SPRAG CLUTCH OPTIONS

nznorton · Nov 18, 2013

Hello fellow MK 3 owners,,

Yesterday I opened up the primary on my MK 3 and removed the remains of the sprag clutch ,, I have had problems with the electric start so I thought I would have a go at working out what was wrong with it's operation, as you can see by my images it wasn't hard determining the problem !,,

My questions now are: I have heard on this forum that there is a new updated version available that has 18 rollers as opposed to the original 14, I have found a new unit but it is the one with 14 rollers, would it be better to try and find an 18 roller version or take this 14 roller that is available now? (also pictured below)...

Does the overload backfire devise assembly ever give trouble, in other words do I just refit it as is or does it need looking into ??

Is there any reason why I can not fit up a new sprag to the drum without removing it from the shaft as recommended in the workshop manual ? ...
Can someone advise me on who has the most reasonably priced sprags either in the US or the UK ...

Thanks for your help
Paul

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Ron L · Nov 18, 2013

I have used both the 14 and 18 dog sprags on my e-start café racer and both worked fine until they broke. I can't say one was better than the other and I attribute both failures to an improperly set anti-kickback device. If you search this forum you should find a thread on how to properly adjust this device so it will slip before the unit over torques the sprag and breaks the cage. Several I have checked are tightened to the point at which they will not slip.
It might also be beneficial to use a new pair of Bellville washers and adjust them to slip at no more than the recommended maximum of 50 ft/lb.

comnoz · Nov 18, 2013

The sprag clutch fails because they don't receive enough lube. The spag element is in light contact with the center race when the engine is running. That causes wear to the inner race and the end of the sprag element. When the element or the inner race has worn enough then the element can flip over.

I have not found the 18 element sprag to last any longer than the 14 element sprag.

If you want to make the sprag last longer you would need to come up with a way to get more oil to it. Jim

Hobot · Nov 18, 2013

Chain throws oil on case to drip down, so maybe a flange or even a wick like dangle could direct oil on the vulnerable dryness.

AntrimMan · Nov 19, 2013

nznorton said:
Hello fellow MK 3 owners,,

My questions now are: I have heard on this forum that there is a new updated version available that has 18 rollers as opposed to the original 14, I have found a new unit but it is the one with 14 rollers, would it be better to try and find an 18 roller version or take this 14 roller that is available now? (also pictured below)...
It makes little difference as far as reliability. Cost would be my guidance.

Does the overload backfire devise assembly ever give trouble, in other words do I just refit it as is or does it need looking into ??
The overlaod device would eventually slip more easily if it was constantly overloaded. The balls would wear ramps into the edges of the driving holes.
You can get creative and test the breakaway torque, see the Old Britts website for hints.
The entire estart drivetrain is a hodge podge that only works in between breakdowns. That's just the way it is.
Have you noticed how the triplex chain makes contact with the OD of the inner thrust washer on the overload device?
Any event that powers the crank to rotate in the wrong clock direction is to be avoided.
Old Boyer's and low battery voltage are to be avoided.
Even If you only use the kick start alone and it kicks back the damage is being done.

Is there any reason why I can not fit up a new sprag to the drum without removing it from the shaft as recommended in the workshop manual ? ...
The breakage of the sprag cage has likely been accompanied by a myriad of little dents to the inside of the sprocket race and also the crank gear shaft OD race. The inside race of the sprocket has a close tolerance and when worn oversize may allow the sprag to over travel and then jam.
If you are comfortable with simply replacing the sprag assembly itself then do so. The other two items are costly.

Can someone advise me on who has the most reasonably priced sprags either in the US or the UK ...
A forum member named norton dave (IIRC) had recently offered the sprag at a very reasonable price, he is located in the southern hemisphere, not UK or USA.
The sprag assembly itself is a standard industrial item available from bearing houses, the sprocket and gear are particular to the MKIII.

While you have it unbuttoned you may as well clean the clutch plates too.
All the Best.

Thanks for your help
Paul

Jeandr · Nov 19, 2013

Alton is coming up with a kit to replace the fragile bits in the original ES Norton, it could be worth the wait instead of putting back parts that may not last any longer than the originals.

Jean

Chili · Nov 20, 2013

Question to Jeandr, is there any time line on the Alton parts for the ES ?
Peter

Jeandr · Nov 20, 2013

Chili said:
Question to Jeandr, is there any time line on the Alton parts for the ES ?
Peter

Last time I asked, they said soon and soon came to pass :wink: I know they are very busy putting the starter kits together. I will send an e-mail to Alton and ask again.

Jean

nznorton · Nov 21, 2013

Thanks Jean on behalf of many other MK3 owners awaiting a better answer to this age old problem..
I hope you hear from Alton soon

Chili · Nov 21, 2013

I to wish to add my thanks Jean, I don't want to push the designers at Alton, for I have a couple of sprags spare, but I wonder if I need to replace the inner & outer parts of the the start gears?
Again many thanks.
Peter

Jeandr · Nov 21, 2013

They have designed a kit to replace most of the parts with updated ones, I think they also reccomend changing the starter motor.

Jean

Chili · Nov 21, 2013

Hi , and thanks,
I have already replaced the stock starter motor, with an Alton, spins fast, but the sprag does not seem to open out and grab,when cold, so I believe that the wear may have been too great (it did work for a while), to begin with I did put a too heavy grade and sticky oil in the primary, since flushed. Now the srag just spins, unless I have had a long run and the engine is warm, then the starter works ? This is on a Mk 111 ES.
Peter

Jeandr · Nov 21, 2013

Chili said:
Hi , and thanks,
I have already replaced the stock starter motor, with an Alton, spins fast, but the sprag does not seem to open out and grab,when cold, so I believe that the wear may have been too great (it did work for a while), to begin with I did put a too heavy grade and sticky oil in the primary, since flushed. Now the srag just spins, unless I have had a long run and the engine is warm, then the starter works ? This is on a Mk 111 ES.
Peter

You probably have a Dave Comeau starter, that is the starter Alton reccomends with their MKIII kit

Jean

Chili · Nov 22, 2013

Jean, I bought it from Alton, so I guess you are right, but how do I find their upgrade kit?
Thanks for your input.
Peter

Hobot · Nov 22, 2013

For those that have been through the cycle of ruined sprags, might be worth a try to have the wear prone parts cyro tempered, maybe by the -400'F method rather than more common -300'F process. I was darn impressed by chain saw teeth edges lasting like 2-3x longer throwing chips instead of dust and the chain/bar tension stayed w/o adjusting. There is also the various dry friction spray on coatings of like Ti-oxide but its thin and does get rubbed off with use. Friction plates in oil often have a friction additive like Ford Type F ATF, so maybe could find what that is to add to thick enough oil to work tensioner but spare cleaning plates rather longer.

Bernhard · Nov 22, 2013

Just an observation; the chaincase looks remarkably clean of chaincase oil?

nznorton · Nov 25, 2013

Hi Bernhard,,

I wiped up and cleaned all the old oil out as it had a strong strange smell to it..
Has anyone had an update from Alton on the MK3 up-grade,, I wrote to them last week but have not received a reply ..

Cheers
Paul ..

SPRAG CLUTCH OPTIONS

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