Newbie Questions- timing

Information relating to the Matchless G9 or AJS Model 20 500cc twin
Sams Dad
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Re: Newbie Questions- timing

Post by Sams Dad »

Ok Clive, I withdraw the question. I had no idea. I am just desperate to sort this problem. The problem appears worse than I thought and those parts will not solve it! The three holes on the housing do not align with the TWO on the mag body. They are diagonally opposite and are both the same thread. I was trying to screw into a dead end. I presume this means that the two parts do not match ? Is there a two holed points housing ? Anyone have one or can point me in the direction of where i can find one ? It looks as if this will solve the problem once I have the correct fasteners whatever they may be to hold it all together.
Groily
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Re: Newbie Questions- timing

Post by Groily »

There are two-holers and three-holers, and details differ in terms of fixing and screw lengths, and also the cb end cover. Some are for fixed camring mags, some for manual advance. I'd say there were at least a dozen variants over the years, not counting Competition mags which are different again.
Sounds as if you have the alloy dome type, with a press-in button to stop the engine? That would be very normal on these bikes. And the design that needs the awkward special studs . . . woe.

Most end housings use different screws from yours and also have a bakelite cover, until the later big screw-on ali one was introduced. Some of the variants need long screws and some short, some a mix, but they all do the same thing basically, which is hold the bearing and the camring and the advance and retard gubbibns. You want to keep what you have if it can be made to serve.

A two hole cover can be fine, and the one with the ali dome needs those two special fasteners as you say - 2BA on the inner end then a blank section, then more thread on the outer end for nuts that hold the dome on. That is, unless a threaded hole on the mag main body has been taken out to anything else, which does happen, in which case a helicoil or other insert would be required, or a special stud making up . . .?? A slightly fiddly design with flats on the plain section to allow the end housing to be tightened without the dome being on there. Not sure where these can be had, as opposed to made, but always worth trying Dave Lindsley Magnetos. I can't be sanctioned cos I haven't got any!
Often, there'll be a third short screw on the bottom right hand side. But there are many covers of various designs with just 2.

Mag bodies can have anything up to 4 holes. Some have 2, some 3. All are fine, in the correct combination. On my Mod 20, with alloy dome and button, there are the two long special studs and one short 2BA screw bottom right. I am assuming the 'ears' for the fasteners are on the correct diagonals, top right and bottom left looking at the points, and that there ARE threads in those positions on the body?? Some 'ears' are set the other way about, but usually that would be for a mag with the advance and retard entering on the gearbox side, not the engine side.

Yours is probably quite OK, just needs the fasteners. You don't need to change the housing, but if there's a blank hole on the mag body where a screw should go (bottom right?) then it says the housing and the mag body didn't go together from Day 1. No problem, as long as the bearing is concentric, etc etc per previous comments. At some point a third hole could be drilled and tapped if you ever wanted.

For present purposes you could just use some 2 BA screws to hold housing on firmly, and see what happens to the points gap; don't try to run a mag without the cb cover though - the camrings have a nasty habit of going for a walk. If things look better with the housing correctly attached temporarily, then a solution to the correct stud problem is next.
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clive
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Re: Newbie Questions- timing

Post by clive »

Sams Dad wrote: Sun Jun 06, 2021 10:18 pm Ok Clive, I withdraw the question. I had no idea. I am just desperate to sort this problem.
No problem. The private message system allows you to contact someone directly either by message or by email if they have registered one. Alternatively you can start a new thread in the members only section of the forum marked adverts. Here discussion and requests for parts etc are all legitimate. If people review 'new posts" the advert part of the forum appears in the same way the rest does.
I had no idea the complications of the twin mag i have obviously been lucky in my two forays into this area. N1 mags for the singles are a doodle by comparison. Good luck with sorting it out.
clive
if it ain't broke don't fix
Sams Dad
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Location: Lancs UK

Re: Newbie Questions- timing

Post by Sams Dad »

Hi Groily, that all makes sense now! I have on the points housing 3 holes - i tried to post photos but I am not sure how to do it - . : two at the bottom and one to right.
but on the casing one top left and one bottom right, so nothing for either of the two deeper cover hole screws to go in to. The holes do not align if I rotate it through 90 degrees or even 270 so that is why I thought they do not match. It would work to drill and tap the body bottom left and top right I think. Top left the housing is shaped for the manual a/r so there is no ear there to drill or that would have worked.
You said - 'On my Mod 20, with alloy dome and button, there are the two long special studs and one short 2BA screw bottom right. I am assuming the 'ears' for the fasteners are on the correct diagonals, top right and bottom left looking at the points, and that there ARE threads in those positions on the body??'
You are right it is the alloy dome type and the housing and cover are like yours, but the main body is not. That has two holes top right and bottom l left ! So in answer to the last question, nope the threads are in the wrong positions. I think I need bottom left and top right drilling and tapping on the main body. However, I think this will solve the first problem, allowing the housing and points housing to be held flat, which should give me even points gaps, but i will then need the special fasteners to be made/bought to complete the job. Do you agree ?

(edited to remove duplication of text -Clive as moderator)
Sams Dad
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Re: Newbie Questions- timing

Post by Sams Dad »

Thanks Clive! I think we are getting there now!
Groily
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Re: Newbie Questions- timing

Post by Groily »

Right, got the picture in my head now, no need for a photo. And you've got it clear in your head too.

You have got a mag body probably originally designed for a fixed camring housing and an auto-advance unit on the drive, per BSA etc etc, with holes top left and bottom right. So, the 'wrong' diagonal for the ears on the housing - which goes under the heading 'General Embuggerance'.
I doubt the bike was ever really run like that actually, as the end housing ear at bottom right, being the sole means of attachment and the flimsy one of the three to boot, would have broken off. They break off easily enough anyway!

So, yes, you do need to drill and tap some holes if you are to retain these parts. The housing is the right one, the mag body is the wrong one, and as changing the latter isn't a cheap or easy option . . . worth getting to grips with what you've got I think.
Obviously the hole at top left is redundant with the AR bits in the way, so you'll end up with 4 holes. No problem. BUT it is soooo important to drill and tap with complete accuracy.

The mag will HAVE to come off the bike.
You can get away with not taking the whole thing to bits if you very carefully position the end housing where it needs to be on the main mag body and do up that third screw nicely. If there is the slightest 'wiggle' (see previous discussions) then try the points and camring for fit and equal gaps etc before tightening the third screw. And check again when tightened up afterwards! Use also, if you can, some sort of clamp to hold the 'other side' tight against the body as well, because 'flush' is also critical to the final fit. (Might be able to contrive that using one of the pillars for the HT pick-ups and wire twisted round the AR fitting.)

Then, make 'dots' for the tapping drill to follow with a slim centre punch, through the deep holes in the housing. A punch that fits them snugly, with its point sharp and on centre, would be a huge advantage! A good drill bit could also be used. Like this, you'll get the hole centres near enough spot-on.
The fasteners are countersunk at mid point where they hold the housing on, so is the third screw head, and you don't want them pulling the housing off-centre when you do things up, or fighting each other as you tighten them. Worst of all you don't want to have to let out the holes to get the thing to go on. I have been here, and it's a hard place to get out of!

With the inside of the end housing protected against swarf with clean rag, drill the holes. 3.9mm is good for 2BA but I can't give you an exact depth. About 5/16" of thread engagement probably. The mag will need to be mounted dead vertically by the drive end flange on a stout base allowing the armature shaft to stick through it, and a sturdy drill press (or even a miller if you know someone with one) is what's needed. Personally, I'd swap the drill for a 2BA taper tap immediately after drilling the first hole, without moving anything, so the thread isn't drunken. Then I'd remove the mag, finish the hole with a 2nd or bottom tap, put a screw in and do it up. Check for fit, camring, points etc as before. With any luck all is straight and true. Then drill the other hole.

I know this makes it sound hard. But . . if you think how a very small error in camring position affects the points gap and by association the firing interval, you can see I'm not really exaggerating the need for serious accuracy. At the factory these holes and threads would have been done on a drilling jig, a luxury we don't have - and whenever I have had to do this particular operation, I have had heart slightly in mouth - and I have taken my time!
If all goes well, you get an armature that is turning true and concentric to the axis of the mag; you get a camring housing that is square to the mag body and with the bearing concentric to it; you get a centrally disposed camring and a contact breaker that turns in a true circle, equal points gaps and, with luck, a decent 180:180° firing interval. As I said before, the interval matters more than the gaps, but everything should be close - couple of thou difference on the gaps maybe, couple of degrees MAX error on the firing interval.

It's all in the preparation and the care taken in doing the job, so although it's a bit of a kerfuffle, it's not actually that hard. Says he! Good luck!
Sams Dad
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Re: Newbie Questions- timing

Post by Sams Dad »

Thank you so much for this careful and thorough guide. I think that is all doable and I have friend, who is a Matchless man as well, who I think will have the right tap and a lathe on which we may be able to make the studs I need. I have metric taps, but not imperial ones. He is away currently, but I hope to so speak to him later in the week. I will l key you know how i get on.
Clive , apologies about the duplication. It all went wrong. I copied and pasted as it would not submit but I managed to paste it three times. I thought i had deleted all of the duplication. It is awkward on my phone. Sorry.
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clive
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Re: Newbie Questions- timing

Post by clive »

No problem Stephen I was seeing double and had not touched a drop! The system times out if you take a while to write your entry, no need to copy and paste simply press submit a second time and it seems to work. Advice is if you are writing war and peace then compose it in word, and then paste it in once you are done so there is no risk of loosing it (been there :headbang: ).
clive
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Sams Dad
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Re: Newbie Questions- timing

Post by Sams Dad »

Ah I see, every day a school day. Thanks for that. I hope to get the drilling done by weekend and will report back.
Sams Dad
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Re: Newbie Questions- timing

Post by Sams Dad »

Latest update- drilled and tapped the opposite 'ears' on the mag. Went slow and seems ok. I need some 2ba studs now and believe they are hard to find so may have to cobble something together. Thanks for all your help and patience so far. If anyone has the correct pattern for the studs that might help. Would a longer bolt straight through the points cover and housing in to the body not work ? I guess it will make setting the points and timing more difficult though.
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