New Dvelopement MK3 Sprag not engaging

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hillbone

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HI .
Thanks for everyones help last week but nothing has changed, tried everything.........however I have noticed that I have a considerable air gap between the large inner washer (06-5828) that butts up to the Rotor and the crank gear (06-4731) when I tighten the outer nut up to 70lbs. In other words the crank gear is not hard against the washer and the washer is not hard against the Rotor.
I can actually turn the crank gear by hand if I twist it hard enough. The reason it doesn't butt up hard is because the race , inner (06-5820) is too long in length.
Should all these parts butt up hard against each other. In other words, the rotor would be firm against the washer and crank gear?
Happy Days???????
Cheers Hillbone
 
hillbone said:
.........however I have noticed that I have a considerable air gap between the large inner washer (06-5828) that butts up to the Rotor and the crank gear (06-4731) when I tighten the outer nut up to 70lbs. In other words the crank gear is not hard against the washer and the washer is not hard against the Rotor.
Click to expand...

There should be sufficient clearance for the 06-4731 crank gear to turn freely in the clockwise direction (if turned the opposite direction it should immediately be locked to the crank by the sprag) and the rotor should pull down hard against the 06-5828 washer when the rotor nut is tightened (see Mk3 manual Fig. C52(a).
http://britmoto.com/manuals/Manuals/850_man.pdf

hillbone said:
I can actually turn the crank gear by hand if I twist it hard enough.
Click to expand...

I assume you mean when it is disconnected from the rest of starter drive, in which case you should be able to turn it clockwise relatively easily.


hillbone said:
The reason it doesn't butt up hard is because the race, inner (06-5820) is too long in length.
Click to expand...

The crank gear shouldn't be "clamped" to the crank. The crank gear drives the crank through the sprag. Once the engine has started the sprag disconnects and the crank gear should then "freewheel" on the crank. If it did not, then the complete starter drive would be driven by the crankshaft resulting in its destruction.

06-5820 should be 1.040" (26.42mm) long.
 
Thanks. I'm clutching at straws here. We've been trying to figure out for weeks now why the assembly just spins and the sprag doesn't grab. It definitely does bite when you turn it by hand anti clockwise but when you hit the starter it just all spins.
New parts, upgraded starter motor, upgraded wiring, the lot.
Clueless still!
 
Check that your starter rotation is correct. If it is a Harley mod, it must be reversed from on a Harley.
Also, if you have the sprag on backwards it will only spin. Check both of these things.

Jaydee
 
My Prestolite starter was sent out for the 4 brush upgrade and works well and spins in the correct direction. Did not know that. Now use the D.D. starter motor to save weight and spin way faster.
 
jaydee75 said:
Check that your starter rotation is correct. If it is a Harley mod, it must be reversed from on a Harley.
Also, if you have the sprag on backwards it will only spin. Check both of these things.

Jaydee
Click to expand...



1. If he has my AGTS (not DD) starter it for SURE is a CW starter.
2. If he kick starts a MKIII with a reversed sprag, with one blip of the the throttle the starter will be spun up to 45,000 RPM. It WILL probably explode and (FWIW) I DO NOT warranty them.

3. A sprag that has been abused, unintelligently altered or damaged could possibly fail to engage due to the super thin sheet spring being damage and not causing the pre-engagement preload.

IMO - The sprag rotates with the engtine sprocket and lightly drags on the inner race due to the pre-engagment/synchronous engagement preload spring.(for lack of a better name)
 
Hello again.
I began a thread 2 weeks ago about this and I have covered all the above. It is the new silver starter. (forget the name) I bought it 5 years ago. Everything spins in the right direction. I am using new sprag, new sprag drive sprocket. Tried roughing up the surface. I am not using ATF. I have even removed the spark plugs ( to reduce compression), kicked the bike over and then hit the starter whilst there is momemtum and less load on the sprag and it still won't grab.
From stationary, the sprags grab when you twist it by hand in the anti clockwise position.
 
I re-read your first thread about this including my comment too. The other thought I had is the overload back-fire device. From experience, though I can't quite recall the exact symptom/sounds, a part of the device had failed. What I seem to remember was the big nut holding the thing together had failed in such a way as to allow the starter motor to turn, but since the back-fire device was not locked together because of the broken nut it just spun. I also seem to remember this was not accompanied with any racket that would usually be associated with a normally overloaded back-fire device. I think that nut broke in almost a perfect ring just under it's hex.
 
hillbone said:
I am using new sprag, new sprag drive sprocket.
Click to expand...

What about the engine sprocket?


Biscuit said:
The other thought I had is the overload back-fire device.
Click to expand...

Operating the starter with the primary cover removed should prove whether it's the overload backfire device or the sprag that's slipping.
 
I greased up a new sprag and it did not grab, got all the grease out , dried it up and it worked great, might want to check that.
 
I had this same issue a few years ago when i replaced my sprag.

I thought i could get away with ignoring the advice on the OldBrits web site:

"When replacing the sprag bearing, you need to make sure the bearing race in the drive sprocket and the bearing race on the crank gear are not worn and dimensionally correct. The drive sprocket (06-4681) I.D. should be 2.280" to 2.281" and the crank gear (06-4731) O.D. should be 1.6253" to 1.6248". The old sprag bearings came with 14 rollers, where the new ones come with 18 rollers and since the sprag bearing is normally a trouble spot with the starter system, it is recommended you upgrade to the new bearing if you have the old bearing."

After watching the new sprag spinning uselessly, I finally gave in (and after talking to Fred at OldBrits) and also replaced the drive sprocket and the crank gear as well.

After all, the sprag does its job by engaging the crank gear with it inner surface, and the drive sprocket with its outer surface. It must engage with both of these items in order to function.

Yes, it is an expensive proposition to replace all three parts, but it's now almost 10,000 miles later for me and my kick lever is still packed away in a box somewhere gathering dust.

The starter works perfectly every time.

Bite the bullet and replace all three items. At the very least, put a caliper on the crank gear and the drive sprocket to see if they are in spec. Mine were only off by a couple of thousands, but that was enough to make all the difference in the world.

Good luck.
 
Hey all,

While developing the cNw electric start conversion, it was our intention to also see what we could do to possibly better the MkIII starter set up to make it more reliable and better performing. We wanted to see if we could somehow incorporate what we learned from the new starter kit and make it a relatively easy retro fit. In other words, replacing as few parts as possible and not alter any of the major components

The first thing we determined was that the sprag clutch design is in fact pretty good and well built compared to others available. Interestingly enough, this sprag is being used in a number of demanding applications without any issues. It appears that the problems are associated when used in the 1975 electric start system

So the next step was to look closer at the other parts associated with the starter system. Having taken a lot of the MkIII primaries down, one thing that I have certainly noticed is the damage caused by the sprag engagement pins on the front sprocket surface and the crank gear surface. The surfaces become wavy and this will certainly be a hard surface for the sprag to grab onto since it may 'skip' as it's trying to get a bite and fully engage

When I went down to Special Tool Solutions (that are developing the cNw electric start conversion) John told me to bring some parts to do some testing. While there, we used a Rockwell tester and the case hardening on both the front sprocket and the crank gear was at 30-40 HRC (Rockwell C). It was determined that this case hardening was 0.030-0.040 deep. We then cut the part in half and tested them for hardness below the case hardening and found an extremely soft HRC of 10....or less. Almost down to the Rockwell B scale.

What this means is that even though there is a case hardening (and not very hard at that) the surface below it is extremely soft. In other words, it appears to give away when pressure is applied and literally 'dent' the surface. This uneven surface is then really hard for the sprag to get a positive engagement on

It seems that most of those that replace all of the parts associated with the starter system end up with a fully functioning and reliable set up. This for as long as the parts don't get compromised such as the 'denting' described above

When STS started the development of the new starter kit, material quality was on top of the list. It was decided to use an S7 tool steel for both the front sprocket and crank gear. This tool steel is extremely durable and strong measuring a HRC 60-62. While testing the starter system with 1000 plus starts to date, these surfaces are not showing any distortion or wear whatsoever. Is it overkill as far as material ?....maybe, but the bottom line is that it gets us piece of mind knowing that it will hold up over time

So what John at STS and I are thinking about at this time is to finish up the testing on the e-start and when we are confident that the complete kit is just right, move forward with developing an upgrade kit for the original MkIII system

This kit will tentatively consist of a front crank sprocket and crank gear both made out of S7 tool steel. It will also include a new sprag bearing, same design as the original but with 18 engagement pins instead of the 14 that was on the original sprag. So a very straight forward install

Stay tuned

Matt / Colorado Norton Works

www.coloradonortonworks.com
 
A U.S. Gentleman once said to me decades ago when he was developing his electric start system to go with his primary belt systems for Triumph and Norton twin motor cycles........' What the hell is wrong with using a Bendix...they have been used for many decade,they are reliable and anyone can fix them when they go wrong'.
One UK road test on a friends so equiped TR6 reported the dry running belt driven diaphragm spring clutch and starter system and I quote..... 'A REVELATION'.
Mind you anything would be a revelation compared to that lump Triumph called THE CLUTCH that suffered from slip, drag and heavy clutch lever action.......... and for those unaware of the qualities a motor cycle gearbox mounted clutch is SUPPOSSED to posses a few of the qualities are that it will......
1. NOT slip when fully engaged even when hot.
2. Free off INSTANTLY WITHOUT DRAG whenever required even when hot.
3. Possess the LIGHTEST rotating weight reasonably possible.
4. Be EASILY operated by the user at all times.

Not my idea but qualities listed by Mr Phil Irving MBE in his book 'Restoring and Tuning Classic Motor Cycles' which clearly the people responsible for that rediculous bronze plated lump NVT called a clutch fitted to late 750 and 820 Atlas Mk3s (Commandos)
 
Matt
It makes me happy when I read about your improvements as you work with.
The fact that you are now working on a project that aims to improve the existing start-system on our MK3 is really interesting . Continue....

Vidar
 
cNw said:
Hey all,

While developing the cNw electric start conversion, it was our intention to also see what we could do to possibly better the MkIII starter set up to make it more reliable and better performing. We wanted to see if we could somehow incorporate what we learned from the new starter kit and make it a relatively easy retro fit. In other words, replacing as few parts as possible and not alter any of the major components

The first thing we determined was that the sprag clutch design is in fact pretty good and well built compared to others available. Interestingly enough, this sprag is being used in a number of demanding applications without any issues. It appears that the problems are associated when used in the 1975 electric start system

So the next step was to look closer at the other parts associated with the starter system. Having taken a lot of the MkIII primaries down, one thing that I have certainly noticed is the damage caused by the sprag engagement pins on the front sprocket surface and the crank gear surface. The surfaces become wavy and this will certainly be a hard surface for the sprag to grab onto since it may 'skip' as it's trying to get a bite and fully engage

When I went down to Special Tool Solutions (that are developing the cNw electric start conversion) John told me to bring some parts to do some testing. While there, we used a Rockwell tester and the case hardening on both the front sprocket and the crank gear was at 30-40 HRC (Rockwell C). It was determined that this case hardening was 0.030-0.040 deep. We then cut the part in half and tested them for hardness below the case hardening and found an extremely soft HRC of 10....or less. Almost down to the Rockwell B scale.

What this means is that even though there is a case hardening (and not very hard at that) the surface below it is extremely soft. In other words, it appears to give away when pressure is applied and literally 'dent' the surface. This uneven surface is then really hard for the sprag to get a positive engagement on

It seems that most of those that replace all of the parts associated with the starter system end up with a fully functioning and reliable set up. This for as long as the parts don't get compromised such as the 'denting' described above

When STS started the development of the new starter kit, material quality was on top of the list. It was decided to use an S7 tool steel for both the front sprocket and crank gear. This tool steel is extremely durable and strong measuring a HRC 60-62. While testing the starter system with 1000 plus starts to date, these surfaces are not showing any distortion or wear whatsoever. Is it overkill as far as material ?....maybe, but the bottom line is that it gets us piece of mind knowing that it will hold up over time

So what John at STS and I are thinking about at this time is to finish up the testing on the e-start and when we are confident that the complete kit is just right, move forward with developing an upgrade kit for the original MkIII system

This kit will tentatively consist of a front crank sprocket and crank gear both made out of S7 tool steel. It will also include a new sprag bearing, same design as the original but with 18 engagement pins instead of the 14 that was on the original sprag. So a very straight forward install

Stay tuned

Matt / Colorado Norton Works

http://www.coloradonortonworks.com
Click to expand...


Sounds like you are on the right track with your MK3 ideas /findings Matt.
One other thought as to what causes some of the problems encountered with that system- I wonder how many of the problems are related to low battery start attempts?
Triumph had some problems with the sprags in their pre 1999 Daytonas and much of that was due to low battery start attempts. The Riders manual for my 05 warns against using the starter when the battery is anything but fully charged.
The sprags just don't bite properly.
It's a hard thing to protect against. One idea might be to incorporate sort of low voltage cutout switch that would not allow starter usage should resting battery voltage drop below a lower limit. The rider could still start the bike with the kick start when this occurs.
I'm also thinking about adding a tiny second battery which would be isolated from the main Electrics of the bike during starting. It would only supply power to the ignition and only for startup. Once started, a flick of a toggle switch would take the small battery out of isolation and put it in parallel with the bike's electrical system, so that it stays charged.

I have noticed that even with my Modern bike, starting from cold is near instant if the battery charger is left connected for the cold start, whereas considerable cranking is needed without the charger connected, even though the battery is new and fully charged. I believe this is because of the considerable voltage drop that occurs during starting. The ignition doesn't like the voltage drop, even though it still fires. Everything just works better if the voltage to the igntion stays high.

Glen
 
cNw said:
So what John at STS and I are thinking about at this time is to finish up the testing on the e-start and when we are confident that the complete kit is just right, move forward with developing an upgrade kit for the original MkIII system.
This kit will tentatively consist of a front crank sprocket and crank gear both made out of S7 tool steel. It will also include a new sprag bearing, same design as the original but with 18 engagement pins instead of the 14 that was on the original sprag. So a very straight forward install
Click to expand...

Hello Mike,

Great news and I salute your diligence. Count me in for these upgraded parts for the Mk3 starter mechanism.

-Knut
 
Count me in for this harder material sprocket (s) / improved sprague upgrade concept. Sorry but could not wait for the Pre MK111 starter and bought a MK111 as I needed to ride and as the years fly by I realize now-now is the way. :roll:
 
Matt,

As usual you are on top of things. We used S7 steel in machine tools and plastic molds in my engineering days. It is a good choice for the application.

Please keep us posted on the MKIII upgrade. Maybe start a progress thread once you start working on it.

Also put me on the list for the kit :D

Dennis
 
Hello all,

My '77 destroyed the sprag assembly last weekend.
Who sells a new reliable kit at present?
How far away is the cNw kit?
I need the sprag 06-4733, crank gear 06-4731, and engine sprocket 06-4681.
The sprag is smashed/cracked, both the crank gear and the engine sprocket are dented (as Matt says) so both need replacing.
Should I replace the needle roller bearing and the inner race also? they look ok. (60-4711 and 06-5820)

Regards
Graeme
 
the needle roller comes assembled within the gear, the inner race is to separate order IIRC.
The lip on the roller outer case forms a dam to retain lubricant for the rollers, mostly a good thing.
We have found S7 to be barely and in some cases unable to reach Rc 60. It often doesn't have the carbon necessary to completely form the carbides required to achieve that degree of hardness.
S5 on the other hand is more capable of Rc 60 even after a good tempering to convert RA.
The original items in the old girl I have are cased to Rc 60-62, they are dimpled from early spark issues caused by an old Boyer and feeble battery so the case is probably thin, nothing was sectioned and etched to measure depth.
It is nice to see CNW taking the lead and providing an option.
Any properly through hardened items can be more resistant to dimpling and that is a big plus. The extra couple of points in harness in the application is probably not relevant in terms of measurable life.
I have the exact mileage recorded when our sprag train was replaced with new A/N items, a new battery, #6 gage cables, and a Trispark. Function has been flawless. Still using the Prestolite 2 brush starter.
The new sprocket averaged Rc 62, the gear Rc 57. With the engine cold I do use the leg to help get the mass rotating as the button is applied. Once warmed it's the button only. I expect it to see me out.
In the past it was believed the old Boyer/battery was the culprit for the early spark issues and it was. The points and AAU worked flawlessy until one day some excess points cam lube migrated onto the front set of contacts and spark timing acted erratically similar to the Boyer. That was the reason for moving from points to the Trispark.
Tomorrow is supposedly going to see a high of 61°F and it will be the last run for the season.
Extending a Happy Thanksgiving to those who celebrate it, condolences to those who don't.
All the Best.
 
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