Converting an MKIII Starter to 4 Pole

dennisgb · Dec 8, 2014

I have an original MKIII starter and I want to convert it to 4 Pole using a Harley Prestolite starter as a donor.

Does anyone know which Harley starter is the right one to use? There seems to be a number of different ones.

I think it needs to have a number that ends in "66" like the following part numbers:

31458-66A, 31458-66B, 31458-66TA

Or Prestolite part number MGL-4004

Anyone do this conversion and know which starter works?

jaydee75 · Dec 8, 2014

I did the HD starter mod a year ago and I used a #31458-66A donor starter. Everything worked fine, trickiest part was moving the brushes to reverse the rotation for the Nort. I don't know for sure about the other numbers, but I think as long as it's a 31458 it will work. Let me know if I can help.
Jaydee

dennisgb · Dec 8, 2014

jaydee75 said:
I did the HD starter mod a year ago and I used a #31458-66A donor starter. Everything worked fine, trickiest part was moving the brushes to reverse the rotation for the Nort. I don't know for sure about the other numbers, but I think as long as it's a 31458 it will work. Let me know if I can help.
Jaydee

Hi Jaydee,

Did you just rotate the brush plate 90 degrees or remove and resolder the brushes?

Ron L · Dec 8, 2014

Did you just rotate the brush plate 90 degrees or remove and resolder the brushes?

No, you cannot rotate the brush plate. You remove the brushes from the holder and rotate them to the next brush holder. On some you may need to solder an extension to the brush lead.

I have done a dozen or so of these. I suggest you consider starting with a new reproduction "Prestolite" HD starter and use the Norton armature and drive end cover only.

I typically turn out the drive end cover for a ball bearing and skim the armature fit the bearing. When fitted with larger cables, it makes for a very reliable starter.

Not to say that Dave Comeau's doesn't function somewhat better (newer technology), but for a stock appearance this is the best alternative and I have used one for the last 12-15 years with no issues on a heavily modified 850. The weakest point is the sprag clutch anyway.

Torontonian · Dec 8, 2014

I wanted the original look , so mailed the Prestolite off to the States for the conversion. Worked great until retirement to joys of Combat punch. 75 Coming out of retirement soon for those retirement years.

dennisgb · Dec 8, 2014

Ron L said:
I suggest you consider starting with a new reproduction "Prestolite" HD starter and use the Norton armature and drive end cover only.

Yes this is the plan. I got a new starter coming. Will see if I can move the brushes as suggested.

Thanks

dennisgb · Dec 8, 2014

Torontonian said:
I wanted the original look , so mailed the Prestolite off to the States for the conversion. Worked great until retirement to joys of Combat punch. 75 Coming out of retirement soon for those retirement years.

This was hard to follow...I take it you were kick starting the Combat and now are going back to electric start

Torontonian · Dec 8, 2014

You better believe it. Dude with 8 lb. cast for 5 more wks. then physio. Low battery on high comp. Combat running Boyer not so good outcome.

dennisgb · Dec 9, 2014

Torontonian said:
You better believe it. Dude with 8 lb. cast for 5 more wks. then physio. Low battery on high comp. Combat running Boyer not so good outcome.

Oh yes I did see you mention that in another thread. Sorry you were hurt...I hate it when the bikes bite us. Fractured an ankle years ago starting my 441 Victor. It's one of the reasons I am trying to get the electric start back on the MKIII.

Torontonian · Dec 9, 2014

I'm holding the Prestolite now and my god I forgot how heavy the thing really is. Add in the gearings and then the bigger battery and we suddenly have an American overweight issue. Hope it won't lead to motorcycle diabetes. :roll:

dennisgb · Dec 9, 2014

Torontonian said:
I'm holding the Prestolite now and my god I forgot how heavy the thing really is. Add in the gearings and then the bigger battery and we suddenly have an American overweight issue. Hope it won't lead to motorcycle diabetes. :roll:

Yes but we aren't racing and looking for the lightest weight...at least I'm not. I bought the Chrome Prestolite HD starter for the extra few bucks...I suppose that one is even heavier

jaydee75 · Dec 9, 2014

Yeah, I took my starter et al off in 1976 when I was a youngster looking for speed. Now that I am old and retired, I am thankful I kept all the parts. I put everything back together last year with the Sportster upgrade and I only kick for the fun of it now. It's nice to have the security of a working pushbutton when needed.
Jaydee

dobba99 · Dec 9, 2014

I converted my original MK3 starter earlier this year by using a new replacement starter for a harley (look for p66a in the part number) ebay will turn up loads of them. As per another poster you will only use the harley frame field, brushes and brush plate. the norton drive end cap will be slightly smaller than the harley frame so you will need to arrange a thin ring shim to make up the diameters. Upgrade the motor cables to a larger size.
Rebuilding your motor to 4 pole or buying a new one will sort the starter motor out but to have total piece of mind you might want to close up the clearances in the sprag assembly. As standard the clearances in the engine sprocket/sprag/drive gear might be okay for an anti-run back device but they need closing up for the duty they perform in starting our engines. This involves sleeving the drive gear with a hardened bearing sleeve and grinding it to the required size (ala the Ken Merrick mod mentioned on the NOC website) Ken stipulated internally grinding the engine sprocket to remove the sprag 'flipping' marks and then sizing the drive gear sleeve to the required size. This isn't necessary as the sprag revolves with the sprocket and closing the clearances up stops the sprag flipping and destroying itself.
If your sprag is still in good condition having this done would be cheaper than having to buy a new sprag, engine sprocket and drive gear at $300 plus WHEN the sprag goes tits up.
Regards
Pete

Torontonian · Dec 9, 2014

Got machining details on that ? :|

comnoz · Dec 9, 2014

I realize the 4 brush conversions have been done for years but I have to wonder why. The stock two brush starter is about all the sprag and slip clutch were designed to handle.
The big problem IMHO is the fact that the standard charging system didn't keep the battery in a good enough state of charge.
When you install a big starter and the battery is hot then the drive is definitely pushed to the limit.

Here is my stock MK3. 27000 miles. Original starter and wiring. The bike has been setting in my unheated garage since the end of July. It has not been on a charger. It was 21 degrees this morning. It has 20-50 v-twin oil in it. If it will start like this on a cold morning then why is a 4 brush starter needed? What am I missing?

[video]https://www.youtube.com/watch?v=rd-N1c7DBlE&feature=youtu.be[/video]

JimNH · Dec 9, 2014

dennisgb said:
Torontonian said:

You better believe it. Dude with 8 lb. cast for 5 more wks. then physio. Low battery on high comp. Combat running Boyer not so good outcome.

Click to expand...

Oh yes I did see you mention that in another thread. Sorry you were hurt...I hate it when the bikes bite us. Fractured an ankle years ago starting my 441 Victor. It's one of the reasons I am trying to get the electric start back on the MKIII.

When I was a kid the skinny guy across the street had a Gold Star. I loved that bike and always watched him start it. He had a method of standing on the starter with one leg and swinging the other down; I've never been able to duplicate it. Anyway, I saw him take quite the ride a couple of times.

Got a Dyno Dave starter; I don't care about the looks as most who look at a Commando these days don't have any idea what they're looking at anyway. It starts like a modern bike, I'm too old to be kicking a Commando.

thackero · Dec 9, 2014

MKIII Starter 2 Pole

I am in the process of rebuilding and reassembling my 75 mark 3 and agree with your comments. I have upgraded the cables and put on a new battery and will fit 2 new brushes/holders. I bought a new sprag for $83 shipped so all is good

8) I do not anticipate any problems if all is assembled correctly.

dennisgb · Dec 9, 2014

comnoz said:
I realize the 4 brush conversions have been done for years but I have to wonder why. The stock two brush starter is about all the sprag and slip clutch were designed to handle.
The big problem IMHO is the fact that the standard charging system didn't keep the battery in a good enough state of charge.
When you install a big starter and the battery is hot then the drive is definitely pushed to the limit.

Here is my stock MK3. 27000 miles. Original starter and wiring. The bike has been setting in my unheated garage since the end of July. It has not been on a charger. It was 21 degrees this morning. It has 20-50 v-twin oil in it. If it will start like this on a cold morning then why is a 4 brush starter needed? What am I missing?

Jim,

The sprag is the weak link, but adjusting the backfire device to the right tension (50 lbs.) seems to be an important step to insure that it slips in case of a backfire to hopefully insure that the sprag clutch is not damaged. Here is a description on this adjustment from Old Brits. The adjustment is 50 lbs to make it slip, not 50 lbs of torque which I think might be a common error.

http://www.oldbritts.com/e_start_backfire.html

I couldn't view your video BTW...it says it is private.

Dennis

comnoz · Dec 9, 2014

dennisgb said:
Jim,

The sprag is the weak link, but adjusting the backfire device to the right tension (50 lbs.) seems to be an important step to insure that it slips in case of a backfire to hopefully insure that the sprag clutch is not damaged. Here is a description on this adjustment from Old Brits. The adjustment is 50 lbs to make it slip, not 50 lbs of torque which I think might be a common error.

http://www.oldbritts.com/e_start_backfire.html

I couldn't view your video BTW...it says it is private.

Dennis

I am vary familiar with the anti -backfire device. They seldom need adjustment unless you have installed a larger starter motor or you are attempting to overcome an over-advanced ignition.

The video should work now. Jim

Jed · Dec 10, 2014

comnoz said:
I realize the 4 brush conversions have been done for years but I have to wonder why. The stock two brush starter is about all the sprag and slip clutch were designed to handle.
The big problem IMHO is the fact that the standard charging system didn't keep the battery in a good enough state of charge.
When you install a big starter and the battery is hot then the drive is definitely pushed to the limit.

You are blessed. Perhaps most other MK3's were made on a Friday afternoon but the notorious starter motor (normally referred to as starter assist) is renown for its imminent failure if left to the 2 pole arrangement
I upgraded to 4 pole using the conversion kit from Norvill (the original was burnt out prior to restoration)
There was bugger all room to fit it together after the extra wires were added and I wasted one sprag as I neglected to grease it prior to installation but the current one has been working fine, it was installed with high temperature grease covering about 40% of the space inside
I know there are differing views on this but it works fine for me and I will be greasing it up every now and then
A properly charged battery is also a must

Jed

Converting an MKIII Starter to 4 Pole

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