The infamous sprag

There is a thread running on Access Norton, it suggests that the sprag runs on case hardened surfaces but the core material under the case hardening is too soft to support it properly, so the sprag can create bumps/depressions in the hardened surface which stop it working. The solution of these parts being made in a stiffer material and case hardened is being planned by CNW, hopefully these parts will be available in time for your repair.

Hi Mark,

You say:-

only to get 500yards before the sprag grabbed and spun the starter for all it was worth.

I have never heard of this happening before. The ONLY way I have ever heard a sprag failing is it going over centre as the bike starts when using the starter. Once it has started it should not be able to grab.

What ignition are you running ?

Standard points should not give a backfire when starting.

Boyer ignition (certainly the earlier ones) are known to give no spark at all or randomly advance or retard up to 30 degrees if the volts drop below 9.

I use Pazon and have not had any backfire issues. I am on my second sprag but original inner and out driving bits. Just under 70,000 miles since new.

Sprag was damaged and replaced when I had the Boyer.

Tony

Hi Mark,

Trust me get your electric starter working . My Mk111 just about tore my right foot off with a backfire. You need deep pockets to run these bikes, but in my eyes they are worth it.

GET IT WORKING

Andrew

The only way that the crank can grab the sprag is if the sprag is the wrong way round...that said, I took a hacksaw to mine - as a callow lad of 23 - after the starter pulled the hexagon from the nut on the anti-backfire clutch.

After more than thirty years of un-tutored and initially unbelievably ignorant tinkering with Commandos, I'm still not sure that it's possible to pay anyone to make one of the beasts reliable and keep it that way.

In my experience, it's a matter of perseverance and learning from mistakes. I don't mean this to sound rude or condescending but I'm really not sure if I could square the concepts of paying someone to work on something as straightforward as the primary drive with any expectation of a long and pleasant association with a Commando. Dirty hands and an increasing understanding of the beast are essential.

By the way, I think that you should name names. Was it a Commando specialist ?

'....so with the starter spinning with no effect...'

I know hindsight is always 20/20 but that alone should have raised alarm bells, no?

As for: '..a man whom is worshipped...' I'm with Richard on this one, names should be named.

A false prophet (and profit!) perhaps?

Mind you, is the sprag being run dry with a belt primary?

Mark, you'd have been quite justified in taking offence at my presumption. I'm afraid that the Talisker found me last night and I'm frequently something of a loud-mouth after a couple of glasses.

Having occasionally 'enjoyed' myself outdoors replacing hoses and cylinders on plant, I can quite understand why anyone who's done much of that loses any inclination to start again when they get home.

I'm still pretty sure that putting the clutch in with the sprags laying in the wrong direction is pretty much the only thing that could give the symptoms of no engagement when trying to start and then picking up as the motor ran.

It's certainly worth checking operation before replacing the cover.

Where did your fitter source his parts from ?

Previously Tony Ripley wrote:

Hi Mark,

You say:-

only to get 500yards before the sprag grabbed and spun the starter for all it was worth.

I have never heard of this happening before. The ONLY way I have ever heard a sprag failing is it going over centre as the bike starts when using the starter. Once it has started it should not be able to grab.

What ignition are you running ?

Standard points should not give a backfire when starting.

Boyer ignition (certainly the earlier ones) are known to give no spark at all or randomly advance or retard up to 30 degrees if the volts drop below 9.

I use Pazon and have not had any backfire issues. I am on my second sprag but original inner and out driving bits. Just under 70,000 miles since new.

Sprag was damaged and replaced when I had the Boyer.

Tony

Mark/Tony,

I have had bothfailures occur.

Once when exiting a motorway onto a roundabout, there was a judder and the engine stalled. On trying to re start I found that the starter motor was turning with the engine. We had to throw the bike on its side, to save the oil , remove the chain case and remove one of the starter gears. I put it in my pocket and continued riding for the rest of the weekend trip.

As someone else said the sprag wears little grouves in the inner gear and iteventually turns over, usually when starting the engine.

Subsequent to the above incident I had NW rebuild the entire thing. He said the only solution was to replace both inner and outer gear/sprocket and sprag. Expensive but it worked for about a year. Then after filling up one day at service station, I gaily pressed the button, as I had been doing for a year, and whiz bang crunch it failed again.

Not being too keen to be caught out AGAIN I have binned the lot and the bike now sports an entirely empty starter motor casing just for effect ! And it really annoys me when other Mk3 owners say, 'Oh mine's been OK for 40yrs.. Grrr.

After 30 years running my Mk 3 , both in Africa and UK , have always employed the following completelyreliable method for maintaining100% troublefree electric starter use : Install new starter motor , new spragand new battery -test bike starts with electric starter- thereafter continuestarting bikewith kickstart only ,neverusingelectric starter again.

Bike was run on standard points ignition until five years ago when Boyer was installed. Kickstarting has never been a problem with either ignition system -normally 2 or3 kicks with points / 1 or 2 kicks with Boyer.

The sprag going over-center is a (yet another) weak point. There is a solution that has been described before.

http://www.nortonownersclub.org/noc-chat/technical4-commando-forum/572586663?b_start=0#931771607

Norm.

Mark

The mk3 electric start mechanism can be made to be very reliable, see the attached link in Norman Lortons reply Or search on this site for the Ken Merrick mod.

If you are serious about wanting a reliable electric start for your mk3 this has to be done, just replacing parts will not cure the problem only delay another failure for a while.

The Ken Merrick mod details closing up the clearance so the sprag has no chance of 'flipping' and destroying itself.

Get that done, have your starter motor rebuilt with four poles & brushes, have the armature fitted with ball and needle roller bearings, fit heavy duty cables and a decent agm battery and you will have a starter motor that turns the engine over like a jap bike.

I did all this to my mk3 last year and I can honestly say I have not used the kickstart at all this year to start the engine even from a six month layup over winter.

I have done the 'ken merrick' mod for a member of the Yorkshire NOC and his mk3 wears a Maney big bore kit. That bike has one of the newer style of starters based on a hitachi motor, needless to say it starts very well.

If you want to bin your electric start mechanism you can chuck it my way, I will make it reliable.

Regards

Peter Shand

Well said Peter, I 100% agree; the irony being that I have yet to undertake the 'ken merrick modification' on my Mk3! There perhaps could be a definitive list in the technical section on this site regarding what needs to be done to fix the Mk3 starter system: ignition-battery-solenoid-cables-motor(options)-sprag. Currently, newbies have to research this forum and re-invent the wheel.

I would suspect the quality of some of the replacement sprag parts available if people are finding new assemblies failing quickly. The hardness of the sprocket inner and gear outer faces and underlying material is the issue, and material hardness is often expensive to ensure and difficult to qualify in a spare part.

It would be interesting if Andover Norton would consider making the parts to the 'ken merrick' dimensions and to their usual quality standards.

Norm

Previously norman_lorton wrote:

It would be interesting if Andover Norton would consider making the parts to the 'ken merrick' dimensions and to their usual quality standards.

Norm

Perhaps we should lobby them, no? Maybe if enough interested parties came forward it might become practical?

Previously peter_shand wrote:

I have done the 'ken merrick' mod for a member of the Yorkshire NOC and his mk3 wears a Maney big bore kit. That bike has one of the newer style of starters based on a hitachi motor, needless to say it starts very well.

If you want to bin your electric start mechanism you can chuck it my way, I will make it reliable.

Regards

Peter Shand

Peter,

Do you offer a service carrying out the 'Ken Merrick mods' to the sprag components for members? I am intending to re-install the e/s mechanism to my Mk3 (removed by previous owner) and modifying the parts on which the sprag operates seems essential. I would prefer to spend my money on a long-term fix than buy new parts throughout, only to have them fail in use.

Regards,

Allan.

Previously allan_walker wrote:

Previously peter_shand wrote:

I have done the 'ken merrick' mod for a member of the Yorkshire NOC and his mk3 wears a Maney big bore kit. That bike has one of the newer style of starters based on a hitachi motor, needless to say it starts very well.

If you want to bin your electric start mechanism you can chuck it my way, I will make it reliable.

Regards

Peter Shand

Peter,

Do you offer a service carrying out the 'Ken Merrick mods' to the sprag components for members? I am intending to re-install the e/s mechanism to my Mk3 (removed by previous owner) and modifying the parts on which the sprag operates seems essential. I would prefer to spend my money on a long-term fix than buy new parts throughout, only to have them fail in use.

Regards,

Allan.

Hello Allan

Yes I can modifiy your starter gear for you. Do you have a four pole four brush motor? If you are wanting your bike to still look original I can convert the old standard Prestolite two pole motor to four pole, four brush along with rolling element bearings (a ball race at the drive end and a needle roller at the non drive end.) This is depending on the starters condition.

I have also converted brand new harley davidson starters to fit the MK3 and that is the starter that i have fitted to my bike. (a brand new WPS starter for a harley is around £100)

PM me if you are interested

Regards

Peter Shand

Thanks Peter. PM sent (I think!)

Allan.

Sounds like an episode of 'The Sweeney'... no?