Bench testing a starter

[Paddy]

I had an old starter and decided to take it apart and "fix it" to be a spare. I saw the problem was a broken insulator bushing that secures the contact. I made a new bushing out of fiberglass sheet stock.

I thought I had learned a lot about solenoids having it a part. The solenoid has two jobs; first drive the bendix to engage the drive gear. Then the last bit of travel, make the high current connection. Driving the bendix is a simple process where the iron slug is pulled in the the magnetic coil. The slug connects to what I would best describe as a teeter totter. The other end of the teeter totter then slides the gear along the shaft. The slug has the compress a spring so when you let off the start key, the slug is pushed away and this pulls the gear out of engagement.

Now to bench testing. I hook up the starter to a battery with jumper cables, Negative the the cast iron housing and hot the the main terminal. Then take a screw driver and energize the coil terminal. The starter pushes the gear in place and motor starts spinning. After 5-10 seconds the gear slowly starts to slide away but motor is still spinning just fine. This makes no sense to me. On the way in the solenoid engages the gear and then makes high current contact. So logically the contacts would break first before the gear retracts when key off. Maybe the friction between the gears would keep in engaged?

Any ideas?

 

[Mendonsy]

What you describe is basically normal operation for a Bendix style starter. The gear requires a load from the initial acceleration or from the flywheel ring gear to keep the spring compressed. Without a load the pinion gear will return to the retracted position.

 

[Paddy]

that is what I hoped! I now have a replacement starter. Thanks for letting me know

 

[jaxs]

You successfully performed work above your pay grade,you are due a raise.

 

[Paddy]

I'm a mechanical engineer so I should be able to fix things. I like the challenge.

Last year, I had a leaking injector pump. Everyone said "just replace the pump, they are nearly impossible to fix". But $10 in O-rings and careful cleaning and it stopped leaking.