Carbon residue on the starter commutator

[DIYspanner]

Can this cause the brushes to stick to the commutator so the starter can't rotate or cause poor contact so the starter is sluggish?

The car in question is a 2004 Bora TDI by the way!

 

[Burnerman]

Unlikely the brushes would stick, but the segments on the commutator should be clean-ish.
If the starter is lazy, more likely to be the connections or the battery earth.
John

 

[DIYspanner]

Unlikely the brushes would stick, but the segments on the commutator should be clean-ish.
If the starter is lazy, more likely to be the connections or the battery earth.
John

Thanks John!

Here's a cracking good video for servicing a starter which is either the same or very similar to that on the Bora!

 

[DaveHerns]

Bearings might have dried out and need a bit of lube.

 

[Keithmac]

I've done a few bike starter motors where the carbon dust has packed in between the comutator pads and basically caused a short circuit which considerably slowed motor down.

Cleaned the "valleys" out with a razor blade and starter worked correctly again.

When rebrushing a starter I always clean the comutator pads back to shiny copper (very quick touch on the bench polishing wheel).

 

[magicmushroom666]

I've found its more the brushes sticking inside their holders causing them to no longer be sprung into the commutator that causes the problem with motors.

 

[DIYspanner]

Bearings might have dried out and need a bit of lube.

I'm presuming ceramic grease would be better for the job than bearing grease to cope with the engine heat?

The fella in the video above coats the bush with oil but oil would run leak out, grease sticks and stays put.

 

[Peter.N.]

If its a starter with a reduction gear, lack of grease in that will slow it down considerably.

Peter

 

[Keithmac]

I've found its more the brushes sticking inside their holders causing them to no longer be sprung into the commutator that causes the problem with motors.

Yep sticking or worn out brushes are most common failure but worth cleaning comutator pad gaps out as a matter of course.

I've done 3 2010+ R1 starter motors now, brushes free and good length but shorting caused by carbon dust between the pads.

 

[DIYspanner]

So basically

Clean/polish the commutator segments and the gaps.

Clean the brushes and brush holders.

Clean/lubricate the reduction gear set.

Lubricate the bushes.

When checking the armature, I presume from brush position, opposite commutator segments should have continuity?

My normal cleaner is 1" paint brush and petrol in a Fray Bentos tin!

 

[Burnerman]

Traditionally the bushes are made from Oilite - a sintered porous phosphor bronze. They need to be soaked in oil before use.
John

 

[DIYspanner]

A cracking video on armature windings.

 

[DIYspanner]

Well it seems the culprit was the battery for the intermittent slow cranking on the Bora.

Got the call this morning to go and assist cause it wouldn't start.

12.4v across the battery according the multimeter but when trying to crank, it dipped to about 5v which is evidence of a dropped cell or two.

Jump leads on from my TDI and it fired straight up.

New 70A Numax brand battery from the local factors and the engine's cranking like a good 'un.

 

[Burnerman]

Dropping to 5v
That sure is low!
John