Bosch starter motor

[davidwheeler]

If I energise the starter button contact the armature extends and rotates slowly.   If I energise the main battery input, the armature extends and rotates vigorously.   If I energise both, the armature flicks out then retracts and rotates vigorously.
So, on the car it will rotate the crank past one or two cylinders then disengage.  This is fine if she starts immediately but no good if she needs a few cranks.
I did by a clone motor a couple of years ago and it works fine on the car it is on but they are now £1300 which is a lot of money for the second car.
Any ideas?

[simonandjuliet]

Does the motor have a really good earth ?

[davidwheeler]

Yes (it is on the bench)  I have two and both do the same.

[Sebastien]

David,
The Bosch starter is a fine piece of equipment, but when you have problems they become endemic.

The problems are mostly caused by the switch, which is at the back of the starter. When you take off the back cover, and have your starter fixed on the bench, you can see how it works. The appended documents which I was given by Mike Benwell I think, describe the operation. Maybe the spring plate (behind the tumbler yoke in figure 459), which allow the switch to function, is out of alignment, or without sufficient tension. Check also the trip lever function!

Hope this helps.

(PS: The Bosch starter operation was fully described in the LWR Newsletter, try a search on the LWR website).

[Sebastien]

Hello David,

Could you solve your starter problem?

[davidwheeler]

Working on it!

[davidwheeler]

I thought I was getting somewhere.    The later motor, from the 1930 car, worked on the bench once I repaired a broken connection though the solenoid switch was a little reluctant to disengage.    It has the solenoid and the armature advance/holding coil wired in parallel.       The 1927 motor has them in series such that the power to the coil has first to go through the solenoid.   I tried wiring them in parallel instead.     The armature still bounced forward and the back (though if the advance coil is powered by itself the armature advances and stays there).    Moreover, when I took the power off the starter button input, the solenoid switch remained engaged despite not having any power going through the solenoid coil!
I returned to the 1930 motor (which had a different solenoid type) and tried it again.   Alas, bounce out and back again!
I wonder if the motor engages with the flywheel it may stay in position.    The engine is almost reassembled so I shall soon see...
Otherwise, where is your electrician Sebastien?

[davidwheeler]

I consulted with Ribblesdale Auto Electrics and sent them one of my motors.   They told me that the problem is that the knackered pinion was not engaging sufficiently with the ring gear since that engagement is what keeps the shaft extended.   They gave it an overhaul and re-cut the commutator for me.   It runs beautifully.   I put it on the car and discovered that part of the trouble is that when I had the ring gear replaced, the original gear had been turned off with its rim so that the new gear is too far away for the pinion to engage properly.  This does not matter with the replica motor but does with the Bosch.    I am working on trimming the clamp a bit so I can move the Bosch forwards a bit.

[davidwheeler]

Have done and fitted and it seems to work.   I am not sure how tight to do up the nut that holds the pinion on though.