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[Les H]

Thanks for the info Mark, now I know for sure I'm in for a real struggle.

Thanks also Vince, surprisingly so far I haven't put the nut back on to extend the reach of my puller...a good idea...I'll give it a go, its worth a try. If it still doesn't work with my existing pullers, I'm going to wait for another puller I've just ordered from Hong Kong....it has 2x tie bolts across the legs (diameter wise) which hopefully will stop them splaying outwards and slipping off the sprocket which always happens when the pressure is increased...Will come back with any results if successful on any attempts... Thanks again....Les

[Les H]

Oh it just occurred to me I could have got myself a large Jubilee clip and had this around and clamping the legs together....I know I don't have one that big to hand but will try to get one locally (I'm in the sticks so don't have that type of shop locally)....CU later

[Les H]

LATEST UPDATE:....I found some spare time to return to the garage to get that mag sprocket off (duplex type)....Made up a really tough puller fitted a Jubilee clip around the legs to stop them splaying out sideways, tightened the bolt slowly...no joy...applied more pressure and struck the extractor bolt with hammer to shock the pulley loose...no movement....then carried on exerting massive spanner force then click....the teeth broke off the sprocket!


Incredible! the force I was exerting was enough to pull of the main engine crankshaft drive sprocket but the mag shaft is only about 10mm diameter yet the sprocket is absolutely fused onto the sprocket. I can only assume something Like Loctite bearing retainer has been used to hold the thing to stop slippage. This difficulty seems not to be a one off though as I read in a "Classic Bike " mag of 1992 that the bike before restoration had had the mag crankcase extension snapped off by a previous owner in their attempt to remove the sprocket and when on the bench a professional team of mechanics nearly broke their heavy-weight extractor before finally managing to remove the sprocket.

[Les H]

CORRECTION..."the sprocket appears to be fused onto the magneto shaft......etc. etc.

[Bullet Whisperer]

Hi Les, I would be looking at setting a puller up, with a good amount of 'pull' wound on to the sprocket. Don't mess about with a blowlamp, heat gun or whatever - you need a propane / oxy torch going pretty fiercely and apply the very hot flame near the centre of the sprocket, making sure you get lots of heat in VERY quickly - you want the sprocket boss to expand before the heat gets to the magneto shaft. It is surprising how many things I have shifted like this and obviously, if a first attempt fails, let it all cool right down before having another go. I am sure this method should work for you. Very hot and very quick are the key points with this method, as I am sure you will understand. Regards, Paul.

[Les H]

Thanks Paul...yes I could try again and as you suggest wind on a big force with the extractor and THEN heat near the centre of the sprocket but away from the shaft....The only torch I have is a good quality plumbers torch that uses MAP gas it is pretty fierce so will try that....Ideally a small oxy acetylene flame would localise the heating better and keep it away from the shaft....will try this method though....otherwise it's a sprocket chopping job....will get back to let you know whatever happens....don't hold your breath....dead busy on other jobs at the moment....ATB....Les

[Les H]

Latest Update No2: Well I managed to find some time to try again....Carried out the last suggestion of fitting the puller and heating the sprocket with a torch....Biggest problem is the lack of room around the puller legs to heat the sprocket sufficiently with a plumbers gas torch but tried anyway only to shear more teeth of the sprocket so this wasn't going to work.


So bought a small quality angle grinder and some 0.8mm metal cutting discs, refitted the duplex chain with the old ground off link so it couldn't turn and then used the grinder to cut off the toothed section. This worrying method actually worked pretty quickly and with the sprocket that much smaller, I could unbolt the mag and the remains of the sprocket went through the crankcase hole to release the mag. The joy soon disappeared when I remembered I still needed to get the sprocket remains of the mag spindle.....At least I could now get at it more easily heat it far hotter then clamped the sprocket as tight as I could in a vice and used a pointed drift on the spindle end and hammered it hard as I dared hoping the would dislodge it and knock it through.....Nope, it still on and I'm concerned the spindle is showing slight signs of being distorted or bent....truly unbelievable...it just does not make sense....surely these sprockets are fitted onto a plain taper? but you could imagine the sprocket was screwed on, even welded!


Phoned West Somerset railways renovation workshop to see if they could help using Oxy Acetylene and a massive press....trouble is I reckon I will have to weld on a thick metal ring on the sprocket remains to increase its size to enable it to be held or braced against the pressure of the press....Not hopeful....reckon I'm going to need a new armature for the mag. Does anyone know if I can buy a new (pattern) replacement?...Cheers... will update again sometime....Les

[Dennis C]

Hi Les, If you do damage the shaft Armoto in Chesterfield will fit a new shaft to your existing armature, only thing with them is if you need a rewind specify they must do it to original spec, Ie 47k secondary, they did two for me a couple of years ago which were only wound to 28k, to save money I guess, I returned them both to be done again which they then did correctly.

[Mark M]

Les, sorry to hear it's turning into such a trial. If you've got the mag off leave it alone and send it to Dave Fisher (Moathouse Magnetos) and let him decide how to proceed. He can supply a new correct armature as he (well his wife!) winds them. I use him for all my mag jobs, he is excellent. If you can't find the number through Google come back and I'll find it for you.

REgards, Mark

[Les H]

Hi Dennis and Mark, thanks so very much for getting back on my problem....before I come back on your suggestions I have some good news...well it's good news for me....I eventually got the sprocket off....two hours later I'm still finding it hard to believe I managed it, I'm mentally and physically drained. Before taking it to the railway workshop I noticed there was a small gap behind the sprocket remains that just left room to get something behind it for the puller, so made several different forms of puller legs but no luck then remembered I had one of those massive split disc pullers where two halves of the discs are clamped behind the item to be pulled off by a heavyweight two legged puller....anyway I tried this and even this massive device started to bend...but I again tried with additionally heating it with the blowlamp as Paul had suggested and hammered on the centre bolt over and over again....I repeated this process three times and bang eventually the sprocket jumped off....absolutely fantastic.


Anyway....I've stripped the mag down....but now I've got another problem it seems....the magneto tapered drive shaft has come away from the magneto! It's on a tiny spline set in the front brass section of the armature with a very small diameter brass shaft which appears to have snapped. I've never seen this happen before but now I DO need a new shaft or the brass part that joins it together. Have phoned both Armoto and Dave Fisher and had to leave a message so probably they will phone back next Monday onwards so until then I don't know where I will be sending the armature too but will post again here when more info available....many thanks again guys.


PS....DENNIS...regarding the secondary winding resistance I'm interested in discussing this topic if possible with you but will post this as another new and separate topic when I have recovered a bit more....much appreciate if you wouldn't mind sharing some info on this.....best regards again to you both......Les