Mk3 sprag repair

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I read on this sit about fitting roller bearing inner and outer races to build up the dimpled surfaces on the gears to fit a new sprag bearing.
But I can't find the post.
Can anyone advise me on the sizes to do this?
Anyone done this and was it successful?

Regards
Graeme
 
Hello Graeme

Here are machining details for the drive gear sleeve mod

The Mk 3 starter system can be made to reliably perform like a modern bike, so much so that i,m seriously considering removing the kickstart altogether and the bonus of that being i can then make some rearsets that don't have to accomodate the kickstart so can be neater in apperance
This mod increases the angle of the sprags so it has no chance of 'flipping' and consequently wrecking the sprag/drive gear/sprocket
Obtain a LRT354220 hardened bearing inner race from your local bearing stockist (should cost only a few pounds, I got two for less than a tenner)
Turn/grind the drive gear spigot (what engages with the sprag) down to 1.450" diameter. make sure you have a good radius tween the spigot and gear i.e. NO UNDER CUT You can do this with the needle roller still in place, just plug the bore
turn/grind the bore of the your new inner race so it has an interference fit of 0.002" (1.448") chamfer the bore so it will sit over the radius
Press the two together ,remount in the lathe and turn to length.
Turn/grind the OD down to 1.632" (this is an increase of 0.007" over standard)
radius the end so it is an easy fit in the sprag.
Job Done
Ken Merrick did his mod a little differently, he glued the sleeve to the drive gear with loctite retainer. He also internally ground out the engine sprocket to remove the sprag dig in marks (approx 0.010") and increased the size of the sleeve accordingly. I have found that it is not necessary to do this.
Even if you have to pay someone to do the machining for you it should work out cheaper than replacing crunched bits for new ones.
The drive gear and bearing sleeve can be turned with sharp carbide tools but I used a toolpost grinder to finish the diameters (Same toolpost grinder i used to reface the cam followers)
My last commando (thirty years ago) crunched its sprag in Stockholm (Sweden) when I was going to the Britti Ralli in Finland. Thank goodness for kickstarts! That bike had a two pole starter. This was years before I got myself a well equipped machine/workshop.

I have since done this modification for a number of people and i now use the inner race from second hand bearings removed from overhauled industrial gearboxes. Although this requires removing more metal to get the sleeve to the right diameter.
I have also converted brand new harley davidson starters to fit the mk3 commando. I have one of these on my MK3 and since i got her back on the road in april last year i have not used the kickstart at all, and up until january of this year she lived outside even down to subzero temperature, and she still started on the button.

Belt drives run dry, and this starter system do not mix well. The sprag requires lubrication or it will prematurely fail, If it fails and seizes the sprocket to the drive gear you will kiss your motor goodbye as the starter motor will not be able to withstand the huge increase in revs (60,000 plus) If you do have to run a belt drive make sure it can run in an oil bath (with oil!)
I run a duplex chain on my Mk3 primary drive as according to Andy (the chainman) No one makes decent triplex chain anymore.
Regards
Pete

dobba99
Posts: 40
Joined: Sun Jan 26, 2014 1:34 am
Location: Yorkshire, England
 
Thank you Pete,
I'll get the inner race and go from there.
Regards
Graeme
 
Pete,
Did you use the original 14 tooth sprag bearing or the 18 tooth one?
 
Graeme.
Cannot honestly remember if mine is an eighteen or fourteen, probably a fourteen. some sprags have a couple of thin bronze springs in the middle which look like centering springs, these can be removed if they cause binding on the new larger drive gear spigot.
My Mk3, which I call Mitzi, (Ogri's girlfriend in the cartoon strip) starts far easier than my girlfriends 2014 Bonneville which annoys her something rotten.
Why Mitzi i hear you ask. Thats because when i was younger we all wanted to be like Ogri and now i get to ride Mitzi when I like!
Mk3 sprag repair


This is Mitzi
 
Just had my fourth sprag failure in 9000 miles Two high dollar 14's, two 18's. The last time I replaced the sprocket as well. It looks like I will be kicking it for a good while
 
CNW is going to offer a high quality replacement set for the MK3. Once that is available, I'll resurrect my MK3 starter drive.

Glen
 
Hey Guys,

We are in fact, together with STS in Florida that are building our pre MkIII e-start kit, working on a MkIII e-start partial upgrade. It will consist of a different front drive sprocket and a crank gear. These parts will be drop in replacements and tolerances and more importantly, material quality will be very different than what was used on the stock machines. This to ensure that the wear that we find on virtually all MkIII's engagement surfaces will not be happening.

These parts are on deck to be developed and manufactured. We know that some are anxious to get their hands on these but we have to get some other things behind us before we can focus on these. I cant say when they will be ready to go as this always gets me in trouble (time flies at warp speed in my world)

Matt / Colorado Norton Works

www.coloradonortonworks.com
 
A note from STS. We have been analyzing the Mark 3 sprag components. We have done some nondestructive, and destructive testing of components that commonly fail.

We are somewhat shocked at what we have found. Both the materials, and more importantly, the heat treat procedure for these parts (stock OEM) are terrible. It is surprising that proper materials and heat treating techniques were available in the early 70's to produce much better sprag components than what were manufactured.

The sprag (18 tooth) on the new pre Mark 3 E-start is performing quite well on the test bikes. Last inspection of the sprag components was at 2000 starts, and everything looked great. Matt should be shipping out first assemblies of pre Mark 3 e-Starts by the end of April. He already has many of the billet aluminum components (inner primary, starter mount plate, and starter mount cover) and is in the process of putting the CNW "SHINE and POLISH" on them. All the rest of the aluminum components are at anodizing now. The sprag and drive gears are at heat treat.

Next is the Mark 3 upgrade, and an ignition interfaced, anti-sump valve.
 
Hey G81,
Have you tested the replacement Andover supplied sprocket and sprag ?
The original one I just replaced had big indentations in it from the sprag , just wondering if the replacement will be just as bad .
cheers
 
ausnorton said:
Hey G81,
Have you tested the replacement Andover supplied sprocket and sprag ?
The original one I just replaced had big indentations in it from the sprag , just wondering if the replacement will be just as bad .
cheers

All of the samples we tested came from Matt at CNW. I believe they were original equipment on bikes, but Matt would have to confirm

If anyone has any Andover sprag components that we could test, I would be happy to do it. But, it would be destroyed in testing.

John
 
ausnorton said:
Hey G81,
Have you tested the replacement Andover supplied sprocket and sprag ?
The original one I just replaced had big indentations in it from the sprag , just wondering if the replacement will be just as bad .
cheers

Hey,

As John mentioned, the parts sent to STS for hardness testing were all original, 1975 MkIII parts

We do not know if the new production parts available are made ay differently than the older versions nor do we intend to find out. As mentioned, testing these parts will destroy them and it doesn't make any sense for us to buy new parts to do this since we already decided we will be making our own parts

We are making a replacement kit that will outperform the originals. That's our goal

Matt / Colorado Norton Works

www.coloradonortonworks.com
 
Matt/cNw -

I definitely want a set of the new and improved e-start parts for my Mark 3 - the crank gear and drive sprocket.

My kick-starter has been gathering dust on a shelf for some time, but just a few days ago when I hit the starter button, the e-start system just spun. It caught on the third try and turned the engine over, but I know where things go from here - downhill.

Really don't want to buy a crappy original stock crank gear and drive sprocket .... again. (Yep, been here before).

So, for all us Mark 3 riders with this weak link in an otherwise functional system, asap would be nice for the new parts.

Just sayin,
 
dobba99

Thanks Pete, your solution work very well.
Thank you very much.

Regards
Graeme
 
I took a divot out of my shin again yesterday, kickstarting my Mark 3 with rearsets.

A few weeks ago I had to re-install my kick-starter which had been stored in a box for the last couple of years.

However, my sprag has failed.... again (didn't open the primary yet, but I assume that is the case).

I have replaced it at least 3 times, and yes, the last time I replaced the drive sprocket (06-4681) and the starter crank gear (06-4731) as well.

I now have a box with 3 old sprags, two old drive sprockets and one old starter crank gear.

I am not going to buy another drive sprocket and crank gear. I'm done with spending money on parts that fail (and yes, my anti-backfire device is functioning).

My son is a machinist, working in a high-end shop making medical devices, aerospace parts, etc., and has offered to make me a new drive sprocket (haven't pitched him on the crank gear yet).

My question: does anyone have the CAD or SolidWorks file or even paper specs on this part? And the spec on the steel itself (will make it harder than stock, but need to know the stock spec.

Otherwise I can buy a new one from CNW when they have them available, but I'm tired of taking divots out of my shin bone in the meantime.

Anybody got the specs?

Many thanks.
 
Hi
Yes, we are more out there waiting for the final solution.

It has been quiet from Matt / CNW for a while now regarding this system.
I had hoped that this winter would be the time I got innsalert the final solution:)

Vidar
 
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