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STARTER MOTOR Tail Bushing Replacement - SS-114

On 12/11/2017, Mark Wellard in Australia wrote:
".... the point at which a bush should be replaced. My clearances are ~0.010" and I had no idea if this is OK or not. After searching the web, there are some details on sintered bronze bearings  generator repair which suggest the clearance range should be between 0.0005" and 0.0025", therefore I will change mine".

"There is a useful graph (Fig 1) on this web page, giving the tolerances for different shaft diameters":
http://www.sdp-si.com/Design-Data/Porous-Metal-Bearings.php

You might like to review these articles:
UT-103 - The Nature of BRONZE BUSHINGS
UT-104 - Replacing a BRONZE BUSHING
UT-104A - SINTERED BUSHINGS, Initial Lubrication

The Oilite bearings run a thin oil film in the clearance gap, nominally 0.001-inch thick, so the bearing wants about 0.002-inch running clearance (when new). If the load is constantly in one direction (fairly common), then as the bearing wears the inside contour may continue to match the radius of the shaft, thereby retaining the desired 0.001" thick oil film. This can continue to be functional as long as shaft misalignment is not an issue.

Generators and starters, might continue to work okay until the armature starts to touch the field coils, at which time you get nasty gnashing noises and lots of drag friction that can kill the torque. If you notice the bearing is 0.010" oversize when you have it apart, it is a good time to install a new bearing.

You can run a suitable size thread tap into the bushing, then screw in a bolt (or taper threaded pipe fitting) and pull it out. Be sure te new bearing is saturated with oil before installation. Any time you replace a sleeve bearing you should check the running clearance after installation. The process of pressing the bearing into the housing can reduce the diameter or may raise a burr on the end. You should be able to turn the shaft easily with your fingers. If not, then you need to burnish or ream or hone the bushing to regain running clearance.

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