4577 crankshaft pilot bore

[Timothy B.]

Last week I posted a picture of a crankshaft I wanted to ID and this crank had the numbers 4577. I checked the pilot bore because I want to install a new bushing and it mic's at approx. 1.084" and the depth of the finish lathe cut is only 5/8 deep, therefore the old bushing stuck out 1/8". I will post a picture of the old bushing and you will clearly see why I need to replace it. Has anyone ever encountered this situation and can shed some light on why this crank has a small bore pilot hole. According to what I have read the pilot hole is supposed to be 1.092".
Thanks for any help, Tim Barbieri

[Timothy B.]

Re: 4577 crankshaft pilot bore

Picture of damaged pilot bushing, you can clearly see where someone drove this bushing in the crank.

[Loren L.]

Re: 4577 crankshaft pilot bore

I think you'll find that to be a pretty good indicator that the crank started life in a car with an automatic transmission

[John M.]

Re: 4577 crankshaft pilot bore

I had a similar problem with the diameter of the bore. It was 1.072 so after trying to force the 1.094 bushing in and failing I put the next bushing on a fixture and turned it to 1.074, pressed it in and all is good. I'm still P--D off with the engine builder who knew it was supposed to be for a 4 speed.

[Joe L.]

Re: 4577 crankshaft pilot bore

Tim-----

The fact that the bushing "sticks out" about 1/8" is not a problem; that's how they are supposed to be.

[Timothy B.]

Re: 4577 crankshaft pilot bore

If the crank is from a automatic car, does the pilot from the torque converter sit in the outer recess and that's why the inside hole is not finished to the 1.094 bore? I read that the 4577 crankshaft is a replacement for 62-65 SHP and 3884577 is 66-67 327 all, is the difference the journal treatment and damper hole and why the change in part # from the 2680 and it's long number?

[Mike McKown]

Re: 4577 crankshaft pilot bore

I just built a 327 this past year. I used a 4577 crank. The crank was a core so I have no idea what it's application was. I didn't check the bore but a standard bushing knocked right in. You're not the first guy that's found a smaller than expected pilot bore but I have no idea why unless maybe a truck, marine or some other application calls for an off standard automotive size.

[Duke W.]

Re: 4577 crankshaft pilot bore

The 4577 crank forging went into production circa 66, replacing the 2680, and was finished to both medium performance (300HP) and SHP/FI spec as was the previous 2680 forging. I don't know the actual differences, but as with many later production parts, the two finished cranks based on the 4577 forging became the service replacements for earlier engines that originally had 2680s.

AFAIK finished crankshafts to each spec from either forging are of equal durability.

SHP/FI cranks from either forging had a Tufftride surface hardening process, which improves high rev durability and has the nose drilled and tapped for the 8" balancer center bolt; the 250/300 HP cranks from either forging do not have these two features.

Duke

[John H.]

Re: 4577 crankshaft pilot bore

I've only heard about a few of these situations over the years, but the engine plants must have screwed up more than a few; NAPA has a bushing specifically listed for use with a "Powerglide 1.06" crank" hole (their #690-034, $2.77). I've seen the small-block crank drawings, and all call for the same standard machining for the GM pilot bushing, regardless of their ultimate application. The only exception is for the '57-'58 passenger cars with Turboglide - that converter has a HUGE pilot on the front, and required a unique crankshaft with a HUGE machined pilot hole in the flange.

[Joseph T.]

I ran into that crank problem

John..many years ago I bought a '57 548 engine as a stand by. Years later ..I decided to have it rebuilt. Once I got it home and attempted to attach the 4-spd transmission..I could see a big problem.

The crankshaft that was in the engine and re-used was for an automatic only.

I did some research and found an article in a late 50's car magazine discussing the very same situation...and as I recall a special pilot bearing was available to solve the situation.

In my case.. I took the engine back to the rebuilder and had the crank swapped out for the correct application for the 4-spd.

I remember the shop where I bought the engine..and at that time they were working on a 57 Cameo.. Maybe the engine came from that vehicle.

I always wondered if I should have kept that crank.

Joe