Pilot Bushing Tolerance for TKO 600

[cst350]

After Installing a TKO600 behind my Gen 1 SBC I had an issue I traced back to the Pilot Bushing not having enough tolerance around the input shaft. I now need to order a new bushing. Tremec recommends .0005 to .003 clearance once installed. I mic'd out my input shaft at .585 so doing the math I need a bushing with an I.D of .5855 to .588 installed. The available bushings are:

Delco: .59 (1.09 O.D)

McLeod: .592 (1.094 O.D.)

RAM: .594 (1.094 O.D.)

I do not know which I started with (came in a kit) and made the mistake of not measuring it after I installed it the first time. My thinking is that it must have been the Delco part and it compressed when installed.

Does anyone have experience enough to recommend a part that would be in spec after installation. I would rather not make a hobby out of removing pilot bushings, as fun as it is...

[mongocanfly]

Is it apart now?...where you could measure your crank id..

[cst350]

I am re-checking my bell housing alignment. Once I get it set I will take it back apart and measure the crank.

[cst350]

The crank is 1.0910

I got this by measuring the old bushing and then verifying with a bore gauge.

I went to my local parts store and bought a standard SBC/Manual Trans bushing just to see how it measured out. It is not the actual Delco part but matches the PN in their book (no specs of course)

1.094 O.D.
.5915 I.D.

I also verified my bell housing is @ .002 off center. Allowable is .005. So I have to assume that my problem of side loading the input shaft had to be the bushing. Also worth mentioning is that the problem only happened after a few warm up miles. As if the tolerance closes up once warm, witch makes sense

[kwmech]

Is this a real bushing or one of those cheepo chinese pocket bearings? if a bushing, just ream/sand out the inside or have it machined. Is the tolerance overall or per side? .003 would give you .0015 per side, which would be snug when it gets hot. ALSO did you grease up the bushing before installing the trans?

[cst350]

The one I just bought is a NAPA made in the USA bushing.

Good point on the tolerance being half or not, I will contact Tremec on that.

From all I have read I am not supposed to grease the bushing as it is self lubricating and the grease would block that process

[cst350]

This was the response I received from Tremec after forwarding them all of the above info and measurements...

Hello
Our company does not make or supply pilot bushings. This is a question you should ask the supplier you are ordering from.

I deal with manufacturing engineers every day (think bottom up, custom mountain bike builds)

I have never had an engineer avoid answering tolerances on their own parts.

[SidsChopShop]

FWIW- I installed a Napa pilot bushing in 2017 when I built my 355. When I installed my TKO this past winter, I left the bushing installed and used it with my new transmission. I can't remember the exact measurements but I believe the bushing was .003 larger than the input shaft. So far I have over 2000 miles on it since March and I haven't had an issue.

One more thing, make sure you get the correct bushing. 283 (and probably including 327) had a different size bushing than the 350 cranks. Napa should be able to provide both bushing to compare. Good luck

[cst350]

Thank for the insight. I went with the Delco which i measured at .590 installed. My input shaft is .587 so it should work (on paper!)