The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: RDfella on 13.04. 2019 20:07

Title: magneto
Post by: RDfella on 13.04. 2019 20:07
Here’s a query for the magneto geniuses.
I have a Lucas KVF on a 60 degree vee twin. Trouble is, the manual advance comes out at a very awkward angle, so I’d like to rotate the cam ring / advance holder through 180 degrees. Were this a parallel twin, I’d not see a problem but, being a 60 degree engine, I’m concerned that doing this might have the points opening out of kilter with the armature.
Any thoughts?
 *????*
Title: Re: magneto
Post by: muskrat on 13.04. 2019 23:30
G'day RD.
I'm probably the least knowledgeable with magies but can you rotate the whole mag 120 degrees by the flange.
Cheers
Title: Re: magneto
Post by: groily on 14.04. 2019 07:58
RD - you can rotate the camring and not have anything out of kilter - you just need to reverse the HT leads as well.
The rear cylinder on an engine whose crank turns clockwise from the timing side will be the one fired after the shorter period of 'points closed', the front one after the longer interval (as that's the one that is running 'late' at the mag). The firing interval is 150:210°, or should be if the camring is a 60° one.

Manual control on a 60° V engine means the mag has to be in super good shape. In the advanced position the second cylinder is already running 30° retarded from the ideal firing point, and with additional retard applied, that second spark will become appreciably weaker still. (You can't compromise the setting by asking one cylinder to fire 'early' because it won't, as the HT coil won't be charged up. But you DO want to get that first spark to arrive as early as possible, ie with the camring as 'advanced' as you can safely get it in its housing; that way the delay on the second lobe is minimised.

Couple of supplementary things:
Traditionally, the second, weaker spark on a V is arranged to be the negative one (spark goes from centre electrode to earth on plug), so reversal of the magnetism is a good move if possible. (Doesn't make THAT much odds, but every little helps.)
Also it's very worth checking the HT brushes' position on the brass strip of the slipring at full advance and full retard on both cylinders with the points just opening- to be quite sure the brush is always fully on the strip at the firing points. The typical slipring on a KVF is stretched, with manual advance/retard, on a 50° application, so this isn't a trivial point. I haven't tried a KVF at 60°, but I can say that a manual mag from an HRD needed every millimeter of the brass strip on the ring to cover the range. It might just  be that a reduction in camring movement to limit retard would be necessary, because if the spark flew partly  across plastic or bakelite, trouble wouldn't be far away!

Have to say, my heart sits in my mouth when testing wide-angle V-twin mags, as the requirement to get that second spark at reasonable rpm is pretty important for easy starting. On a 50° V, the difference in rpm required to promote the 1st and 2nd spark would typically be about 30 or 40 rpm, with the first spark (5.5mm Lucas-spec test gap) delivered (100% continuously) at under 130 rpm (at best). That's 260 crank rpm rising to 320-340, say. Doesn't sound a huge lot - but in kickstart terms  . . .
Title: Re: magneto
Post by: Greybeard on 14.04. 2019 08:08
Groily, you are a font of knowledge!
Title: Re: magneto
Post by: groily on 14.04. 2019 08:31
Not at all sure about that GB. A little learning and all that!! Dangerous or what?!
But  . . . V twins are fun to play with, and they do offer some interesting twists because no magneto was ever really designed to function assymetrically. Demanding they do so means you're always starting from a compromised position. The wider the angle, the more compromised. Bosch did some good stuff on 'staggered' armature design to try to compensate for assymetry on Vs, and other folk did similar.  Lucas though, with the KVF, basically just asked a K2F to do its best, with minor tweaks. And they work surprisingly well for all that, it does have to be said.
Title: Re: magneto
Post by: RDfella on 14.04. 2019 18:34
Thanks for that folks.
Musky – if only I could! The mag is mounted vertically and unfortunately rotating 1/3 turn clockwise or anti-clock ends up with the cable pointing away from the bike; the other way puts the adv/ret pointing straight at the rear cylinder – hence my wish to rotate the cam ring and adv/ret assy by 180 degrees (which is possible provided I drill & tap one mounting hole) to get it pointing rearward.
Bill – lots of good info there. Have tried to wrap my head around this but got brain fade. Seems to me if I rotate the cam ring 180 degrees, on a parallel twin I’d merely have to swap plug leads, but on a 60 degree there’s no cylinder firing 180 degrees later (or earlier) so I’d need to move the timing 30 degrees forward or back. Which is where I start getting brain fade trying to figure whether that means points won’t be opening at the most appropriate time in relation to the armature.
Or is it that, as you say, that the mag was designed for 180 degree firing and in that case I’d merely be swapping over the cylinder likely to get the weaker spark with its partner – albeit having to retime the ignition in relation to the engine?
I had the mag rebuilt and converted to 60 degree when I started this project, but that was a few years back and I can’t remember who did it. Probably DH Day. It hasn’t been used since then and it’s only now that I’m trying to finish off the project (before I get to old to do so!) that I'm finding these issues.
Having said all that, I have a similar mag on a 50 degree vee twin. Works great, but it’s clear that on starting one cylinder is more enthusiastic than the other one. Often wondered why Brough etc used twin mags on their vee twins.
Title: Re: magneto
Post by: chaterlea25 on 14.04. 2019 20:49
Hi RD and All,
Last year I was working on a 23 HD model F whiich has mag ignition, It has a Bosch magneto
However the cam and end assembly with the advance lever were on the "wrong" side of the mag to work with the linkage from the A/R twistgrip
The cam ring is held in the moving part by screws, I  undid  the screws and rotated the moving part 180 degrees leaving the cam ring in its original position, cutting a new slot for the A/R limit peg and drilling new holes for the cam screws

So with the KVF would it be possible to cut new slots in the cam ring for the A/R plunger and limit peg 180 degrees away from present position, then rotate the housing 1/2 turn
hopefully then keeping the sparks jumping in the correct direction

 *pull hair out*
John
Title: Re: magneto
Post by: groily on 15.04. 2019 07:02
Tis very possible John. Renotching and moving camrings is always an option, as is modifying the cb assembly to reposition the integral keyway (to get the points to open at the right moment with the camring or housing in an altered position). Both these things have to be done regularly when battling with some of these old beasts. (New Lucas camrings usually come blank, so you can grind yer notches wherever you want.)

What matters on a V is that at full advance the points just start to open a few degrees after a flip point for the 'advanced' cylinder. The trailing cylinder will then be correct if the camring is the right one. (Always ensuring the required rotation of the mag has been borne in mind!)

A good example of variations in camring and AR cable position in practice is between, say, the BTH on a Rudge (with AR cable coming off almost horizontally) and the same mag on a Velo, with the end housing 90° differently-placed to have the cable coming off vertically. Same basic instrument but the camring is set differently in the end housing. (And BTHs are a bit harder to modify  than Lucas, but that's another story.)

Reversing a symmetrical camring by 180° on a  parallel twin makes no odds to which plug lead goes where RD. But on a V with an assymetric ring, you gotta get the sparks up there in the correct sequence. It's a one-way-only thing.
If the mag you've got there has been modded, I hope the HT brushes stay on the brass of the slipring in all positions of the AR lever/camring. It's a fine line sometimes between having enough arc of brass to support the AR movement, and not having so much that the thing tries to fire both cylinders at once because both brushes are in contact in certain positions. So yes, twin mags per Brough can be good - where there's the room!
Title: Re: magneto
Post by: chaterlea25 on 15.04. 2019 19:44
Hi Bill, and All,

Been there and done that on the Rudge BTH  *red* ! In my defense it was a very long time ago
But it still happens, a friend got the BTH for his Rudge back from rebuild a while ago and the A/R was vertical so he undid the end screws and turned the housing, then wondered where the sparks had gone to  *eek*

I have a V twin ML mag where the pickups are angled, I,m presuming this is so the will line up with the slipring brass segment better than at 180 degrees?

John
Title: Re: magneto
Post by: groily on 16.04. 2019 06:11


I have a V twin ML mag where the pickups are angled, I,m presuming this is so the will line up with the slipring brass segment better than at 180 degrees?




Yup - there are a few V mags like that John, where the HT pick-ups are offset. And I'm sure you're right as to 'why'.
Title: Re: magneto
Post by: RDfella on 16.04. 2019 13:15
This morning I thought I’d celebrate my birthday by getting to grips with this mag issue. Apart from fitting the occasional bearing in a BTH (and struggling with those insulating gaskets) I’ve tended to leave building mags to those who do it regularly. Which is why I don’t fully understand what I’m doing here. I realise the armature has to be timed with the points, but don’t know how you locate max flux – or, indeed, where it should occur.
Anyway, I took the mag off and job no 1 was to verify that at both adv and ret both slip rings were under the brushes. So far so good. I then marked the case as to where the drive gear was for each points opening. I then reversed the cam ring holder and checked again. I noticed that the asymmetry had swapped sides. The front cylinder points were now opening later than previously (bearing in mind that they were rear cylinder originally) and the rear cylinder earlier (again, bearing in mind these were formerly the front cyl points).  I think.  Which presumably is correct. Designing cams was easier than this!
My next plan is to test the mag for spark at each pickup, which will presumably verify whether the change is do-able. If that’s OK, I’ll go ahead and drill / tap the 3rd hole and refit / retime the mag to the motor.
And if anyone’s wondering why I’m discussing vee twins on this forum, well, it is in a ’62 Golden Flash frame.
Title: Re: magneto
Post by: berger on 16.04. 2019 13:37
o yeah I just love those bearing insulators , I had to make a sleeve up to keep bearing away from magnet power. a bit fiddly diddly but got it in ok
Title: Re: magneto
Post by: groily on 16.04. 2019 17:14
Happy Birthday RD!
Sounds as if you're getting there, no sweat. It will work, it really will.
Very good news that the brushes are on the brass in all positions of A/R - that's one headache you won't have - and it's a great project by the sounds of it.  Cheers!
Title: Re: magneto
Post by: RDfella on 16.04. 2019 20:44
One step forward, one back..... Will get there eventually though. Good blue spark, about 5/16 long from rear cyl pickup, weaker one from front, as expected. Fitted mag and timed it - or tried to. When the rear cyl is timed (approx 30 deg adv) the front is nowhere right - almost 50 deg of advance. Although the mag is marked KVF 60, I'm wondering if the cam ring is actually a 50. And the points gap is greater on the front compared with the rear (.020 / .012) which doesn't help either. So it looks like I'm in need of a decent 60 deg cam ring. What fun bikes are.
Title: Re: magneto
Post by: chaterlea25 on 16.04. 2019 21:18
Hi RD
It probably the end housing is not concentric when turned around, if you follow me
Put the end housing back and check the points gap again and measure the firing intervals
You probably will have to re centre the end housing

John
Title: Re: magneto
Post by: RDfella 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.
Title: Re: magneto
Post by: RDfella 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*
Title: Re: magneto
Post by: chaterlea25 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
Title: Re: magneto
Post by: groily 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  . . .????
Title: Re: magneto
Post by: RDfella 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.
Title: Re: magneto
Post by: RDfella 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.
Title: Re: magneto
Post by: muskrat on 19.04. 2019 21:12
G'day RD.
Nice work there mate. Are they XT/SR top ends?
Cheers
Title: Re: magneto
Post by: groily 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!
Title: Re: magneto
Post by: Greybeard on 20.04. 2019 09:31
Amazing work! What will that shaft on the right drive? Dynamo? Supercharger? Spinning sword?
Title: Re: magneto
Post by: RDfella 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.
Title: Re: magneto
Post by: groily 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.
Title: Re: magneto
Post by: RDfella 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?
Title: Re: magneto
Post by: groily 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!
Title: Re: magneto
Post by: Rocket Racer 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.
Title: Re: magneto
Post by: groily 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  . . .
Title: Re: magneto
Post by: RDfella on 24.05. 2019 18:35
Chaterlea John was correct as usual.
A couple of weeks ago I got around to turning up a mandrel to locate the mag end cap on its cam ring bore. I kept it a thou or so oversize and warmed the casing so it’d grip the mandrel. Also cut a slot for the camring locating screw, to act as drive peg should the cap try to slip whilst being machined. The idea was to rebore the armature bearing so the camring would be concentric with the armature. I was amazed how much out of true it all was. The bearing bore clocked .005” (.0025” off centre) but the real culprit was lack of squareness. I had to take .020” off the flange that locates on the mag casing just to get it to clean up. I also deepened the bearing bore a similar amount, as I didn’t fancy making any more of those outer shims.
Today I re-assembled the mag and remounted it on the engine. Success, the points gaps are now equal and the timing between cylinders spot on (instead of 20* difference). What amazed me was the amount everything was out of kilter. This was not wear or abuse, but sheer bad machining from new. Casting the cap would be dead easy and machining it should only require two or three jigs, so why Lucas made such a pig’s ear defies understanding. Maybe there was crud in the jig that didn’t allow the casting to sit properly when the ‘technician’ did his particular part of the manufacture. Wonder how many came out like that before quality control or the shop’s fitter spotted the problem
Title: Re: magneto
Post by: Triton Thrasher on 24.05. 2019 19:17
Can you engineer something better than the paper daisies, to insulate the bearings?
Title: Re: magneto
Post by: RDfella on 24.05. 2019 20:12
Agree, those bearing insulators are a real pain. As expected, first fit of the bearing wrecked the gasket so had to get another (should have some somewhere but can't find them). Always had hassle with those gaskets / insulators - the trouble is that despite bending the tails around the bearing first, the gasket still tends to slip sideways so that one side is still halfway out. I believe ceramic insulated bearings are available, but they wouldn't be our type and the mag would need modification to fit them.
Title: Re: magneto
Post by: groily on 25.05. 2019 07:09
They are a pain RD - but they do come in 2 thicknesses, and usually with a warmed housing and the nearer fit of the 2 they'll slip in OK, especially the ones with a shiny outside surface.  A non-ferrous mandrel on the end of a non-ferrous bar (with a nose to retain the oil seal over the race and insulator for drive ends) will ensure centralisation.
One of the commonest reasons for problems at the cb end is the skewed fitting of bearing insulators, messing up the concentricity of the outer race viz à viz the housing.
Title: Re: magneto
Post by: duTch on 25.05. 2019 09:22

 
Quote
......This was not wear or abuse, but sheer bad machining from new. ...........

 That machinist deserves a DCM...... *eek*
Title: Re: magneto
Post by: Greybeard on 25.05. 2019 18:26
That machinist deserves a DCM...... *eek*
Distinguished C**t Medal?
Title: Re: magneto
Post by: muskrat on 25.05. 2019 19:11
Don't Come Monday in other words sacked, fired.