CNW e start conversion, sprag failures

Café au Lait · Jun 20, 2026

robs ss said:
What were the symptoms? Was it off-and-on or a sudden complete failure?

Yep. At first I whirs then catches almost instantly you’d hardly notice. Then I whirs and you need a second press. After that it fails to catch at all when cold but after a ride all good. Then, bollox!! Nada. Kickeroo time and for me with all that luggage that’s none too easy.

It occurred to me that Bill only had it fitted in 2021 (bike built in 2013) so it ain’t lasted long. Replacement is a doddle especially as I’m so effin practised at stripping the primary

Solution? Centre stand and loaded that’s a struggle too as I’m not exactly heavy

I’ve had a few minor issues along the way which I’ll detail in a write up but right now I’m on the ferry supping a cool drink

dobba99 · Jun 20, 2026

MexicoMike said:
I find this all very interesting and curious. BASED ON THIS THREAD the (sprag) issue with the CNW E-start is reasonably well known yet AFIAK, no one posted about it until this thread. Until now no one has ever (that I can find) said anything bad about the CNW E-start.

I have always believed that the CNW was a more robust unit than the Alton (even though I purchased the Alton), but this thread indicates that choosing between the two is more about appearance/price/which potential failure mode is more acceptable!

I think that no one posted about the cnw sprags failures as they might have been under the impression that theirs was a unique failure and not a design fault.
It was only when I saw inside the CNW sprag assembly that the failure mode was built in. Couple that to possibly owners would have been reluctant to admit the sprag failures after they have spent £2500 plus buying the kit that has a built in fault.

Café au Lait · Jun 20, 2026

So are there alternatives that should not fail?

slimslowslider · Jun 20, 2026

It looks like the sprag in the CNW Mk3 uprate version is a Ringspann, with a different shape for the dog bones. Correct?
If so, is that same sprag used in the Mk2 conversion as well?

gortnipper · Jun 20, 2026

johnm said:
. I remember I took some trouble to find the correct lubricant when I installed it but havnt a clue now what I used.

Ask Alan Macy. He knows.

Fast Eddie · Jun 21, 2026

What about dry graphite powder ?

robs ss · Jun 21, 2026

slimslowslider said:
It looks like the sprag in the CNW Mk3 uprate version is a Ringspann, with a different shape for the dog bones. Correct?
If so, is that same sprag used in the Mk2 conversion as well?

Do you know the part number? ...and when did the cNw Mk3 starter become available?

dobba99 · Jun 21, 2026

Café au Lait said:
So are there alternatives that should not fail?

slimslowslider said:
It looks like the sprag in the CNW Mk3 uprate version is a Ringspann, with a different shape for the dog bones. Correct?
If so, is that same sprag used in the Mk2 conversion as well?

robs ss said:
Do you know the part number? ...and when did the cNw Mk3 starter become available?

There is the CNW MK3 sprocket, sprag and drive gear, designed to replace the standard 1975 850 MK3 electric start sprocket, sprag and drive gear.
And then there is the CNW electric start conversion kit for the earlier pre MK3 bikes. Both systems use the same size sprag. The MK3 system uses the sprag as the sprag manufacturer intended. The conversion kit uses the sprag the wrong way and as the kit uses a belt drive, it is run dry, hence the failures.

dobba99 · Jun 21, 2026

Café au Lait said:
So are there alternatives that should not fail?

Not to my knowledge. It isn't the sprags fault, it is the way its used in the CNW e start conversion. If the sprag assembly was arranged like the Mk3 (drive gear snout inside the sprag and sprag revolving with the engine sprocket) the dogbone heel dragging problem wouldn't exist. Also in the cnw e start conversion, the primary is run dry, not good for a sprag in this situation (constant metal on metal contact between the stationary sprag dogbones and revolving engine sprocket snout) you now have a ideal recipe for failure.

slimslowslider · Jun 21, 2026

robs ss said:
Do you know the part number? ...and when did the cNw Mk3 starter become available?

Ringspann SFB 41-13.5/14.
According to their catalogue, it is meant as a replacement for the Borg Warner type BWX 1310145.

baz · Jun 21, 2026

MexicoMike said:
I find this all very interesting and curious. BASED ON THIS THREAD the (sprag) issue with the CNW E-start is reasonably well known yet AFIAK, no one posted about it until this thread. Until now no one has ever (that I can find) said anything bad about the CNW E-start.

I have always believed that the CNW was a more robust unit than the Alton (even though I purchased the Alton), but this thread indicates that choosing between the two is more about appearance/price/which potential failure mode is more acceptable!

I'm a bit surprised too
I've not had any problems with my Alton
Although I did buy it from Yves and I altered his modification to suit my belt drive

Stephen Hill · Jun 21, 2026

I have a CNW E-start kit I purchased 4 years ago from CNW for my 1972 Commando, and so far have not installed it.
Is there an upgraded sprag that I could install at this point, or is the one that came with the kit as good as it gets?

DennisMo · Jun 21, 2026

What about the idea to spray in some dry lube on a regular schedule? I don't know if one can do this with primary cover off only.

robs ss · Jun 21, 2026

DennisMo said:
What about the idea to spray in some dry lube on a regular schedule? I don't know if one can do this with primary cover off only.

I really don't think you have sufficient access.
Also, you have to be careful that any lubricant doesn't have friction modifiers that will stop the sprag from gripping as intended.

robs ss · Jun 21, 2026

slimslowslider said:
Ringspann SFB 41-13.5/14.
According to their catalogue, it is meant as a replacement for the Borg Warner type BWX 1310145.

Do you happen to know if this bearing will fit all cNw e-starts?

gortnipper · Jun 22, 2026

johnm said:
I have always missed the rally unfortunately. Always coincides with my South Island Adventure ride it seems. Been doing that for 8 years now with a couple of old work mates from years ago.

Good to know there are spares in NZ. I have been meaning to get a backup for 5 years now. But my replacement is still behaving. I remember I took some trouble to find the correct lubricant when I installed it but havnt a clue now what I used.

This is the stuff that has the same ingredients as the super pricey stuff recommended by C.M.

slimslowslider · Jun 22, 2026

robs ss said:
Do you happen to know if this bearing will fit all cNw e-starts?

This is actually what I wanted to find out, see question in my post #84.
In the meantime, I learned that this type was used in Mk2 conversions as well, but alas not without failures.

The picture is a still from a youtube video of Jesse's Vintage Garage.
The link to show it elsewhere is disabled however.

johnm · Jun 22, 2026

gortnipper said:
This is the stuff that has the same ingredients as the super pricey stuff recommended by C.M.

Thanks. I probably have the stuff I used somewhere but I have moved house and built a new workshop since then so it could be anywhere now.

robs ss · Jun 22, 2026

slimslowslider said:
This is actually what I wanted to find out, see question in my post #84.
In the meantime, I learned that this type was used in Mk2 conversions as well, but alas not without failures.

The picture is a still from a youtube video of Jesse's Vintage Garage.
The link to show it elsewhere is disabled however.

It also appears that each of the "elements" (not dogbones) is separately sprung. Looks promising given what @dobba99 has outlined as a shortcoming of the cNw starter!
Can't really tell but it appears the elements are activated by torque inertia, but sprung out of the way otherwise.
Cheers

dobba99 · Jun 22, 2026

slimslowslider said:
This is actually what I wanted to find out, see question in my post #84.
In the meantime, I learned that this type was used in Mk2 conversions as well, but alas not without failures.

The picture is a still from a youtube video of Jesse's Vintage Garage.
The link to show it elsewhere is disabled however.

See my answer in post #88
Both systems use the same size sprag
I have one of the ringspann sprags, lent to me as an example (came in a Cross and Morse box) and my impression is that it is too delicate for use in the Mk3 system, given that the engine vibrates i wouldn't install this type of sprag in a Mk3.

CNW e start conversion, sprag failures

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