MK 3 starter issues

Status
Not open for further replies.
J

jchill

Joined
Jul 31, 2014
Messages
32
Country flag
Hello
I am new to forum

I have the original starter motor assembly ( modified to 4 brush) on my MK 3
Has worked well until recently when starter motor stayed on after starting
I replaced the solenoid and it worked for for about half a dozen starts without issue

However the starter now will engage and spin but doesn't seem to activate the drive gears.
Battery has full charge
Before I remove primary cover and look into the Sprag and bearings ,
I want to make sure that I am not missing anything else
Also Once into the chaincase
I would like some advise on best procedure to determine if it is the Sprag not engaging and what else I should be qualifying
 
Hi, welcome. You've come to the right place. Many MKIII experts here, someone will be right with you. :mrgreen:
 
jchill said:
However the starter now will engage and spin but doesn't seem to activate the drive gears.

Before I remove primary cover and look into the Sprag and bearings ,
I want to make sure that I am not missing anything else
Click to expand...

The sprag is the most likely cause of the problem.

jchill said:
Also Once into the chaincase
I would like some advise on best procedure to determine if it is the Sprag not engaging and what else I should be qualifying
Click to expand...

If you remove the primary cover and then operate the starter Whilst KEEPING ALL BODY PARTS CLEAR OF THE PRIMARY CHAIN AND GEARS, if the large gear on the crankshaft behind the alternator turns but the crank does not rotate with it, then it will almost certainly be the sprag either broken or the sprag elements have 'tipped over' due to wear of the tracks resulting in too much clearance.

https://www.oldbritts.com/e_start_gears.html

I strongly recommend that you also check the overload-backfire slip torque setting.

https://www.oldbritts.com/e_start_backfire.html
 
OK Many Thanks
That's what I thought would be most likely culprit
Its been a few months since I had the case open
but from I take from, your experience I will be able to see the gears unobstructed once I open the case
It may be a couple of weeks before I dive in but will let you know
Again Thanks
 
Commando Cam said:
Jim,
That is an awesome price. I paid about $150 for my last one about 15 years ago.
Click to expand...

I figured it was just a regular industrial one-way clutch so I searched the bearing suppliers I normally use and sure enough VXB had it. I've got one in mine now and it's working well.
 
My experience is that it is not enough to just swap a sprag.
You need to replace all three parts. it means: STARTER DRIVE GEAR F / W NEEDLE BEARING (67T) Part Number: 064731. And ENGINE SPROCKET: Part Number:
064681

Vidar
 
Man, this thread came along just in time. I decided to open up my primary this week to find out the starter problem. Then I saw this thread.

Thanks L.A.B. for the info not contained in the shop manual -very helpful, and JimNH for the cheap part source for sprags, and jchill for starting this thread.

Access Norton rocks! I'm getting my Mk III back on the road soon -after a too long down time.
 
Uncle Nort
It may be next week before I get into my case , so I would curious to see how it goes for you
I would like to know how much or little you had to remove to get to Sprag replacement and backfire check
 
vidar hjelm johansen said:
My experience is that it is not enough to just swap a sprag.
You need to replace all three parts. it means: STARTER DRIVE GEAR F / W NEEDLE BEARING (67T) Part Number: 064731. And ENGINE SPROCKET: Part Number:
064681

Vidar
Click to expand...

This is important... if there is excessive wear, the sprag will fail quickly. Is there an inspection criteria (measurement and surface finish) for the parts?
 
https://www.oldbritts.com/e_start_gears.html
When replacing the sprag bearing, you need to make sure the bearing race in the drive sprocket and the bearing race on the crank gear are not worn and dimensionally correct. The drive sprocket I.D. should be 2.281" and the crank gear O.D. should be 1.625". We do not have the correct tolerances, but within .001" should be adequate.
Click to expand...
 
Uncle Nort said:
Man, this thread came along just in time. I decided to open up my primary this week to find out the starter problem. Then I saw this thread.

Thanks L.A.B. for the info not contained in the shop manual -very helpful, and JimNH for the cheap part source for sprags, and jchill for starting this thread.

Access Norton rocks! I'm getting my Mk III back on the road soon -after a too long down time.
Click to expand...

I found my kickback protection device would not release at any torque within the range of a 250lb/ft wrench! I took it completely apart and found the shaft was galled. I polished everything out and set it to release reliably at 50 lb/ft. I used plenty of anti-seize.
 
I put a factory sprag in recently that I bought about 15 years ago, but have,nt tried out yet. I'm in the process of pulling the primary down again to check the dimensions listed above and to check out the backfire device; none of which I addressed when doing the job the first time. One of the reasons I have so much experience wrenching on my motorcycles is that it seems I have to do everyfreakingthing twice (at least)
Cheers,
Cameron
 
Update MK 3 starter issues

I opened the case and got onto the starter mechanisms.
Per L.A.B email.
I hit the starter switch and the starter gear turned without engaging drive shaft
The Sprag gear was in shambles
There was visible damage to any of the other parts but I will put a caliper on them later to check the dimensions

As a member of US/ Northwest Norton owners I have Old Britts in my back yard
I will give him business on this project as they has ben great in supporting our club and keeping our bikes on road

We only need top read this email to see what expertise he has contributed to this subject
I also plan to check the backfire mechanism using his method of backing off the bolt
Thanks to all I will update again after needed parts are installed
 
Update
I replaced the Sprag, Shaft gear with bearing and it and the Sprag worked as designed

I replaced the case and filled with oil

The bike starts both with electric starter and kick but in both cases;
There is noise from the case, and drag like something is restricting the drive sprocket from turning
You can actually feel the drag or resistance when engaging the kick starter

One theory put forth from a clubmate is magnet is dragging against the retaining bracket
It was also asked if there is a factory specified clearance I can determine with a feeler gauge
I have 2 shop manuals but none make mention of this

Any ideas of what might be askew
I will be opening the case again next week to try to remedy this
Thanks
jc
 
Status
Not open for further replies.

Similar threads

D
  • Locked
Norton mk 3 starter sprag gear jammed!
Replies
8
Views
1,147
Mart UK
Mart UK
C
  • Locked
Mark 3 Starter
Replies
6
Views
892
chasesa
C
Back
Top