed in a car with auto transmission.

I'm not familiar with the engine production process, but my first inclination would be to believe that since all 1962-1965 327 engines received the 680 crank, that there would be no need for designating a specific crank to a specific engine.

Joe -

As far as I know, the only SB crankshaft that was specific to a transmission was the 283 crank used with Turboglide, which had a large recess to accommodate the large TG converter pilot; all 327 small-journal cranks were machined for the pilot bushings.

That's a really strange-looking flange configuration - I've never seen one like that before on a 680 crank.

[Domenic T.]

Re: Crankshaft Pilot Bushing Bore

Joe,
This won't answer your question but in the late 50's and later I would visit the bone yard and pick up small blocks to rebuild. I never had a problem putting in the bushing when the crank didn't come with one.
I weighed all the pistons & rods so I could mix & match to the crank. They all weighed the same, flat top, dished, and dome, the rods were all the same weight also and that told me all the cranks were made the same way and had the same balance. That was a smart production move as any thing worked with any combination.
SO I would think they would do the same with the hole so they could use the crank where ever they wanted.
I got my steel BB cranks out of wrecked trucks and the block said "high perf pass". I ordered a piston from a speed shop in Santa Fe Springs (Speed O motive) and the old gent that owned the place said it was a factory piston. I weighed it and it was 20 grams off. I took it back and he said it weighed that because the dome pistons were heavier. I made a bet with him and brought one of each that I had and we went to his scale and they were all the same in weight. I won the bet and he said " in all my years".
Now when we build a block with a new set of after market pistons they all weigh differently and the balance is a must as you know.
I guess I went the long way around not answering your question but wanted to share what I found that made sence while mast producing parts. It makes it easy and fool proof if the are all the same, especially in the areas that we cant identify by eye.

DOM

[Joe C.]

Re: Crankshaft Pilot Bushing Bore

Check this:

http://www.dormanproducts.com/p-25810-14651.aspx?pymmeid=227119

[Joe R.]

Re: Crankshaft Pilot Bushing Bore

Were all pilot bushing bores machined in the same way, or was a final honing process done on those units intended to be installed in engines destined to be mated to a manual trans?

The reason I ask is that I have a spare 680 crank whose pilot bushing bore diameter measures 1.090". It has a mark on its rear flange that suggests it was originally installed in a car with auto transmission.

I'm not familiar with the engine production process, but my first inclination would be to believe that since all 1962-1965 327 engines received the 680 crank, that there would be no need for designating a specific crank to a specific engine.

Hi Joe:

Prior discussions here on the TDB have established that for some reason, two different pilot bushing ODs appear in original cranks, although one of the two sizes is predominant. As I recall, NAPA even has a separate part for the oddball size.

One theory that has been advanced is that cranks from automatic cars were not machined to the final OD, but I don't think this has been found to be consistently true.

I think the true reason for the two different sizes remains unknown, but there definitely were two different sizes.

[Joe C.]

Re: Crankshaft Pilot Bushing Bore

Thanks for the reply, Joe.


To clarify for others who may not have done so, going back to the link that I put up in post #4:

http://www.dormanproducts.com/p-25810-14651.aspx?pymmeid=227119

If you click on "detailed applications" you'll see: "GM conversion from Powerglide to manual trans".

The common Dorman pilot bushing is pn: 690-014, which is 1.093" OD, .593" ID and .750" long. This is the one used for all applications with manual transmission.