CNW e start conversion, sprag failures

Stephen Hill said:
Not to discount the above information, but it is worth noting it is AI generated.
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DennisMo said:
I have an Alton. Its' dog bones are not in constant rotational contact compared to the CNW design.
However, I have learned a lot in this thread and the CNW sprag is simply a maintenance item.
I would buy it. They make great kit.
Dennis

I found the following on-line. It seems that some (or maybe all) sprags are designed for constant rotational contact

These are results for should sprag clutch dog bones always be in contact with rotating parts or be retracted by centrifugal force
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Sprag clutch "dog bones" (or sprags) are typically designed to maintain constant contact with the inner and outer races. They are held in place by springs to ensure instantaneous engagement when the direction of rotation changes, though some specific high-speed clutches use centrifugal force to pull them away.

Sprag clutches operate based on your specific application and type:

1. Constant Contact Sprag Clutches (Most Common)
  • How They Work: Sprags are individually energized by ribbon or garter springs so that their curved lobes are always touching both the inner and outer rotating races.
  • Why it matters: Constant contact ensures there is zero "lost motion" or lag. When the races attempt to rotate in the opposite direction, the sprags immediately bind and transmit torque.
  • Risks: If constant contact isn't maintained, some sprags might catch before others during a direction change, resulting in uneven torque distribution and potential permanent damage to the ⁠sprag clutch springs.
2. Centrifugal "Lift-Off" Clutches
  • How They Work: Certain specialized, high-speed ⁠overrunning clutches use a centrifugal throwout design. When spinning at a very high overrunning speed, the centrifugal force of the sprag's mass overcomes the spring pressure.
  • The Result: The sprags physically lift off the race, eliminating all rubbing contact, which significantly extends the wear life of the internal components.
  • Limitations: These clutches have a minimum "lift-off speed." The drive mechanism must ensure the speed stays below this threshold during the torque-transmitting phase to allow the sprags to properly re-engage.
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Morning Dennis
Read the above. Not AI generated and counting the listed types of sprags the disengaging type outnumber the engaging types almost two to one
 
dobba99 said:
Interesting, around 52 seconds in you can just see the transfer gear rotate slightly as the heel dragging sprag exerts its influence. Check the bearings either side of the sprag, flick one (or both) of the rubber shields out and check that the grease hasn't got dried out, heel dragging equals heat generated.
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You may be onto something?
CNW e start conversion, sprag failures
 
Thanks. This is a lot of learning for me.
And I do agree AI results should be questioned!
Before this thread started, I did not even think about whether dog bones contacted or not and the pluses and minuses of that!
Now I have learned that they actually design sprags for disengagement or permanent dog bone touching.
Dennis
 
Interesting stuff. I've dealt with a lot of sprag clutches on automatic transmissions but never knew they were used in applications where there was no active lubrication. Also, in looking at the pics, the sprag in question seems to have a constantly "sliding" surface which seems to be very poor choice for something that is rotating at a rather high speed. Sprags in automatic transmissions essentially never wear out but, of course, they are of a different design and submerged in oil. I can see a sprag of the type in question used for a low speed/greased application...
 
dobba99 said:
Is that rust? or whats left of baked on lube? how do the bearings feel? rough? or smooth out when oiled?
If they feel ok repack with a high temperature grease loaded with molybdenum disulphide.
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No rust just dryish grease. Nice n smooth but I’ll clean and repack, thanks for the advice.
 
YING said:
Cafe,
Does the rubber boot go back in place correctly on those sealed bearings or am I missing something?
Thanks,Mike
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It’s actually hard plastic not rubber with a central groove on the inner side roughly 3/4 of its width to allow for the races. They simply snap back in place as they have a small lip on both inner & outer edges.

The second bearing was interesting. There was no sign of grease at all, everything nice n shiny, wasn’t expecting that.

As it may take a while to get a box of goodies from Matt including a sprag I might be tempted to replace the old one with the refurbished bearings and give it a go. I’m such a friggin’ expert in stripping & rebuilding the primary I did it in less than 1 hr heck I might even try it blindfolded like soldiers do with their rifles 🤣🤣🤣
 
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Café au Lait said:
It’s actually hard plastic not rubber with a central groove on the inner side roughly 3/4 of its width to allow for the races. They simply snap back in place as they have a small lip on both inner & outer edges.

The second bearing was interesting. There was no sign of grease at all, everything nice n shiny, wasn’t expecting that.

As it may take a while to get a box of goodies from Matt including a sprag I might be tempted to replace the old one with the refurbished bearings and give it a go. I’m such a friggin’ expert in stripping & rebuilding the primary I did it in less than 1 hr heck I might even try it blindfolded like soldiers do with their rifles 🤣🤣🤣
Click to expand...
Cafe,
I appreciate you getting back with me.As for myself,the Estart system is a lifesaver being I don’t weigh enough to get a good kick. I have been watching all these replies but still think Matt’s kit is far and away the best. The next time I have it apart I will inspect those bearings to see how they look.Do you think they have something to do with the sprags life?
Thanks again,
Mike
 
YING said:
Cafe,
I appreciate you getting back with me.As for myself,the Estart system is a lifesaver being I don’t weigh enough to get a good kick. I have been watching all these replies but still think Matt’s kit is far and away the best. The next time I have it apart I will inspect those bearings to see how they look.Do you think they have something to do with the sprags life?
Thanks again,
Mike
Click to expand...
Honestly I don’t think I’m qualified enough to comment but logic tells me they shouldn’t be dry at least.

I’m happy to stick with Matt’s design (why wouldn’t I?) but I do need a definitive answer as to lubrication if at all. Inside the sprocket housing it was a fair bit messier that last time I removed it meaning grease or oil and presumably belt dust combined. I’ll probably take the main sprocket off and check the crank seal.
 
dobba99 said:
Is that rust? or whats left of baked on lube? how do the bearings feel? rough? or smooth out when oiled?
If they feel ok repack with a high temperature grease loaded with molybdenum disulphide.
Click to expand...
@YING - A quote from an email from Cross+Morse: In [this] case the sprag will require lubrication as the crankshaft will be rotating continuously.

Ideally the sprag will be lubricated by oil (Type A automatic transmission fluid), if not you can use grease, we recommend Kluber Polylub WH2. For either option it is imperative to ensure the lubricant is not an E.P. (extreme pressure) type, or contain any additives such as molybdenum disulphide, graphite and P.T.F.E.
 
gortnipper said:
@YING - A quote from an email from Cross+Morse: In [this] case the sprag will require lubrication as the crankshaft will be rotating continuously.

Ideally the sprag will be lubricated by oil (Type A automatic transmission fluid), if not you can use grease, we recommend Kluber Polylub WH2. For either option it is imperative to ensure the lubricant is not an E.P. (extreme pressure) type, or contain any additives such as molybdenum disulphide, graphite and P.T.F.E.
Click to expand...
...although, the bearing they're talking about above is not the sprag
 
Café au Lait said:
It’s actually hard plastic not rubber with a central groove on the inner side roughly 3/4 of its width to allow for the races. They simply snap back in place as they have a small lip on both inner & outer edges.

The second bearing was interesting. There was no sign of grease at all, everything nice n shiny, wasn’t expecting that.

As it may take a while to get a box of goodies from Matt including a sprag I might be tempted to replace the old one with the refurbished bearings and give it a go. I’m such a friggin’ expert in stripping & rebuilding the primary I did it in less than 1 hr heck I might even try it blindfolded like soldiers do with their rifles 🤣🤣🤣
Click to expand...
Jeez - those bearings have got me more worried than the sprag! I can live without an e-boot but not with that noise (or potential for further damage).
I might pull mine out to check.
Cheers
 
robs ss said:
Jeez - those bearings have got me more worried than the sprag! I can live without an e-boot but not with that noise (or potential for further damage).
I might pull mine out to check.
Cheers
Click to expand...
Those bearings only come into play when the starter button is pressed. Cafes noise was the sprag.

Another thing I don’t hear folk talking about is how often they change the belt?

I’m thinking that we should be going in there every 10k or so to change the sprag and re grease the sealed bearings. When should we change the belt, every 2nd or 3rd such service ?
 
Fast Eddie said:
Those bearings only come into play when the starter button is pressed. Cafes noise was the sprag.

Another thing I don’t hear folk talking about is how often they change the belt?

I’m thinking that we should be going in there every 10k or so to change the sprag and re grease the sealed bearings. When should we change the belt, every 2nd or 3rd such service ?
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Morning Nigel
Those bearings are in play all the time the engine is running. The outer race (drive gear) revolves when the button is pushed but the inner race is on the engine sprocket.
All of this has a parallel with the fiasco of the first commando electric start mechanism. Back in the early 70s the factory designed an electric start that drove through the timing side (some of the 750 commandos still have the aperture for this) This nearly made it into production, but it had a design fault that destroyed the timing side case. The road testers at the time knew this and had to prove it to the management (they didn't believe it).
I wonder how many test miles/starts were done on all the kits now available? The factory road testers at the time were doing hundreds of miles a day. Test mileages like that would have shown up faults in the Cnw and Alton kits in very short order.
 
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dobba99 said:
Morning Nigel
Those bearings are in play all the time the engine is running. The outer race (drive gear) revolves when the button is pushed but the inner race is on the engine sprocket.
All of this has a parallel with the fiasco of the first commando electric start mechanism. Back in the early 70s the factory designed an electric start that drove through the timing side (some of the 750 commandos still have the aperture for this) This nearly made it into production, but it had a design fault that destroyed the timing side case. The road testers at the time knew this and had to prove it to the management (they didn't believe it).
I wonder how many test miles/starts were done on all the kits now available? The factory road testers at the time were doing hundreds of miles a day. Test mileages like that would have shown up faults in the Cnw and Alton kits in very short order.
Click to expand...
At the risk of tempting fate - 18,000 miles, six years and counting. So maybe it's not as doomy and gloomy as you're portraying.
And Nigel's service schedule has some merit!
 
robs ss said:
At the risk of tempting fate - 18,000 miles, six years and counting. So maybe it's not as doomy and gloomy as you're portraying.
And Nigel's service schedule has some merit!
Click to expand...
Agreed, once a problem is identified it can be dealt with.
 
Fast Eddie said:
Those bearings only come into play when the starter button is pressed. Cafes noise was the sprag.

Another thing I don’t hear folk talking about is how often they change the belt?

I’m thinking that we should be going in there every 10k or so to change the sprag and re grease the sealed bearings. When should we change the belt, every 2nd or 3rd such service ?
Click to expand...
Nigel,
I don’t understand your questioning about the belt. I have never even had to adjust mine since initial installation but I don’t bang shifts.What am I looking for?Excess dust? I know you are much more experienced on this and would like to know your thoughts.
Thanks,Mike
 

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