Starter motor issues

[Martinwilliams123]

I’m having trouble with the starter motor. It’s a Lucas M418G 25521D.(1952) I’ve removed it and stripped it down as it was turning slow. Can’t see anything wrong and brushes look ok. I’ve rebuilt it now but I’ve got a short across the power terminal and body. I stripped it again and removed the body and still got short. Can anybody enlighten me? I don’t understand why the power terminal is connected to the magnet which is screwed into the body?
Also anybody know where is the best place for buying replacements etc for this car?
Is there a equivalent type starter motor or a modern one to use instead. Thanks

[Zener]

Take it to someone that rebuilds rotating electrics starters, alternators etc , should be easy enough for them and they should be able to give you a quote once opened up , just look online locally

[Penelope Stopit]

Make sure that the brass threaded post from the coils that goes through the commutator end shield has all the insulators on it in the correct places (You probably have checked them already)

Make sure that the two sleeved/insulated brush tails from the coils to the brush box aren't shorting to the barrel or commutator end cover band (You probably have checked them already)

Make sure that the through bolts aren't shorting to the coils link bars where they join the coils together at the drive end (You probably have checked them already)

I may have misunderstood your post but

If you mean that the coils brass threaded post is showing a short to the coils barrel........the coils need removing, un-taping, checking and re-taping if good

If all above is good

The armature needs testing with a growler

How are you checking for a short? The coils and armature have very little resistance due to them being built with heavy copper

This video is possibly worth taking a look at, ok starter is a different model but built the same

[Martinwilliams123]

Using multimeter across the brass thread(power) and the body of the starter motor

[Penelope Stopit]

Martinwilliams123 said:

Using multimeter across the brass thread(power) and the body of the starter motor

With the starter stripped down, barrel on the bench. Brushes, brass post and coil linking bars clear of barrel, testing for coils shorting to earth with a multimeter

Yes there is definitely a short on the coils, might only need new tape and varnish, impact driver might remove the pole shoe screws if you don't know of a workshop with the proper tools

[E-bmw]

Back to your original issue, the turning slowly issue is likely to be a poor electrical connection.

[paintman]

You've got the same question running here:
https://www.pistonheads.com/gassing/topic.asp?h=0&...

You don't say where in the UK you are but if you're in the Leicester area I can recommend these:
https://leicester.cylex-uk.co.uk/company/greens-12...

Not much in the way of a website but IME very good with alternators & starter motors as they've done a few for me.

[Martinwilliams123]

Living in Wales near Neath

[Penelope Stopit]

What resistance reading did the multimeter show?

You obviously know what you're doing but am wondering if you've seen conductivity to barrel body through dirt and possibly moisture or a dead short

Anyway, whatever it is it can only get worse

It's worth removing the coils

[Martinwilliams123]

I’ll double check it but i think it was a dead short between the brass terminal and casing even when the motor was out. I haven’t taken the magnets out yet. What’s odd is that the brass terminal is basically connected to the wiring around the magnet which the magnet is held with a screw to the outer casing. So I’m guessing is there suppose to be a low ohm value between these. Rather confusing.

[Penelope Stopit]

Martinwilliams123 said:

I’ll double check it but i think it was a dead short between the brass terminal and casing even when the motor was out. I haven’t taken the magnets out yet. What’s odd is that the brass terminal is basically connected to the wiring around the magnet which the magnet is held with a screw to the outer casing. So I’m guessing is there suppose to be a low ohm value between these. Rather confusing.

What you are calling magnets are pole shoes, the pole shoes are steel and become magnetised when the current flows from the brass post, through the coils and onwards through the insulated brushes, through the armature and down to earth through the earth brushes fitted to the commutator end shield

[Penelope Stopit]

Martinwilliams123 said:

What’s odd is that the brass terminal is basically connected to the wiring around the magnet which the magnet is held with a screw to the outer casing. So I’m guessing is there suppose to be a low ohm value between these. Rather confusing.

No, the coils are insulated with tape so that they can't conduct through the barrel

Very high resistance to fully insulated between brass post and barrel is to be expected

[Martinwilliams123]

Thanks for the info, must be an insulation issue then. Probably best if I take it to get refurbished then

[Penelope Stopit]

Ok then