Magneto/ignition timing problem?

[bsa-bill]

Ah here we are getting concerned about torque settings, back in the day I wonder how many owners had heard of a torque wrench let alone owned or could afford to own one.
Nope a box spanner with a big screwdriver through the hole in it and pull as hard as you could or get big uncle Fred to come along for Sunday dinner and do it for you.

those were the days

[chaterlea25]

HI Redbeeza,
OOOOPs!!!!
If the magneto is spun over "open circuit" the sparks should jump to the safety gap screw tips!!!!
these are there to prevent excessive build up of voltage in the mag secondary winding!
Hopefully these screws are fitted??
If not the high voltage generated tries to find an escape route through the weakest point in the insulation wherever that happens to be ????
I think the safety gap is around 1/4 in. it takes the hell of a high voltage to jump that, so if there was a weakness somewhere there will be a breakdown in the insulation!!

In you other post regarding valve clearance, 8 and 10 thou is normal, I think 10 and 12 is for max power
neither setting will make problems like you have?

I would remove the rocker covers and see if you can push down any of the valves with thumb pressure
to see if there is a soft spring ????
Set pistons at tdc first

If you have or can borrow a strobe light hook this up on either  plug lead any  misfiring will be obvious as the light pattern is broken . You can just shine the light on the primary or timing covers, no need to have a revolving shaft /disc to look at.
If all that is OK
Then get a colourtune sparkplug and fit it one side at a time, this will show up mechanical misfires if the ignition system proves good

Was the engine recently rebuilt???
Were the valve clearances adjusted if and when the head/base were retightened???
New valves will stretch /or settle a little into the seats tightrning up the clearances
Were / Are the valve clearances set at the correct position ???? ????
Adjust each valve  when its partner is fully OPEN,  Right hand ex fully open adjust left ex. then the other way round

HTH
John  O R

[redbeeza]

Well, I'm certainly learning more about the magneto! The safety gap screws are fitted and now I know what they are for. I have read a lot about the A10 from various sources whilst rebuilding it and have stuff about the magneto too, but I don't remember reading anything about the hazards of spinning it open-circuit, now I do.

I did check it by holding the HT leads about 1/8" from a barrel base bolt and kicking it over, after reading your previous thread John. There was a fairly fat blue spark for each lead but of course that doesn't tell you how they're performing in the combustion chamber.

I'm still following the scored slip-ring as my first line of enquiry. Thanks for the replies on that Triton Thrasher. I did give the ring a cursory clean with some Meths on a rag, but looking at it more closely, I think graphite dust has become more ingrained in the scoring, as Bill suggested, so will try a thorough clean.

I think I will end up having to take the mag off though and try and replace the slip-ring. I've had a read through my magneto info and it doesn't sound easy to change a slip-ring. I'll have to give it a go though because funds have run very low for this project now, my job having gone in the government's cut-backs... I just can't afford to send the mag off to a specialist (£250 went to Mr Lindsley to sort the dynamo not that long ago).

Thanks for taking an interest John. I will try and work through your suggestions if the slip-ring thing doesn't work and thanks for confirming valve clearances, I have them at 8 and 10 thou but had recently read something about opening the gaps up a bit for the 357 cam (nothing to do with the current problem, just another thing I was thinking about).

I will give the head a re-torque seeing as I do have a torque wrench and am pulling the engine about again, but I know what you mean Bill. I did have a small uncle Fred, I don't think he knew anything about motorbikes, but could have taught me a thing or two about beekeeping.

By the way, whilst taking off the rocker-box, not only have I dropped a rocker cover stud down the push-rod tunnel, I notice that the new alloy(!) pushrods have burred over at their tips. And the bike hasn't even been on the road yet!

Now you're going to tell me never to use alloy pushrods in an A10. But if that is the case how can a 'reputable dealer' sell these things for an A10? Are they just for show bikes? I'll have to dig the old ones out and hammer the bent one straight...

I expect I've fitted a chocolate camshaft as well.

[groily]

To change the slip ring, the hard thing's getting the cb-end bearing inner race off the armature Redbeeza. It's usually fairly tightly on.
So, with the mag on the table  . . .
Get the cb backplate off - undo centre bolt (4BA or 1/4AF) and wiggle not too hard, it will come with the points all attached. The cam ring slides out if it's manual, stays if it's fixed (a mag with an ATD). (You may have done all that to get the mag off, if it's a manual one and the advance/retard cable had to come off). Remove the safety screws you know all about now - or they'll hit and maybe bust the slip ring as you pull the armature out of the drive end in a minute. Ditto HT pickups and the earth brush - next to the maker's plate at the drive end. Undo the screws that hold the outer end of the mag on - there should be three - take note of any big shims between the housing and the body (they eliminate negative end float). Pull the armature out. Gently prise off the cage and balls from the offending bearing - note which way round for reassembly if not replacing the bearing.

Coming back to this inner race. There are two problems. You can't get behind it to lever it off, and you have to be very careful not to mess up the tapered brass end piece with its little integral keyway that holds the cb unit. Making it out of round will make you miserable and maybe poorer.
The best way to get it off is to make or get made a split clamp with a ridge in the middle to engage the track for the balls. A ring of steel bored to fit snugly over the whole bearing race and drilled and tapped for brass grub screws to engage the track will do nearly as well - but if you intend reusing the bearing, is less kind to it if it's tight. Do up the split shells/fit ring and tighten grub screws and then use a puller on the whole thing. But - it is pretty well essential to protect that brass taper. A cone of steel or brass with a small shoulder which will sit on the armature shaft and still allow the inner race to pass through as it is pulled is the best thing I've come up with.
With that off, there may be more shims for setting the end float - note them! - and then an oil flinger and the slip ring can be removed. The slip ring is fragile as in brittle. Yours looks a bit tracked from the pic, and there's probably a bit of a ridge where the brass strip is a tad proud of the bakelite. That's normal but not good. The HT coil's live end goes into the lumpy bit at 12 0'clock on the rear - and may be quite well stuck in with shellac etc - so careful's the word. Last thing you want is to bust the wire off the coil.
Sounds worse in writing than it is in practice - but - just my own view - trying to get the race off with little screwdrivers, or by holding the race in soft jaws or a wrap of copper wire (often recommended over the years) and whacking the armature shaft, are no-noes. I learnt this the hard way. You can get away with it on the drive end bearing, maybe, but not here.
Best of luck and very sorry to hear about the job thing.
If you can't sort out a tool, send me a PM and I'll sort something out for you that will do it.

[redbeeza]

Well folks I've finally fixed it, the bike lives again!

It turned out to be a combination of something very simple hidden behind some red herrings, and my lack of experience.  I shall relate it here at the expense of looking foolish in order to complete the puzzle and hopefully help some others out there if they come across similar symptoms.

To recap: Symptoms = difficulty starting; when started, revved too high, wouldn't idle, lumpy running; backfiring; firing on one cylinder; overheating; rapid bluing of exhausts.

Red herring no.1 = broken pick-up brush lying in bottom of mag and black deposits on slip ring.  This led me (after cleaning the slip ring to no avail) to strip the mag down to change the slip ring, which then led me to think I may as well get the mag rewound with a new condenser whilst its off. Three weeks later the mag is back from Mr Tony Cooper. Hurrah.

Mag fitted, complete with new slip ring and brushes. Engine timed to 5/16" BTDC. Starting procedure gone through, kicked over several times: not a whisper. Rechecked timing; it had slipped to about 0" BTDC. Oh no, I think, taper on timing pinion/mag end shaft not gripping.  Decided to check through everything. Noticed points plate centre bolt wasn't tight and points were a little under 12 thou". Took out points and reset to 12 thou". Checked movement of adv/ret lever and cable, this seemed OK, so set back to fully advanced. Then accidentally knocked the handlebars and saw the cam-ring move a little more in the advanced direction: cable was sticking, so I hadn't set the timimg on full advance.

Removed cable and lubricated it and refitted. Reset timing on full advance and tried a start up. Fired and ran on 5th kick. Ran like a pig with exactly the same symptoms as it had before the mag rebuild!

In the meantime I had ordered some new plugs; Champion N4C's and thought I'd give those a try. Tony Cooper had sent rubber plug caps and advised I use them instead of the plastic (unsuppressed) ones that I had. SO, I fitted the new plugs and plug caps and tried a start up again: same problem except that it was running more obviously on one cylinder (the right hand one), although both header pipes were still getting red hot. Checked timing again, it was OK and hadn't moved (thank heavens), removed plugs. Right hand side plug looked OK, left hand plug was fouled with sooty deposits.

OK, so I was making progress: timing was correct and left hand cylinder wasn't firing properly. Right, I replaced the left hand HT lead and pick-up. Started it up: no improvement. OK, so it is no longer looking like an ignition problem, and why the high revs and lack of throttle response?

I had a read through the old posts here on fuel and carby problems and decided it MUST be an air leak or blocked up pilot jet or something similar. OK, I decided to strip down the carby. I unscrewed the pancake air filter and checked (again) the throttle cable and slide and air slide for free movement.

I then noticed that the slide was moving freely enough but when it was 'at rest' there was quite an opening under it. I had no idea how much of an opening ther should be so checked some Amal diagrams I had. It looked a bit too wide to me so I tried unscrewing the throttle stop screw, but nothing happened.

I then noticed the inline adjuster in the throttle cable. It was unthreaded quite a bit. So I threaded it in and watched the throttle slide decend to around an 1/8" opening. I then recalled that way back at the end of the summer of 2009 I'd fitted a new twistgrip.

I still thought that this simple matter couldn't account for the misfiring, overheating, running on one cylinder etc. that I'd experienced, although it would account for the difficult starting and high revs. I was going to continue with carby strip down anyway but then stopped and thought, no, one thing at a time.

So, I screwed in the throttle stop a little way and put the air filter back on. Went through starting procedure, kicked her over....and she fired and ran beautifully. On both cylinders, no overheating, no misfire.

What do you think of that?

Terry

[LJ.]

Dohhhh!  Always the simplest things eh? Thanks for a good readup at your expense. Good Lesson for us all.

[bsa-bill]

Well done Terry, don't worry we have all learnt some of the stuff the hard way and the rest from others who learnt that the hard way.
Now we just need some good weather

[pato08]

Hi All

I have coppied this tread, printed and saved to my ever expanding file for garage wall read for my rebuild

My thanks to all for some very enlightning facts

Pato

[groily]

Great news Terry. And even if it might not have been essential right away, having Tony C do the mag can only be good - one thing not to have to worry about ( as long as that cable stays free!) Just in time for the next blast of cold weather then!

[JohnH]

Well done Terry.

I found your recorded experiences really enlightening (I was going to say enjoyable but realised - just in time that it might be misconstrued!). Like Pato, I've stored away the thread for future reference. Really good learning points and I really don't think I would have been as observant or intuitive as you were. Tony Cooper sounds like a magician .... as does Groily ... I would not attempt to take a mag apart - even with his instruction set.

Well done ... as somebody else said - Bring on some decent weather!!

John

[redbeeza]

Thank you for the comments chaps, it really helps to have a pat on the back for persevering, even if it is only via the web.

A big thank you to Groily also, who gave me encouragement and sent me a hand-crafted device for getting the mag bearing inner race off.

I'm still in the dark over how some of the symptoms were caused by only the throttle slide being open too wide. Why would that make the mixture fire in the exhaust rather than the combustion chamber?  I've read in the Amal literature that having too weak a mixture can cause 'banging in the exhaust' but I can't see why. If it was late ignition timing or valve timing out, I could begin to understand. Can any of you technical boffins explain?

Also, I can see that the mixture might be weaker on start-up because the throttle was open too much, so more air was being allowed in. But surely this shouldn't be the case, because the mixture is metered throughout the throttle operation range by various methods: first the pilot jet; then slide cut-away; needle position; and main jet. If the throttle was open too wide so that the pilot jet couldn't meter enough fuel, then the slide cut-away would take over, wouldn't it? Does this make sense, or have I talked myself up my own exhaust pipe again?

I think I can understand the running on one cylinder though. It looks, from the old plugs, that the LH cylinder runs a bit richer than the RH (and I've read the threads about the 'bias gasket' issues), so maybe this was just exaggerated under these fault conditions to cause the cylinder to flood quicker and douse the plug.

I agree about COME ON with the decent weather. I need to be able to get to the MOT station before the bike decides it wants to hibernate. Must bolt the battery down better first though...

Terry

[iansoady]

If the air slide was working correctly it's possible that you were getting something approximating the correct mixture even though the throttle slide wasn't going all the way down.

I always listen for the tap of the slide on the throttle stop screw to make sure the slide isn't hanging on the cable like yours was. If you put your finger on the throttle stop you can actually feel it making contact.

[bsa-bill]

anybody know about how much of the cutaway should be showing when throttle is closed - is Amal tuning picture about right or is it too much of a variable to declare.
Just trying to get starting sussed on the project, seems to be a totally different method needed to that if the flash

[groily]

A pleasure Terry - and glad it worked.
A while back we were discussing the tools required for getting these bearings off easily, and MG kindly dug out a link to a very excellent German-made chuck-puller, capable of extracting a variety of such small races - up to about 30mm if memory serves. However, they are very expensive, and in any case obviously don't offer an easy means of protecting the brass taper on the cb end of a mag. I didn't buy one. But I've made several, and continue to think it's something the people who make all those pullers for various mag pinions, camshaft gears etc etc ought to add to their list of 'useful possible new products'. After all, pulling a mag bearing race is a simple little thing, and there are gazillions of K series mags out there, with loads of capable owners. Wrapping copper wire round the bearing track and whacking armatures wiv 'n 'ammer (often suggested!) ain't the answer. Plus the fact that other devices also obviously use 15mm and 18mm bearings - Magnéto-France 'Double-Débit' dynamos as but one example I've come across lately from a world adjacent to our own.

[Alan @Ncl]

I am just working my way through Maggy threads and read this very informative sequence which prompted a couple of questions of my own (in addition to the new thread I posted today).  Many years ago I had problems with timing slipping and had eventually to get a new autoadvance as the taper seemed to have worn in the one I got with the bike.  In subsequent paranoia I always used loctite on the taper.  I also slotted the holes in the mounting flange (see pic) to get a bit of leeway for timing adjustment without releasing the dreaded nut.

On eventually removing the autoadvance recently, 30 years on, it took a hell of a pull on the centre bolt (quite worrying actually, as I assume the reaction can only come from the force on the fibre gear teeth).  I wonder if others have had similar issues, concerns or comments?

One other observation.  I downloaded the Excel sheet from  http://www.a7a10.net/ignition%20timing%20converter.xls as I have just finished creating something similar.  My version gives the following output:
5/16 = 32deg, 11/32deg = 33.7deg, 3/8 = 35.2deg,  13/32 = 36.7deg.  These seem similar to values I have seen elsewhere on this forum and to get them, I inputted a stroke = 84mm (= 3.31 inches) and conrod length of 164mm (6.47 inches).  However, I note the stroke used in the timing converter sheet is less than this so it gives different answers to mine so perhaps the data in there is for an A7?  We get the same answers if using the same input data (which is reassuring at least).