AJS & Matchless Owners Club

Inadvisable I'd say, although those who dwell at the the more brutal end of the mechanicking spectrum may disagree!
Levering and/or whacking has to risk damaging the inner timing cover or even bending the armature spindle if the sprocket is on really tight.
I'd beg, borrow, buy, or make an extractor frankly, as it's something you're bound to need from time to time if the bike's a keeper.

Hi all, more question i have brought the advance unit and a new cover tried to fit it and it seams tne armature thread is larger than the nut on the unit so what size nut is normally on the magneto is it the 1/4 whit as on the cam end Thanks .also am i timing it right tdc valves shut back 1/2 inch full advance 003 mm gap at points or just turning a lamp on tried both, tdc 12 thou points gap at best just getting back fire here and there tried 180 degrees and firing exhaust as expected

It's not 1/4 whit, no.
The armature thread on an SR1 (or N1 or any other of the mags on classic Brit iron) is 3/8 BSF, always. Unless it's been recovered at a smaller diameter after a minor disaster.
The female thread on the central bit of the ATD you've got will also be 3/8 BSF, if it's for a magneto. They all are. (What have you done with the previous mod to the mag by the way? Locked it up, swapped out the bits? It needs to be out of action if you're putting a correct ATD on.)
If the two bits won't go together, maybe the first thread of one or the other is a bit messed up, and needs a bit of tlc.

Not sure what thread's on the cam sprocket, but perhaps 5/16ths BSF or BSC, which would take a '1/4 Whit' spanner? (I don't have any singles.)

A magneto won't tell you when the points are open when using a light, because there is always virtual continuity across the points (open it's the half ohm of the primary winding of the coil, closed, it's zilch ohms in theory if all is clean and sparkly - not enough difference to affect a bulb).

There are other threads here on setting the timing, but basically, get the piston to the right number of mm/in or degrees before top dead centre on the compression stroke - valves both shut, yes. Wedge fully open the advance unit on the mag with a bit of wooden peg or similar. Rotate mag in its direction of normal rotation - anti-clockwise that is from the drive end - until the points are JUST starting to open. Gapped to 12 thou give or take. Be sure the direction is right or you'll be opening the points on the wrong side of the cam which leads to 'unhappy'. There's been plenty of that about, we've all done it probably and conveniently forgotten what eejits we were.
Hold everything steady and do up the centre bolt on the ATD. Done.

OR - I believe many people prefer to do up the ATD first, get that end all shipshape, and only then position the camshaft sprocket on its taper, because it's easier. As I say, I don't have any singles. The principle is the same either way - points just starting to open, full advance, piston x mm or y°BTDC on compression. Sometimes things move as you do things up, the little swine . . . so always best to turn the engine over a few times and check all the measurements one final time.

thank you got a tap n die ordered to clean the thread up as its a mess .I have locked the other end up just with a screw thread for time being , had a light on a 9 volt battery just to see when points opened , also cleaned tapers and going to run tap into advance nut as looking very old up there. Lock tight also on way and some longer casing bolts for bigger case. hope its all running for next month

Stevecampy wrote: ↑Thu Oct 21, 2021 6:38 pm had a light on a 9 volt battery just to see when points opened

Hi

As Groily has said - a bulb and battery will not indicate when the points open on a magneto, (unless there's something amiss internally with the mag). You need to use a cigarette paper, thin feeler gauge or one of these:

http://www.aoservices.co.uk/info/MTL.pdf

Regards Mick

You've done well to find and get all the bits together in such short order. Fingers crossed she fires up and runs well when you get to that stage!

Mick D wrote: ↑Fri Oct 22, 2021 7:07 am
As Groily has said - a bulb and battery will not indicate when the points open on a magneto, (unless there's something amiss internally with the mag). You need to use a cigarette paper, thin feeler gauge or one of these:

http://www.aoservices.co.uk/info/MTL.pdf

Regards Mick

You could also invest in one of these..

Whatever the advice is in the owners manual I have never been able to set the timing correctly trying to lock the sprocket on the magneto. Something always slips especially with the auto advance unit. This has a system which acts as an extractor as well as tightening the unit. Pretty clever but it can be difficult to lock it back on. By far the best method is to lock the magneto sprocket onto the magneto whether Sr1 or N1 then do the timing with the cam sprocket loose. (As suggested by Groily above). The specialist timing devices I alluded to in the above advert are readily available at any tobacconist and are to the factory recommended specification. They will certainly work better than a bulb and battery on a magneto!

clive wrote: ↑Fri Oct 22, 2021 8:59 am By far the best method is to lock the magneto sprocket onto the magneto.

Is what I have read many times from you folk who know all about singles!
When there isn't a centre screw on a cb unit to hold (gently) in a socket while you get the drive sprocket / pinion started on its taper, it's always harder.
Someone should make and market a cam-holding weapon for doing SRs I reckon . . . tubular bar with cam-shaped hollow recess at one end and a T bar . . . Just thinking on the keyboard . . .

And don't get me started on the auto extract thing with ATDs Clive. Omigod it can be sooo hard to fix them when the centre bolt won't come out. Who in the world would have designed a system that required the first turn of the left hand thread to take the full load of extracting a tight taper ? ? ? ? But someone did, presumably driven by an accountant at Lucas . . .
The drive attachments I use when playing with mags on the bench rely on proper internal shoulders, and haven't worn out in a dozen years of heavy use. Any competent person in the drawing office could have designed better, and no competent engineer should have been happy making them the way they were. Rant over.

+1 for Clive's post, above. I personally find a light tap with a soft mallet sticks the sprocket onto the cam taper and all's good to tighten up the nut.

This nut needs very little force. The stub appears to be "waisted" and over energetic spannering can (will) snap it off. In my defence, I was then only 21ish and it was all new to me.

Also +1 for checking when you think you've finished.

Remember to remove the bob weight wedge, I usually use one long enough that the outer mag chain cover will foul it.

Johnny B