Starter motor earth route

[937carrera]

Twice in the past few days I have seen postings referring to the oilite bush forming part of the electrical circuit for the starter motor.

That isn't my understanding, and as the bush is supposed to be soaked in oil (which is non conductive) before installation it doesn't make sense that an earth route is populated with something that is non conductive. The bush is there to provide a locating & bearing function for the shaft.

My understanding is that the earth route is via the body of the starter, to the bellhousing and via gearbox / engine earth straps to chassis. When testing a starter you simply provide the earth route to the body (yeah I know you shouldn't really test T25 starters out of the van due to the excess throw)

I'm asking the question because either I need to educated better or the myth needs to be killed.

Over to you guys

[DoubleOSeven]

I’ve been sceptical about the bush being an earth too. Casing to casing for earth, yes.

[Oldiebut goodie]

I have noticed that recently also - in fact there was another post just before you posted this topic.

best diagram I could find at short notice showing solenoid and motor body earths and nothing to do with the pinion and bush:

[R0B]

If it was on farcebook it must be true

[Oldiebut goodie]

Ermmm.......

[T25Convert]

Using the oilite bush as earth would make no sense - the body of the starter is metal, and bolted to the bellhousing, which is in turn earthed. This gives you the ideal opportunity to use standard DC motor design. As an engineer, why would you then decide not to use this connection, but instead use a oil soaked bush that supports a moving shaft to provide the earth connection? I agree that VW were smoking something when the designed the WBX, but I think this is a step to far even for them.

What it does do well is provide support to the end of the starter motor shaft. When it wears, the starter is less efficient and gives the illusion that it is suffering from a poor earth or other fault. As people routinely change the oilite bush when they change the starter, rather than changing the bush to see it cures the poor starting, you can see how it develops that the bush is involved in the earthing....

You can avoid the pesky bush and all issues by adopting a WOSP high output starter - https://www.autoelectricsupplies.co.uk/ ... tegory/224 not an awful price given you get much more oomph for only a few squids more than a recon bosch.

[bigherb]

There is no earth path through the starter shaft it is totally insulated. The earth for the solenoid, armature, field windings goes through the earth brushes to the starter casing.

[DoubleOSeven]

Good. Will stop calling it an earth bush, with immediate effect.

MYTH BUSTED

[937carrera]

Thanks to everyone who contrlbuted