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Mk.lla crank bodge?

Submitted by michael_wattles on Sat, 12/03/2016
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Commando
There is no rotor keyway on my 1974 Interpol (decommissioned) commando, a December '74 reg. i.e. very nearly a '75. This may be more than coincidence (or wishful thinking..) I understand a mk3 crankshaft is elongated on the DS but still had a rotor key and shouldn't fit the mk2a crank case anyway. Is my crank simply a bodge or possibly something of more interest from the factory changing from one model to another? Perhaps a Friday afternoon job, in late December, as it were.This crank has the threaded with the keyway cut into it, not on the shaft (which seems pointless). The rotor nut bore is larger than standard (but it still fits into the rotor) i.e. a '74/75 nut won't fit on the thread. The alternator is an RM23 and the (un-keyed) rotor has several extra shims to align with the stator. Consequently the rotor has fouled the primary chain case where the timing scale was located and the rotor nut has also made light contact.The bike was running without a rotor key when I bought it which doesn't seem unreasonable on the face of it and not ideal. Can I avoid major expense?

Submitted by john_holmes on Sun, 13/03/2016

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Sounds like a Fiday special, payday was Thursday in the Midlands so Thursday night was busy in the local pubs and plenty of sore heads on Friday morning. A fix on the B25 which had soft mainshafts and wore out keyways was to use the sprocket pulling holes to locate and drive the rotor. They are threaded and you can screw posts into them and drill 2 matching holes in back of rotor.

Submitted by robert_tuck on Sun, 13/03/2016

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going back many years it was common for alternator rotors to disintegrate. I remember seeing an article detailing how to positively fix a rotor to the sprocket so that the innefectual key arrangement was redundant and a loose rotor center irrelevant. This was all doable without an engine strip. Just involved some machining and a special star washer from the suspension of an obscure Italian scooter?, all done in some back street Italian workshop and on a Commando. It was a very elegant solution and should have been done by the Brit bike industry.

Submitted by michael_wattles on Sun, 13/03/2016

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Previously john_holmes wrote:

Sounds like a Fiday special, payday was Thursday in the Midlands so Thursday night was busy in the local pubs and plenty of sore heads on Friday morning. A fix on the B25 which had soft mainshafts and wore out keyways was to use the sprocket pulling holes to locate and drive the rotor. They are threaded and you can screw posts into them and drill 2 matching holes in back of rotor.

Thanks John foryour reply.Often said it thatThursday night'sthe new Friday!Myproject is a first for several decades and a bit in at the deep end, as the bike now lives outside. The omission of a keyway appears obvious but may have a history. I like the idea of developing an alternative setup now! Perhaps starting with a new rotor and sprocket and using a machine shop I have been recommended. Mike

Attachments ds-crank-no-keyway-on-shaft-jpg

Submitted by michael_wattles on Sun, 13/03/2016

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Previously robert_tuck wrote:

going back many years it was common for alternator rotors to disintegrate. I remember seeing an article detailing how to positively fix a rotor to the sprocket so that the innefectual key arrangement was redundant and a loose rotor center irrelevant. This was all doable without an engine strip. Just involved some machining and a special star washer from the suspension of an obscure Italian scooter?, all done in some back street Italian workshop and on a Commando. It was a very elegant solution and should have been done by the Brit bike industry.

Thanks Robert for your reply. I have attached some photos. An odd feature is the alignment of the stator and rotor with only the normal spacer and two shims.

I plan to bolt up the rotor with the sprocket, poss. alignedwith new pegs (screwed into the sprocket) and slid into new holes in the back of the rotor?! The correct spacing is not evident but I could take down the half inch spacers on the stator studs. Mike

Attachments stator-wo-xtra-shims-jpg

Submitted by robert_tuck on Mon, 14/03/2016

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Thats odd!,perhaps you have an earlier crank from an Atlas or similar ,certainly does not look viable as it is. I presume you have checked the chain run is straight. The Italian job also involved machining a pair of matching small tapers to ensure concentricity.

Submitted by michael_wattles on Wed, 16/03/2016

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I had anticipated this but I have decided to send the bottom end to be looked at. A part of my problem was not having anywhere to strip down the engine. I have bought the special tools for engine removal and the DS.After reading many interesting posts, I may try fitting a vernier sprocket and blue printing TDC and timing as a project with the engine out.I rebooted the refurb (excluding engine) after several years and a house move, changing the Boyer to points in Feb. and thinking of finally starting the bike again?! (As a teenage bodger, starting an Enfield nearly broke my ankle and I had heard about the low voltage Boyer issue. I fondly remember fettling points and have even reverted to vinyl over cd's for a similar reason.)I have spent far too long avoiding the engine and it may take one to know one but a bodge is a bodge.. is a bodge.Thanks for your help and expect an update this summer. Mike

Submitted by robert_tuck on Wed, 16/03/2016

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It may be an illusion but the rotor nut does not appear to have enough crank to fit to. The stator may also be something not normally fitted to a Commando. It will all become clear in the end. If not, then its not the end !!.

Submitted by michael_wattles on Wed, 16/03/2016

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Previously robert_tuck wrote:

It may be an illusion but the rotor nut does not appear to have enough crank to fit to. The stator may also be something not normally fitted to a Commando. It will all become clear in the end. If not, then its not the end !!.

Sorry! Did I mention I am a bit dyslexic? To end at the beginning then.. I have attached the as found pic - with the nut tightened up (and about 3mm of extra spacers) which just touched the inside of thecrankcase enough to mark it. (I had problems attaching more than one image. Dohh!)

And so it is the end that is the problem, or not the right end at least (by a few mm).

And of course, it's not arriving at your destination but enjoying the ride!

Attachments stator-as-found-jpg

Submitted by robert_tuck on Thu, 24/03/2016

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If you can find a copy of Classic Mechanics No1 Autumn 83 you will find an article by Roy Creasey dealing with this problem with insecure alternator .

 


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