Don Terrill’s Speed-Talk

I have on two ocasions run into housings that shrink fit so tight that the bearing races get distorted and cause roughness.
This last case is a worm drive steering box assembly for a sprint car.
It has outer bells in addition to the shrink fit, that could be used with machined spacers to keep the bearings seated.
When the pressure is off the bearings they run free.
Would a sleight polishing of the bores to reduce the shrink fit pressure be wise to do?
All the bearings are being replaced as long as it is apart.

Do you know the OD of the bearing and the ID of the aluminum housing?

I can do some basic calculations and let you know the proper interference fit.

Also, I need to know the general operating temperature of the assembly (i.e. 150 F, 200F, etc.).

Hear are two different sizes used. Bearing OD = 1.850, Bore = 1.846.
The other Bearing OD = 2.000, Bore = 1.997. Both are common ball type.
Material is alum in the shaft housing and I think the worm drive housing may be mag.
T= the average summer track temp of 70 to 90*. The box never really gets hot or swings over to wide a temp range.
Thanks.

You are getting about 0.0011" distortion in the bearing, which is high. You should target ~0.0005" max. distortion in the bearing due to the interference fit. The correct interference fit should be ~0.0015", based on a "medium drive fit/Class H7/s6".


I found a website that has the equation, so I don't have to type it in.

http://www.eminebea.com/content/html/en ... ting.shtml

Greenlght, thank you for the analysis. I thought this was a problem. Now how to do it with out a machineing setup is the next trick.

If I had all of the answers I'd be rich instead of just good looking !!!

Update: The bores have been clearenced, the assembly has be put back togather and back on the car.
Very smooth now.
It was tricky to figure out how to do in small shop but the impossible just takes a little longer.
Thank again.