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M38 pilot bushing

Posted: Mon May 22, 2017 9:31 am
by jsnwalker
A month or two ago, I rebuilt my tranny and ended up pressing a new pilot bushing into the fly wheel. I left it in the freezer overnight and used a brass drift to press it in and it worked great. Got everything back together and now noticed that my rear main seal is blown so I pulled the motor to fix it. When I pulled the flywheel off however, the pilot bushing was quite loose, it could almost slide all the way out on the tranny side and it did completely fall out on the motor side. From what I understand, that bushing should be a real tight fit and shouldn't be able to move around like that? I have driven less than a 1/4 mile since I pressed in that pilot bushing.

You guys think I did something wrong or am I misinformed on how a pilot bushing should function?

Posted: Mon May 22, 2017 9:41 am
by wesk
Did you soak it in engine oil before installing it? I ask because if you didn't and it was snug on initial installation then it would seize or stick to the input shaft and spin making it a skinnier bushing. On the next install insure the new bushing is at least .002 bigger than the hole it goes into and pre-soak it in oil. Then freeze if you wish. It should be driven with a properly dimensioned drift that fits inside the bushing and it's shoulder pushes against the edge of bushing.

A set of these will do the job properly:

Image

Posted: Mon May 22, 2017 9:54 am
by jsnwalker
I didn't soak it in oil but I did wipe some on it when I pressed it in. How long do you say I should soak it before pressing? When I first got the bushing, I believe I measured the OD being .007" bigger than the hole in the flywheel, I'll verify the OD on the new bushing when it shows up.

Posted: Mon May 22, 2017 10:27 am
by wesk
In the old days when you ordered a pilot bushing they would send you a proper oil soaked bronze bushing. Now adays they usually send you a dry brass or bronze bushing. keeps their cost down.

Soak for a full day at least. It helps to set the bushing suspended in a small metal can with the oil in the can and the can sitting on an electric hot plate set to simmer only (not boiling).

Posted: Mon May 22, 2017 1:17 pm
by jsnwalker
Amazing what people will skimp on to save a penny... Thanks for the advice. I'll do as you say when the new bushing arrives. Thanks again Wes.