Starter infomation

[240Joe]

If anyone had problems starting last winter despite taking all the normal precautions, you might consider replacing the starter. One of my mercedes diesels always just seemed to turn over a lot slower than the other. And this was the case even though they had essentially identical batteries and clean cables.

A couple of weeks ago I ordered a bosch rebuild from Fastlane and I can't believe the difference in speed the starter turns the engine. The car now starts within a second whereas before it took 3 or 4 seconds even in warm weather.

I'm not sure I understand the failure mode that would cause this but somewhere I read that shorted windings can cause this. I don't know if you can detect this with one of the autozone type starter checkers or not.

Joe

[P.E.Haiges]

240JOE,

The failure mode is: As starters get older, there is current leakage in the armature and field coils thru the insulation. This leakage current decreases the flux of the electro magnets in the starter, and causes the starter to pull more current yet crank the engine slower.

The best way to test a starter is to lock the rotor, apply a certain voltage and measure the torque and current draw. These specifications will be listed in a starter repair manual. I don't know how AutoZone tests starters, but if they don't do a current and torque test, I would be be wary of their results.

To be a "rebuilt" starter, the armature should be replaced with a new or rewound armature and new field coils installed if required. Then it will be equilivant to new. Otherwise it is just an overhauled starter and may not be much better than the used one.

P E H

[leathermang]

I believe there are two starters available which look the same except for serial numbers but with one stronger than the other... So it is possible you now have the stronger one...

[psfred]

Old diesel starters also suffer from excessive resistance in the windings. As the copper gets old and hot (often from excessive cranking), the wire starts to harden and aquire resistance. This results in low current through the winding and higher current draw on the entire starter because the magnetic field is weaker and the starter turns slower. Eventually gets to bad the car won't start and drags the battery down fast.

Turning and cutting the commutator with new brushes will not fix the problem, so a "cheap" rebuild isn't any good, the starter will still be bad after. A new armature is required.

Some folks will know this as "Chevrolet starter disease" -- starts OK cold, but hot won't crank -- same thing, but on the Chevy V8 it is because the starter is only an inch away from the exhaust manifold and it gets baked.

Peter