Mk III Starter Armature Outboard Bush

Last Friday I disassembled the primary on my Mk III to replace the 20-tooth countershaft sprocket with a 22-tooth. While cleaning/inspecting the parts prior to reassembly, I noticed there was no bush in the inner primary cover to support the outboard end of the starter, nor any remnants of one. Closer inspection revealed that the hole in the inner primary was aprox 7/16" whereas the end of the starter shaft was 3/8". In addition, the end of the shaft has become tapered from wear. This explains the heavy wear on the drive side starter bush when I rebuilt the starter last year - no support on the outboard end. I never even thought to check it.

I haven't been able to find a replacement bush in the parts manual - given the wear on the starter shaft it wouldn't be of much use anyway. A pal of mine who owns a machine shop has the pieces now. The plan is to true up the shaft to 5/16" and install a standard oilite bushing in the primary.

Just a heads up to those with a working e-start

jumpjg said:

I haven't been able to find a replacement bush in the parts manual - given the wear on the starter shaft it wouldn't be of much use anyway.

Click to expand...

I believe the early inner primary covers had a separate bush, although this bush was deleted at some point, the starter armature spindle then ran directly in the alloy primary cover, there does not appear to be any change of part number for the inner cover to show this however as a replacement early inner case would possibly have been supplied with the bush already fitted.

The bush is possibly the part labelled as number 3 in group 10 of the parts book, and listed as part 14-6301 although this part is described as a 'nut' but it looks like a bush, and is shown in the correct place?
The BSA Regal (Andover Norton) website also lists the part as a nut superseded part 060355 "Nut 1/4 UNC 14.6301" If there is a 1/4" coarse nut in that area I can't think what it does?....Anyone?

http://www.bsa-regal.co.uk/norton/parts ... 010&Part=3

Re:Bumping Mk III Starter Armature Outboard Bush

Hello
I did a search on e starters and bushes for the 75 Commando.
I have recently acquired one and upgrading the starter with one of Dave Comeau 06-4791B starters.
I see mention of the fact that the inner primary case did have a bushing which may been subsequently deleted and the starter motor shaft just ran in the aluminum case.
Also stated it the fact this can be worn from the starter motor.
My bike is an early 1975, looks to be the end of January, 1975.
The inner primary starter bush has an ID of 15/32". The starter motor shaft is 3/8". So not much support there.
It would seem I could just turn a bush and install it.
Is there a part#? The parts list and diagram are kind of odd. It shows item #3 which looks like a bushing, but is listed as nut and Andover Norton lists it as a 1/4" nut.
Any other information or fixes
Thanks

The book indicates STARTER OUTRIGGER BUSH OMITTED AFTER ENGINE No. 325689.
Your build date of end of January 1975 would put your engine number sequentially after the omission took place so no bush provided.
I don't believe the end of the MGD2044 armature actually is supposed to contact the cover itself, rather to run within the clearance space left when the bushing is omitted.
The armature overhang is insignificant and support by the drive end bush seems to be adequate.
The old parts catalogue does list Ref. No. 3, 14-6301, 21856, as a nut but it sure does look like a bush.
Printed parts catalogues are difficult to correct after having been distributed.
The Andover web site lists it as a bush 064749 at a cost of 78p. Someone has discovered the error and made the correction at some point.
There appears to be no good reason you could not fit a bushing if you desire to do so.
Alignment and size of all the elements involved is critical or you will experience the very reason for which the bush may have been omitted.
All the above is presuming use of the MGD4111 Prestolite unit.
All the best.

Hmm, interesting. I did the AN web search on the part number from the printed list. Didn't click the #3, Duh.
I started down this rabbit hole cause of this statement an the fact of finding no bush installed.
Gear reduction and starter mechanism
Norton/Prestolite
*One huge, but largely unknown defect condition is the worn end of the starter armature shaft and it's mating support bore in the back of the primary chaincase. Many starters are rebuilt without even addressing this issue.
*Unless sealed, the starter suffers when gas infiltration from carb tickling gets inside and washes out lube from the bronze bush bearings. Accelerated bearing wear and harder cranking will occur. The internal gasoline cleaned surfaces will be prone to rusting since rain water is not effectively kept out. Rusting on the armature thrust surface prevents quality rebuilds and is a permanent degrading of the core.
Guess I have to write Dave and see what he is referring to?
Thanks

Further information and a close out of this thread. IMO.
The use of Dave Comeau 06-4791B starters, do not require this bushing or even uses the inner primary support at all.
From the vendor of the 06-4791B starters.
The bushing defect is entirely a prestolite/OEM norton starter issue.
My starter has no extended shaft and eliminates this as an issue. The bushed hole serves no further function.
Dave

Thanks