E-start engine sprocket 'sleeved' - as printed in Roadholder

Sorry that you have waited so long for a reply to this Martin, but I am possibly the best informed to give you a response as I got Ken Merricks, the author, to write that article. It is unlikely that Ken sees this forum.

I met Ken around four years ago and we chatted Mk3 starters (as you do of course when you first meet someone). I appreciated that he was a very thoughtful engineer and in my view he had most likely solved the sprag clutch 'flip over' under backfire. I had destroyed two sprag clutches in my time, every backfire initiated by a low battery voltage. Of course, the anti-backfire device should slip before the sprag reverses but it seems not to.

Ken's article describes very well all the factors involved in starter performance, and the key solution of reducing the gap between sprocket and gear to absolutely prevent the sprag from 'flipping' over centre.

What Ken does not define is by precisely how much he has reduced the gap, but he gives the information by stating that the outside diameter has increased by 0.010" and the inside diameter has been increased to 45mm.

If you take the parts (any previously damaged parts to save the expense of new items) to any competent small engineering company with rotary grinding equipment they will be able to reface the two parts and bond in a hardened sleeve. The actual sprags should be alright to reuse.

You must also up-rate the starter, solenoid, cables and battery. You need to lose the airbox and rotate the battery 90 degrees to fit a bigger one. The Oddesy PC680 is very good as it delivers 680 amps and loses virtually no charge on storage. I have not done Ken's modification myself as paying attention to avoiding backfires, and carefully resetting the anti-backfire device torque, has avoided any further sprag destruction so far. I use my starter most every time, perhaps 20 times a day for 20 outings last year?

Regards

Norm

Can anyone advise which edition of Roadholder this was - I do not recall it. ?

Thanks.

Alan

If the system allows it, here is a paste of Ken's Article!

COMMANDO MK3

ELECTRIC STARTER

BY KEN MERRICKS

I bought my Commando in 2004 from a work colleague, it came with a plastic bag full of bits for the electric starter, including a dismantled motor. Like so many others, the electric start had been removed because it didnât work.

The bike itself was great but I always had a job kicking it up and one day the kick-start stopped dead after the first compression whilst I was still going down, result I ended up in the Royal Infirmary and for 6 weeks thereafter hobbling around unable to walk, let alone kick up a 9:1 compression big twin.

I vowed there and then that if I could not sort out the electric starter I would be forced to sell the bike, so I set to and this is the story of how I did it.

The starter motor is an American design made by PRESTOLITE (press to light) forgive the pun, and was originally used on JOHNSON/EVENRUDE outboard motors. This motor, with mods, can be made to work satisfactorily by converting the original 2 brush set up to 4 brush thus increasing the starting torque. The 4 brush kit is available from NORVIL for about £50.00. The bronze bearings and oil seals were also replaced and at the same time the commutator was skimmed on the lathe.

Fitting the 4 brush kit is a little tricky and some soldering is necessary but can be achieved with a little care by people like us.

The original electrical wiring fitted by Norton to the starter was far too lightweight for purpose and was replaced with heavy-duty car type wire from the battery to the solenoid then on to the starter motor, including the earth lead to the engine. The solenoid was also replaced because it drew far too much battery current in operation. A Leyland Mini solenoid fitted in the available space, and drew less than half the current of the original.

Speaking of amps, I soon realised the original battery was not man enough and replaced it with a BMW Varta type 530 030 030 as fitted to the 1200cc boxer twin. This battery is 30ah with 300amp cranking current and will just fit between the frame down tubes. It does mean modifying the battery tray by flattening the tray and fabricating a new end flange bracket, giving a longer platform. So provided you make all of the mods you will have more than enough power to start your Commando first time every time, even in the depths of winter. Mine has been deliberately left out overnight in freezing conditions and it starts immediately.

There is, however, a further weakness in the starter system and that is the spragg clutch. This clever little device is a form of âfree wheelâ which engages the main shaft via a reduction gear drive from the starter motor. The sprag clutch transmits the drive to the main shaft when the starter button is pressed then free wheels once the engine fires up. Early sprag clutches had 14 sprags or teeth but later ones were increased to 18 to improve performance and reliability. In free wheel the sprags lean over to allow free rotation. When the starter is engaged, the sprags come up close to the vertical and carry the main shaft with them giving the required drive to the main shaft for starting. With use, the engine sprocket bore wears by engaging the sprags as does the gear which contacts the other end of the spragg allowing the sprags to go over centre and jamming the whole assembly, resulting in an expensive replacement sprag, sprocket and gear costing £200.00. If this happens, itâs no use replacing just the sprag, itâs necessary to replace all three items.

2

This happened on my bike and I was unable to turn the engine by any means. I managed to free it by dismantling the whole of the primary side and, upon examination, the I.D. of the engine sprocket and

the O.D. of the gear, engaging the sprag were damaged with grooves where the sprags had âdug inâ whilst going over centre. The sprag of course was completely wrecked. To avoid the expense of a new sprocket and gear I internally ground the sprocket diameter until the grooves had been removed, taking out 0.010â on diameter.

The gear was not so easy as it required an increase in diameter. I overcame the problem by selecting the outer hardened sleeve of a needle roller bearing measuring 42mm O.D. and 35mm I.D. from my local bearing supplier for £5.00 and by reducing the gear diameter fixed the sleeve with LOCTITE RETAINER. This involved reducing the hardened gear diameter by rough turning the diameter to give a clearance of 0.004â on diameter below the sleeve I.D. of 35mm. Rough turning is required to give the maximum âkeyâ and was easily achieved with a carbide tipped tool on the lathe.

The sleeve was grooved internally with a number of spiral grooves ground freehand with a âDREMALâ hand grinder to give a similar âkeyâ. The O.D. of the sleeve was then externally ground so that the ground diameter just entered the sprag and was free to rotate backwards but when rotated in the opposite direction, the assembly locked and drive to the main shaft would result.

Because the clearance between the sprocket and gear dia was reduced, the sprag angle was increased making it impossible for the sprag to travel over centre thus overcoming the previous disastrous jam up.

I have run this set up for the last 4 years and 5000 miles without a problem and although it all sounds a little complicated, it can easily be achieved with a little help from your local engineer and will save you a lot of money purchasing new.

If your bike is fitted with a belt drive you do need to fill the primary with oil to lubricate the sprag. If run without oil the life of the sprag will be reduced even if assembled with best quality grease. Belts are now available which will withstand running in oil, my own belt is over 4 years old and still o.k.

I run my bike on Castrol GTX 10-50 which does help the starter in cold weather. There are also alternative batteries available which do not require âtoping upâ which is a problem with the Varta, these are available from:-

Multi-Cell InternationalSwannington RoadBroughton AstleyLeicester, LE9 6TU

Motorworks LLPThe Old School HouseMeltham Mills RoadMelthamHolmfirth, HD9 4AT

Odyssey PC680 High Performance Battery 680ALow MaintenanceSame size as Varta

I hope these notes help you to get your electric start Commando to work reliably and extend your motor cycling to even older age. If you complete this work, your Commando will be capable of doing a 15 SECOND QUARTER on the Norton starter button!