Author Topic: Can't get my magneto off - help!  (Read 1135 times)

Offline Simon59

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Re: Can't get my magneto off - help!
« Reply #15 on: 12.04. 2018 13:23 »
Thanks, I didn't think of using cold... I have access to some liquid nitrogen here at work, so I might be able to set up some kind of cold finger to cool the shaft and then apply some quick heat to the gear... This is all part of the fun of restoring an old bike of course! *smile*
Restoring a 1954 plunger framed A10 Golden Flash

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Re: Can't get my magneto off - help!
« Reply #16 on: 12.04. 2018 17:34 »
Don't want to flog a dead horse Bike Beesa, but I don't think it's quite fair to lay the problem at the door of morons using duff bolts. There actually is an inherent flaw.
Even fastidious owners can't tell in advance when the blessed thing is not going to extract the gear- whereupon the bolt can't be got out for examination or replacement. It only takes one very tight fitting taper to wreck the start of the lh thread, and then you're where Simon is. (Even when you have the unit off the machine and on the bench it isn't often that simple to get a damaged bolt out.)
I've got a few damaged ones lying around, which I keep as models for turning up replacements - so it's a problem I've seen a lot more of than I would ever have wished.

The principal of the auto-extract is perfectly fine, elegant and well- recognised, I completely agree. Excellent idea.  It's the detail execution of the particular item that isn't so fine or elegant. My own drives for attaching mags of varying diameters, tapers and threads to bench test equipment all self-extract - but they use proper internal shoulders. They are used a dozen times a day sometimes and they don't fail, even on the big tapers  found on a lot of 4 and 6 cyl mags. They all just need the one 3/8 BSF spanner from any ordinary toolkit, nothing fancy, same as an atd unit.

The number of times Simon's problem arises is too high, I think many would agree. My heart is always in my mouth when taking the things off machines, with that 'will it or won't it' worry. When it will, all well and good and then one can check the thing for condition, replace or whatever; when it won't, it can be a lot of time wasted. My point is not that the concept is bad, it isn't. But nothing will ever persuade me that is a respectable engineering approach to use the first turn of any thread as the load-bearer to get a tightly mating taper apart! 
Bill

Online RichardL

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Re: Can't get my magneto off - help!
« Reply #17 on: 13.04. 2018 23:03 »
Thanks, I didn't think of using cold... I have access to some liquid nitrogen here at work, so I might be able to set up some kind of cold finger to cool the shaft and then apply some quick heat to the gear... This is all part of the fun of restoring an old bike of course! *smile*

I have a feeling this is not the answer, but readily admit others here may know otherwise. What you have at the taper is two very similar metals (steels of likely similar composition) with near identical rates of thermal expansion and contraction. What you doeth to one you doeth to both. Now for my suggestion of how much force to apply................................................................................................... *dunno* *shh* *conf2* *pull hair out*

Richard L.
Plan on signing up for the world-wide 2017 DISTINGUISHED GENTLEMAN'S RIDE on September 30, 2018. Watch website at https://www.gentlemansride.com for details.

Offline BSA_54A10

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Re: Can't get my magneto off - help!
« Reply #18 on: 16.04. 2018 10:50 »
Don't want to flog a dead horse Bike Beesa, but I don't think it's quite fair to lay the problem at the door of morons using duff bolts. There actually is an inherent flaw.
Even fastidious owners can't tell in advance when the blessed thing is not going to extract the gear- whereupon the bolt can't be got out for examination or replacement. It only takes one very tight fitting taper to wreck the start of the lh thread, and then you're where Simon is. (Even when you have the unit off the machine and on the bench it isn't often that simple to get a damaged bolt out.)
I've got a few damaged ones lying around, which I keep as models for turning up replacements - so it's a problem I've seen a lot more of than I would ever have wished.

The principal of the auto-extract is perfectly fine, elegant and well- recognised, I completely agree. Excellent idea.  It's the detail execution of the particular item that isn't so fine or elegant. My own drives for attaching mags of varying diameters, tapers and threads to bench test equipment all self-extract - but they use proper internal shoulders. They are used a dozen times a day sometimes and they don't fail, even on the big tapers  found on a lot of 4 and 6 cyl mags. They all just need the one 3/8 BSF spanner from any ordinary toolkit, nothing fancy, same as an atd unit.

The number of times Simon's problem arises is too high, I think many would agree. My heart is always in my mouth when taking the things off machines, with that 'will it or won't it' worry. When it will, all well and good and then one can check the thing for condition, replace or whatever; when it won't, it can be a lot of time wasted. My point is not that the concept is bad, it isn't. But nothing will ever persuade me that is a respectable engineering approach to use the first turn of any thread as the load-bearer to get a tightly mating taper apart!

I can see where you and Simon are coming from, but if a part has worked fine for 60 years then there is not an inherit design flaw in it.
That does not mean that it could not have been done better, but it does mean it was done good enough for the purpose.
Design flaws are the problems you read about in the Agony Aunt columns of PERIOD PUBLICATIONS and the self extracting bolt never rate a mention in the magazines of the 50's 60's 70's & 80's.
It is a bit rude to criticise a design from the 50's 60 years latter when it was not a problem in the day.
Exactly the same applies to stiction between the slides & carb bodies and wet sumping.
None of these were a problem when the bikes were being used within their design parrameters.

I ran 2 A 10's in  very wild youth, one a fire breathing monster 11.5:1 running on a nitro benzene/ petrol mix and the other, a bog standard rat bike A 10 that I hoped would still be where I left it after lectures.
The only problems I had with the magnetos was ripping all the teeth of the drive gear on the Friday night drags along Friendship Rd Port Botany.
On both the bikes, pulling the magneto pinion was a weekly job so if I pulled one off I pulled a thousand off and never ever was there a problem.

Fast forward 30 years and every second idiot has got an impact driver 4 times the size of their IQ and they think it is perfectly fine to rattle a magneto onto a taper or smash it on with a 4lb hammer when all that is needed is a gentle squeeze, and this is where the rot sets in with tapers jambed on way too tight so naturally when some one tries to extract it it is beyond the shear strength of the threads and they strip.

We can do a lot of things a lot better now days and a lot cheaper to boot but remember BSA had to be competatively priced other wise they would have gone the way of Douglass, Vincient and all the other precision engineered motorcycles.
Bike Beesa
Trevor

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Re: Can't get my magneto off - help!
« Reply #19 on: 16.04. 2018 15:35 »
I see where you're coming from too, I really do.
And some have lasted a long time, I know.
And I also agree about people with rattle guns and lump hammers. Unwise.
But I still think using a turn of thread as a lever is a very bad idea and I'm surprised it got from drawing office to production without someone saying 'hang on a minute, this should be done differently'. I bet BSA wouldn't have done it themselves. Mostly, though, I think Lucas were very good at producing value-for-money things that worked as well as anyone could expect.
Vincent used the same sort of ATD almost from its invention, to help get round the inherent problem of an assymetric engine running on an ignition system designed for symmetry (but clockwise drive) - and I've seen first-hand a few of their ATD centre bolts go exactly the same way, without any obvious help from rattle guns and hammers! Velocettes too.
Anyway, they are what they are, and I recognise we have to live with them! I'm living with one on my A at the moment, and another on my 650SS Notrun, so I'm not so very one-eyed about it. I just wish they didn't die so (relatively) often, and weren't such sods to deal with when they do, is all!
And of course I wish the fibre teeth stayed on too - been there more than once over the years.
Bill

Offline BSA_54A10

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Re: Can't get my magneto off - help!
« Reply #20 on: 17.04. 2018 10:10 »
And there we will have to leave i Bill.
I am off now to pack the van for the run down to the All British
Annoy you all next week
Bike Beesa
Trevor