Author Topic: magneto  (Read 1250 times)

Online RDfella

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Re: magneto
« Reply #15 on: 17.04. 2019 12:59 »
Was wondering the same, John, but the end casing has a register where it mounts on the magneto housing, so presumably everything is concentric. Also, the points gap difference, whilst not optimal, shouldn't make that much difference as by that time the spark has long gone (it's the ramp that counts). I intend putting the ring in a chuck with degree disk & dial gauge to get some readings.
Thinking further ahead, I presume these cam rings can be reground (apparently 60 deg rings are rather rare). Don't fancy doing that myself as I don't have an internal cylindrical grinder. It would need a good cam ring for me to copy on the pantograph. Don't fancy making one either for same reasons. I'd need to fabricate in the soft and then harden - after which of course it is likely to be considerably out of shape. Really needs grinding after heat treatment.
Another possible avenue is my fallback plan B. I've got a BSA?  twin distributor I could modify to fit. But then I'd have to make a new cam which, however, would be a lot easier than making a cam ring. Easy to do on a pantograph from a template, or in my jig-borer with a dividing head. Only issue then would be is the rotor brass long enough to contact the 2nd terminal in the cap?

Why is it that what should be simple turns out to be the most frustrating and difficult? Making the crank, timing gears, cyl barrels etc was relatively easy. Hardest part until now was making the head gaskets (couldn't get the right material). Now it seems the ignition is going to surpass the head gasket nightmare.
'49 B31, '49 M21, '53 DOT, '58 Flash, '00 Firestorm, Weslake sprint bike.

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Re: magneto
« Reply #16 on: 17.04. 2019 18:36 »
John - you could be right. Today I measured the cam ring. The ramp is .045 / .047 and measuring timing at .012 before top of ramps it comes out within a degree of 150/210. Pehaps I should make new crankcases and move the front cylinder to match the mag *????* *smile*
'49 B31, '49 M21, '53 DOT, '58 Flash, '00 Firestorm, Weslake sprint bike.

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Re: magneto
« Reply #17 on: 17.04. 2019 22:29 »
 Hi RD,
60 degree mags would be fairly rare , The only British V twins I can think of that were 60 degrees were Blackburne and Anzani  *????*
Presently I have a rather nice  V twin "special" to recomission, It has a very nice AJS 1000cc V twin engine housed in a rigid Norton frame
The builder provided the sparks by fitting two sets of points and coils so its set up like two singles, one ignition cam and the points mounted to suit the firing angle.
A few year ago I was sorting a Vincent twin that had distributer ignition, if a motorcycle size coil was used it would only run on one cylinder at tickover, stutter ,bang and chime in on number 2 as the revs rose, it would run OK on a big car size coil, but theres nowhere to hide one on a naked bike  *sad2*
I got a twin output coil and did away with the rotor and dizzy cap, runs like a champ since *smile*

So it might be possible to fit two sets of points to your distributer and grind off one side of the ignition cam  *????*

Going off on a tangent here, and more cost  *eek*
A flange mount manual BTH (original) as used on Tri**ph twins would be a better built instrument than the Lucas
and "should" work with a modified cam ring
The bother with them is the leads come out at the drive end, needing more space around the area
I have one fitted to my Super Rocket but it took some machining to get it fitted to the BSA
https://www.a7a10.net/forum/index.php?topic=1385.msg9873#msg9873
Well worthwhile though (in my opinion)

Another thought would be to modify an electronic pickup plate and run EI ???

John
1961 Super Rocket
1963 RGS (ongoing)

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Re: magneto
« Reply #18 on: 18.04. 2019 14:40 »

60 degree mags would be fairly rare

For darn good reasons John, as RD is finding!
Most of the V mags I see are 50° or 45°. 60° is  at the outer limit - but it should work for all that. However, your other options may well be worth considering - and all the more so if we're talking high compression??

Some of the (much) older twin mags used two separate detachable lobes inside the ring housings. Often, the lobes can be moved to go where they are needed with a bit of measuring drilling and tapping. But the open/closed circuit ratio is often way off what is ideal (too much dwell), so probably not a good plan here.

Modding a BTH would be an interesting exercise. Yes, they are very nicely made in all departments (a lot of Bosch thinking in them to be fair), but the pick-up arrangement of the KC2 is a PITA for a lot of engines. Their spark performance isn't markedly better than a K2F at low speed, but they hardly ever have firing interval trouble, their contact breakers hang together very well and you can mix and match parts in a way you wouldn't want to think about with Lucas sometimes! Probably be a serious one-off job to get a 60° ring made though  . . . .

Another left-field thought would be to modify a static coil magneto like SR2 - or better, a Joe Hunt. That would be 'just' a cam job for you RD in theory, like doing a dizzy. Both can be had with flange mounts, witness SR2s on Oilfied twins and Hunts on all sorts. The Hunt red competition spec twin-spark coil is a pretty fearsome thing! They do 'em for HDs (which are I guess are all 45° but IKBA)  . . . so maybe  . . .????
Bill

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Re: magneto
« Reply #19 on: 18.04. 2019 20:51 »
Thanks Bill and John for well-thought out suggestions & ideas.
Have been kinda sidetracked today, so intend looking at this again on Friday.
Being this is a one-off engine I don’t want to get into it too much more at this stage so, whilst a BTH mag looks interesting (and should fit without too much bother) I don’t really want to go down that route until I know whether this engine is a runner. I have always run BTH on my race bikes and rarely had any issues with them.
I nearly finished this engine almost two decades ago, but since then it’s just been lying on the bench. I got back to it just before Christmas, and now I’m on the (hopefully) home run. Engine is installed in frame and once I’ve modified the oil tank to clear the rear carb, found a kickstart (and got some sparks) it’ll be time for the big test.
So what I’m hoping to do is improve the phasing of this mag enough (if I can) to try for a start. If all is OK, then I think the best option is to fit a distributor - my original plan B. I have a Lucas DKX2A – type RO – in very good order that I purchased a while back, thinking then that this engine (1,000cc @ 8.5:1 comp) may well prove to be a bugger to start on a magneto The distributor shouldn’t be too hard to modify, either by making a new cam or regrinding the existing one. Certainly a lot easier than a magneto cam ring. Only worry then is whether the rotor arm contact is long enough to reach cyl no 2 in the dist cap.
'49 B31, '49 M21, '53 DOT, '58 Flash, '00 Firestorm, Weslake sprint bike.

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Re: magneto
« Reply #20 on: 19.04. 2019 20:43 »
Have finally diagnosed the points gap / timing problem. Having made some new shims because a couple of the existing ones were a bit tired - and following John’s advice - I  turned the housing back to original and checked gaps / timing. It was then that I found the cam ring bore in the housing was out of true with the armature bearing. Presumably a lot of A10’s and A7’s suffer from the same issue. Not much one can do about that, except maybe open the bearing bore and fit a sleeve concentric with the cam ring.
As noted in an earlier post though, my first job is to see if it’ll run. Hopefully it’ll fire on the rear cylinder and with luck the front will chime in. If everything is hunky dory, I may refurb the mag housing. If not, it’ll be a change to distributor (meaning a battery, charging system etc etc). All of which of course assumes the engine’s a good’un.
Reason I chose the slightly unusual 60 degree configuration is several; I’d already done a 50 deg, I figured on a large-capacity short stroke motor room would be tight between the heads (see pic for lack of room) and lastly it gets closer to Phil Irving’s magic 76 degree.
Happy riding everyone.
'49 B31, '49 M21, '53 DOT, '58 Flash, '00 Firestorm, Weslake sprint bike.

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Re: magneto
« Reply #21 on: 19.04. 2019 21:12 »
G'day RD.
Nice work there mate. Are they XT/SR top ends?
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
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Muskys Plunger A7

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Re: magneto
« Reply #22 on: 20.04. 2019 06:06 »
It was then that I found the cam ring bore in the housing was out of true with the armature bearing. Presumably a lot of A10’s and A7’s suffer from the same issue. Not much one can do about that, except maybe open the bearing bore and fit a sleeve concentric with the cam ring.

Not uncommon RD. But always worth hoicking off the housing and reseating the bearing outer race (if it was in place when you measured the lack of concentricity). They're often a bit 'off' if the insulator isn't perfect or gunge has been used to assist retention and it's one of the first places to go when firing interval and points gap won't play ball. Wear on manual mags between camring and housing is also common. A good wheeze can be the use of self-adhesive stainless steel shim tape 'tween ring and housing to compensate for errors - it comes in a good variety of fine thicknesses and is tough stuff. New housings and rings can be had at a price but most times the bits can be got to within a degree or so, and the points gaps to close to equal. The real test is the firing interval at speed. While it's poss to get things right statically using eg a rotary table, there's no substitute for strobing the running motor obviously. What one sees at 0rpm isn't necessarily what one will see at 4000  . . . .
Fantastic project - deserves to be a big success!
Bill

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Re: magneto
« Reply #23 on: 20.04. 2019 09:31 »
Amazing work! What will that shaft on the right drive? Dynamo? Supercharger? Spinning sword?

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Re: magneto
« Reply #24 on: 20.04. 2019 12:05 »
Musky - both. Couldn't find a pair at the time, so changed an XT head to SR spec (bigger inlet etc) & trimmed the SR fins. As the heads are no longer level, I welded appropriate weirs to the camshaft troughs to contain oil. Also, because inlets have to turn through 90 deg to reach somewhere a carb will fit, I modified the inlet ports to flanges. Barrels are my own.
Greybeard - spot on - shaft on right is to drive an alternator.
Groily - when I was checking concentricity I didn't look too closely at the bearing outer race, but there seemed to be a gap between it and the housing. I presumed one of those bl**dy awful serrated gaskets? Still have some somewhere, if they're the same as BTH that is. They always seemed to slip sideways when I fitted them. BTW the camring is a good fit in the housing.
Only way I can think of re-aligning the bearing bore to the camring - assuming it's possible - would be to turn up a mandrel for the camring bore to sit on and then open up the bearing bore to take a sleeve.
'49 B31, '49 M21, '53 DOT, '58 Flash, '00 Firestorm, Weslake sprint bike.

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Re: magneto
« Reply #25 on: 20.04. 2019 15:21 »
- when I was checking concentricity I didn't look too closely at the bearing outer race, but there seemed to be a gap between it and the housing. I presumed one of those bl**dy awful serrated gaskets? Still have some somewhere, if they're the same as BTH that is. They always seemed to slip sideways when I fitted them. BTW the camring is a good fit in the housing.
Only way I can think of re-aligning the bearing bore to the camring - assuming it's possible - would be to turn up a mandrel for the camring bore to sit on and then open up the bearing bore to take a sleeve.

Yup - the housing is bored to take outer race + insulator cup.
The insulator can be a pita but is a 'good thing' in the sense that you don't want any of the HT current running back to earth via the balls in the bearings and eating away at them over time. (You can see  the effect of return current on the brass of the armature on many a mag, where dimples form on the earth brush track at the firing point(s).)
Probably makes very little odds in anything other than the very long term as long the earth brush/es is/are doing their job, but most mags have the insulators for that reason. They come traditionally in 2 thicknesses, 10 and 13 thou, to allow for wear, machining variations, whatever. Dimensions to suit the various bearing sizes involved. In this case an E15.
Bearings in all common mags are standard sizes, with E15 being used at the cb end on all Lucas K series (except C versions), also on the drive ends of early K series, and at both ends on almost all BTH. Same insulators therefore as what you have, almost for certain.. If your one had slipped in the fitting, or the bore has previously suffered  damage for any reason, it could make a few thou difference to the concentricity.
On some of the early mags that didn't use insulators, it can make it a tricky job to get the outer races out esp from the drive ends, because there's no 'soft' gap to get an expanding extractor tool into.  Lots of them have two wee holes where people have been reduced to drilling the housings and using hard pins to knock the races out - and sometimes they've 'missed' with the drill 'n all!)

Nowt wrong with setting the thing up to overbore and sleeve if you want though - that way you'll know it's right. Sometimes it's a good mod to bore out early K bodies to get them to take the bigger 18mm drive end bearing and fatter armature shafts that arrived in the early 50s. Especially for mags carrying the weight of ATDs, where it's not all that rare to find the steel shafts are loose in the brass drive end cheek. 

Good news the camring's a good fit.

Only other thing to maybe mess with is the points. Sometimes, fitting a new opening point with an unworn heel makes a surprising difference to things.
Bill

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Re: magneto
« Reply #26 on: 24.04. 2019 17:28 »
Just had a thought. Yes, I know, dangerous and all that .... but seriously, it seems to me that rather than boring the casing for a sleeve to fit the std bearing, why not open it up to take the bigger 37mm bearing? From what I can see, the other dimensions are identical - it's just a bigger outer race. Is that correct?
'49 B31, '49 M21, '53 DOT, '58 Flash, '00 Firestorm, Weslake sprint bike.

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Re: magneto
« Reply #27 on: 24.04. 2019 18:55 »
Good idea RD imho. It's just the od of the outer race that is different.
That 15mm id 'N3048' is found on the drive end of (most) MO1s and also at the cb ends of most if not all C versions of Ks. Bit chunkier, no other changes required. Just need to get the thing well-chucked on a mandrel like you said earlier (or even using the camring housing and an independent 4 jaw for that matter - maybe).
Good luck!
Bill

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Re: magneto
« Reply #28 on: 30.04. 2019 06:11 »
having a KVFTT on one of my bikes, my understanding is these mags are known to be marginal on the front cylinder and rarely idle nicely on both pots.
Mine does... but the factory solution was the series D vincent which adopted coil and points , resolved the problem and was much cheaper.
A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
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Re: magneto
« Reply #29 on: 30.04. 2019 09:20 »
Is why all such mag-ignited beasts are better off with an ATD, if it's an option Rocket Racer.
Most Series C Rapides on standard KVFs I've played with have ticked over OK, but earlier bikes with manual advance/retard can be more challenging.

'Resolving the problem' did, though, make the need for a working charging system more crucial than ever, and also consumed some 20% of the available output just to keep the engine running.
This was certainly a drawback on some of the Indians, whose dynamos weren't so hot, half a generation earlier on. Ditto some of the coil ignition Harleys. There are good upgrades for most of those bikes available these days. Just as, nowadays, with an Alton, maybe some LEDs,  big modern battery, electronic ignition if required  . . .  it should be easier on Vincents of all eras too - at a price. Progress!

I'm not persuaded that in the ever-so-'umble world of parallel twins (in stock states of tune) there are huge advantages to some of the more expensive kit - but then that's just my biased view. Where I've been able to fit a mag, I always have 'cos I think they're more reliable than the other leccy bits from back in the day.

PS (for RD) - I bored out a 15mm drive end housing for an 18mm armature yesterday and it came out fine. Face-plate job and modest use of measuring sticks, so the time was in the set-up. Worth it to be able to mix and match available parts economically  . . .
Bill