Mk 3 Sprag not engaging.

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hillbone

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Hello.
Help please.
Her'es what we've done.
Replaced everything. Read everything. Checked everything..again and again. Reviewed everything on Old Britts site on assembly. Manually hand held the assembly and the sprag engages. Hand twist the assembly in situ and the sprag engages.
I have the newer starter motor fitted in place of the old black one.
The problem is that everthing just spins and the sprag will not engage when activated by the starter.
Driving us all nuts.
Some clues please. Hillbone
 
Hi Good Call. Checked that 1 first. All good. Everything spins in the right direction, the sprag just doesn't grab when spun by the starter.
 
Try some abrasive wet 'n dry paper in the engine sprocket where the sprag engages and roughen the surface up a bit. If this contact area is polished smooth it may be causing the sprag to not grip. Obviously I'm not talking about scrubbing several thou off!

"dobba99" from this forum gave me this tip as my sprag was occasionally just spinning and not engaging and it seems to have cured it.
 
Will try that mate.
I noticed the old original starter motor runs has a different number of teeth on the drive than the newer more compact starter. Is it possible the newer starter is spinning too quickly for the sprag to catch? I know I'm clutching at straws here.
 
Reggie said:
Try some abrasive wet 'n dry paper in the engine sprocket where the sprag engages and roughen the surface up a bit. If this contact area is polished smooth it may be causing the sprag to not grip. Obviously I'm not talking about scrubbing several thou off!

"dobba99" from this forum gave me this tip as my sprag was occasionally just spinning and not engaging and it seems to have cured it.
Click to expand...
+1
I ran 600 wet and dry lightly over both surfaces on mine never missed a beat.
What oil are you running in the primary?
 
My system ( D.C. faster starter ) will not engage when cold , just spins. Warmed up it works like a charm. Suspect backfire device ?
 
Did you happen to grease the sprag? That will cause it to slip.
I would also check the inside dimensions of the drive gear where the sprag grabs against just to be sure.Somewhere on the forum I believe LAB posted the numbers.
Pete
 
Reggie said:
Try some abrasive wet 'n dry paper in the engine sprocket where the sprag engages and roughen the surface up a bit. If this contact area is polished smooth it may be causing the sprag to not grip. Obviously I'm not talking about scrubbing several thou off!

"dobba99" from this forum gave me this tip as my sprag was occasionally just spinning and not engaging and it seems to have cured it.
Click to expand...
Reggie,
Are you saying that the internal surface inside the crank three tooth sprocket and the external surface on the starter gear wheel should both be roughened up ? I have ordered a new sprocket so no need to prep that surface however I plan on reassembling with my old starter gear wheel as the OD is within spec however the surface is mirror finish at present. I have put a lot of money in my electric start mechanism so do not want to mess up. I have a new sprag and new needle roller bearing and sleeve for the starter gear wheel.
Thanks
Oscar
 
Torontonian said:
Suspect backfire device ?
Click to expand...

However, when the anti-backfire device slips, it makes a loud rattling noise (similar to an impact gun).
 
thackero wrote;
Reggie,
Are you saying that the internal surface inside the crank three tooth sprocket and the external surface on the starter gear wheel should both be roughened up ?
Thanks
Oscar
Click to expand...

Yes these are the surfaces that I am referring to, but I wouldn't rough up any of the surfaces for the sake of it unless you are having problems such as described i.e. you press the starter button and all you hear is a whirring noise and the engine doesn't attempt to turn over which is when the sprag doesn't mechanically engage with it's two surfaces faces. Having said that it shouldn't harm anything as long as you go at it sparingly.
 
The colder weather whirrings force me to reverse kick and hit the green button and open the tickled throttle a bit all at the same moment. Ah , Nortons. Warm up , then hit the starter button for full sprag engagement every time. Vroom. :wink:
 
Hi.
These are new parts so the surfaces should be polished smooth. I am not using ATF but a 20w50 in the case and definately no grease. Theres no chatter from the backfire device as it was checked as well. All i get is the whirring from the gears.
I will try the wet and dry later when i get to pull it apart.....again.
Thanks everybody.
 
A lot of years ago, well before the internet and forums were so popular I experienced the same issue with a MK3 sprag that seamed fine but spun freely without ever grabbing. I still have what I think is that original sprag. It has 14 dogs and the one I replaced it with years ago had more, maybe 16 dogs or so. (Though it's possible the original had only 12 dogs and the 14 dog one is newer) Point is, it looked fine but slipped. I don't remember what I was using in the primary at the time but it may have been automotive 20w50. At the same time I replaced the sprag I started using motorcycle specific oil suitable for wet clutches and sprag starter drives. No problem since. Perhaps auto oil with friction modifiers is just too slippery for a Norton sprag clutch. If you are using auto engine or something else in your bikes primary, a relatively simple try would be to clean every thing in the primary with brake degreaser then refill with a good 20w50 bike oil. I use Mobil 1 V Twin.
 
Biscuit said:
A lot of years ago, well before the internet and forums were so popular I experienced the same issue with a MK3 sprag that seamed fine but spun freely without ever grabbing. I still have what I think is that original sprag. It has 14 dogs and the one I replaced it with years ago had more, maybe 16 dogs or so. (Though it's possible the original had only 12 dogs and the 14 dog one is newer) Point is, it looked fine but slipped. I don't remember what I was using in the primary at the time but it may have been automotive 20w50. At the same time I replaced the sprag I started using motorcycle specific oil suitable for wet clutches and sprag starter drives. No problem since. Perhaps auto oil with friction modifiers is just too slippery for a Norton sprag clutch. If you are using auto engine or something else in your bikes primary, a relatively simple try would be to clean every thing in the primary with brake degreaser then refill with a good 20w50 bike oil. I use Mobil 1 V Twin.
Click to expand...

I do not believe Mobil 1 V-twin is JASMO MA so it may not be the best thing for you clutch plates. I realize the plates are not submerged in the oil, but they still get wet after use. Vavoline 20-50 MC oil is JASMO MA and is cheaper. I do use Mobil 1 in the engine.

Pete
 
Deets55 said:
[

I do not believe Mobil 1 V-twin is JASMO MA so it may not be the best thing for you clutch plates. I realize the plates are not submerged in the oil, but they still get wet after use. Vavoline 20-50 MC oil is JASMO MA and is cheaper. I do use Mobil 1 in the engine.

Pete
Click to expand...

Well you are right about the JASMO bit. Not a mention of that on the bottle but it does mention being good for transmissions and clutches so I'm guessing sprags would fall right in there too. Always something to think about, jeeze.
 
Always something to think about, jeeze.[/quote]

Or over think. I am guilty on all counts here. Wait let me think about that..........................
 
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