Sprag Clutch

I am preparing to assemble the primary drive on to my '75 Mk III e-start. I cleaned up all the parts and examined them finding the Sprag clutch's outer retaining ring with two full cuts running parallel to two of the Sprags (bearing like figure eights). The "cuts" looked so natural, as if this small protrusion was meant to help keep the clutch locked in the bottom of the engine sprocket...

Well, I found some pictures and realized rather quickly that my Sprag clutch was toast. I called around to see if I could find out why my clutch bit the dust and got a real straight answer at Rabers: backfires and a weak starter.

My question to this knowledge base is: Were the Sprag clutches under speced? Am I going to be looking at $200+ on a regular basis, did I get a bad one? Should I consider kick starting when cold? Is post merger Budwieser as good as pre merger?

I have a real four brush starter, a fresh 14 ybl battery and a Tri-Spark ignition.

RS

I can't really answer your question though I'm sure other more knowledgeable persons on here probably can . I have only 1,000 miles of rxperience with mine . It has what I think is the "Dyno Dave" starter and a Boyer that will soon be changed in favor of a Pazon at Leo's insistence . As a motter of routine I always use my right leg to start it unless I just stalled it or for some other reason don't want to put it on the center stand . Whenever I'm confronted with yet another unexpected , expensive motorcycle problem I usually skip the beer and head straight for a very stiff margarita , thoght I beleve you prefer martini's ? Perhaps my enthusiasm for kick-starting it will be diminished when Leo gives it back to me in it's 880 high compression , ported and cammed form

You could also look on the bright side . My high compression 944 Ducati supersport is hard on sprag clutches too . It has no kickstart option and Ducati only wants something like 600 bucks for a starter clutch .

RoadScholar said:

I cleaned up all the parts and examined them finding the Sprag clutch's outer retaining ring with two full cuts running parallel to two of the Sprags (bearing like figure eights). The "cuts" looked so natural, as if this small protrusion was meant to help keep the clutch locked in the bottom of the engine sprocket...

Click to expand...

Yes those "cuts" in the outer cage were supposed to be there in order to locate the sprag on the "old type" 14 element sprag unit.
The "new improved type" sprags have 18 elements, and the outer cage has a spring clip instead of the cuts.

RoadScholar said:

Well, I found some pictures and realized rather quickly that my Sprag clutch was toast. I called around to see if I could find out why my clutch bit the dust and got a real straight answer at Rabers: backfires and a weak starter.

Click to expand...

If the anti-backfire device has been adjusted correctly? Then the force of any kickback should be absorbed by the anti-backfire device and not the sprag unit. A Tri-Spark ignition should eliminate any backfiring in any case.

RoadScholar said:

My question to this knowledge base is: Were the Sprag clutches under speced? Am I going to be looking at $200+ on a regular basis, did I get a bad one? Should I consider kick starting when cold? Is post merger Budwieser as good as pre merger?

Click to expand...

It's reasonably important that all three parts of the starter clutch assembly are relatively unworn (at least one well known UK Norton parts supplier won't give a warranty on a sprag unless all three starter clutch parts are renewed together.

My Commando's 14 element sprag disintegrated shortly after I bought the bike. I replaced it with an 18 element unit, and correctly re-set the anti-backfire device as a PO had obviously adjusted it so that it didn't slip at all! http://www.oldbritts.com/e_start_backfire.html
And it's been no trouble since, even with a Boyer.

Hey Rond, been there done that. On those Ducati sprags, you can cut a bit off the end of the spring (the "big" end that the small end inserts into) and rescue them a couple times. More details here:

http://www.ducatimonster.org/forums/tec ... -swap.html

It works!

Once they go for good, there is a KTM part at a fraction of the price that is a perfect substitute. PM me if you want details, I have them written down somewhere.

Once again L.A.B. is dead on. The sprag will be destroyed if the antibackfire device is not properly adjusted. Even properly adjusted the shock from the kickback from an improperly timed or fluctuating electronic ignition will destroy it. At $170 each, you want to protect these sprags. The newer 18 dog sprags are somewhat stronger than the 14's.

The inner race and the inside surface of the crank sprocket can often be recovered by glass beading to roughen the surface when replacing the sprag. Truthfully I have only had one instance when the sprag bearing surfaces could not be recovered in this manner.