Magneto/ignition timing problem?

[redbeeza]

Hello again everyone. I have managed to get back to Blighty through the French blockade, under cover of darkness!

I have now begun to tackle the problem with my bike that I had to leave when I went out to France in March: the magneto/ignition timing problem (please see old post).

Investigation with a mirror and torch showed half a pick-up brush laying in the bottom of the magneto slip-ring housing. Right, ok, that would help explain the misfiring and overheating if it was causing random sparks to fly around all over the place. But I've followed 'red-herrings' before!

I followed advice from my previous posts: I've had the carb off and cleaned out the gunk; I've drained off the old fuel and refilled with new premium unleaded. I have removed the broken brush and cleaned the slip-ring and housing. I have fitted new pick-up brushes.

Put everything back together and tried a start-up. 1/3 retard on the lever: engine kicked-back and spat through carb on first attempt. 2/3 retard on the lever: engine fired and ran on 5th kick. Same trouble as before: uneven running, backfiring, high idle. When I tried easing the adv/retard lever towards advance, engine revs increased. Exhaust headers glowed CHERRY RED in under a minute. Shut engine off.

OK so this looks like an ignition timing issue, yes? Too retarded? Could it be anything else? Will look into timing over the next few days. What I would like some help with and some opinions on are the following:

How could this problem have occured when the bike ran fine 5 months previously and I have done nothing to it, save kicking over the engine occasionally (plugs out) throughout the winter?

Could some of you who have the same bike and tuning set-up as mine tell me what ignition timing value you use? I have a 1962 super rocket; 'big valve' head; 357 cam; and I'm pretty sure I have 8.25:1 CR pistons. I have an Amal 389 carb, 1 and 5/32" bore; 290 main jet (air filter fitted); 25 pilot jet; slide 389/3; needle position 2 (from top); needle jet 106.

The more research I do on ignition timing (and I have searched posts on this forum also), the more conflicting the information gets: Eddie Dow tuning says 5/16" BTDC = 32 degrees; SRM website says 5/16" BTDC = 35 degrees (which I believe is wrong)! Does anyone on the site have an accurate comparison chart for linear measurements and degrees for ignition timing? I'm thinking 5/16"=32; 11/32"=33; 3/8"=34; 13/32"=36.

I have an original BSA Instruction Manual for A7 and A10 twins reprinted March 1963. In the technical data for both the A10GF and the A10SR the ignition timing measurement is given as 13/32". I haven't seen this measurement mentioned by anyone else anywhere! It is always 3/8" or 5/16" that is talked about for the A10. And I know from reading previous posts that all this goes out the window with the use of modern fuels, that's why I've asked for settings that work for people today.

Also, what valve clearances do you guys run with a 357 cam/ally head? 0.10in inlet, 0.12in exhaust?

Cheers chaps and sorry for such a long post!

Tel

[bsa-bill]

I have a little brown book that specifies 13/32 for both late Golf Flash and Rockets, strangely the same little brown book gets the degrees wrong for A7s?
I am not an expert re timing but I'm becoming one due to magneto problems, hopefully now cured, one such problem was that the points cam had  moved, that is it had rotated within the end of the magneto, causing similar problems to yours, it was very difficult to start but once running was ok, the advice given here was I think spot on in that the spark will track from the brass contact on the slip ring to the pickup via carbon on the slip ring so it would run but once stopped would not start again snd no spark would be seen at the plug.
Reason the cam moved it seems is the peg that holds them was not prominent enough into the cam ring (ummmm)
Anyway I would check that the camring is where it should be, looking at the end of the maggie from the primary side there are two screws hold it on, the top one will be about 11 0 clock, the thickest bit of the cam ring should be in line with the screw, mine had moved about 3/4 of an inch.
Doubt if this is the whole answer you are looking for but worth a check'
As for a chart to convert degrees to inches you need to go here http://www.a7a10.net/ignition%20timing%20converter.xls

[chaterlea25]

Hi, Redbeeza and Bill,
Whats foxing my train of thought is that the bike is kicking back on 1/3 retard ???? ???? ???? ????
this would mean that the timing is more or less correct
Redbeeza, have you forgotten which way is advance while you were away from the bike???
Apologies, if that sounds disparaging, I do not mean to cause offence
But it is all I can think of at the moment, the K2F is "normally" slack wire advance!! (lever forward LH side)
If the bike kicks back in one instance and then reddens the ex pipes without moving the timing on the pinion
this is the only explanation I can think of!!
Other Beezas, B31's and such are normally tightwire advance!
Tightwire advance is a real dopey design (or lack of) in my opinion!!!

HTH
John O R

[A10Boy]

I dont think "Cherry Red" exhausts are caused by retarded ingition. Retarded ignition would be like being over rich which would make the engine 8 stroke and the exhausts run colder not cherry red.

I think its just a very weak mixture, has the needle dropped into the jet, or have you removed the air cleaner element and forgotten? Maybe the main jet has partially gummed up while its been standing for months.

[Triton Thrasher]

Retarded ignition roasts the pipes, no doubt about that.

Check that your ignition timing is the same as it was before you had trouble.

[A10Boy]

If it was retarded enough to roast the pipes, it wouldn't kick back on 1/3 retard.

[Triton Thrasher]

If it was retarded enough to roast the pipes, it wouldn't kick back on 1/3 retard.

Probably not and the problem may be only an air leak at the inlet manifold or other trivial fault, but if you suspect ignition timing, you have to check it or you can't eliminate it as a cause.


I read this as you don't believe retarded timing causes red hot pipes.

I dont think "Cherry Red" exhausts are caused by retarded ingition.

[A10Boy]

Actually, I believe my comments are correct if you take them in context of the engine kicking back as I did.

I dont think "Cherry Red" exhausts are caused by retarded ingition. Retarded ignition would be like being over rich which would make the engine 8 stroke and the exhausts run colder not cherry red.

I was merely suggesting that it might not be ignition timing, but could be an over weak mixture, another possible cause which would need eliminating. Er sorry if that caused you some offence...

[Triton Thrasher]

You'll know when I'm offended.

I'll be like this:

[redbeeza]

Well, it's not the ignition timing, that's still ok on 5/16" BTDC. And I haven't got the advance/retard direction wrong, although that was a good point to raise John because I'm always having to double check this and the air-lever (not having ridden the bike yet!). I have the directions taped on the handlebars.

I'm pretty sure it's not a carb problem. I have just had that apart to clean and have fitted new needle, main jet, pilot jet, needle jet, o-ring and I'd renewed gaskets earlier. I checked all these bits for blockages before fitting them and besides, this problem occurred before I checked over the carb.

I had a good look at the slip ring whilst checking the timing and it looks damaged to me. It looks like it has been gouged. The only thing that has happened between the bike running fine and this new problem, as I stated above, is that a pick-up brush broke and lay in the bottom of the mag. Would a graphite pick-up brush be tough enough to gouge a groove into the brass and plastic material of the slip-ring do you think? The brushes are a bit of a sloppy fit, if one of them popped almost out of the pick-up head when I fitted it, or during one of my winter engine 'kick-overs' and got jammed against the slip-ring it could have caused this gouging.



I've tried to show the gouges in this photo. I'm pretty sure the slip-ring wasn't this grim looking before the broken brush episode...

Could this damage cause the symptoms I've described?

Feeling a bit jaded...

[bsa-bill]

If the gouges hold carbon then they will may make very good conducting tracks

[redbeeza]

Good point Bill. Looks like the mag had better come off. Ho hum, farewell quick (and inexpensive) fix. Will I ever get to ride this thing...

[Triton Thrasher]

Have you already rubbed the slip ring clean with meth or petrol?  Hold a pad soaked in such a substance against the base of the ring and spin the engine with the kickstart. Repeat until the pad picks up no more black.  Short out the killswitch to avoid painful shocks to your finger.

They get scored when a brush slips sideways as it's fitted. I know because I've done it.  If cleaning it fixes it but it happens again, you may be able to smooth the base of the slip ring with steel wool.

[chaterlea25]

Hi Redbeeza,
quote from your first post!

"How could this problem have occured when the bike ran fine 5 months previously and I have done nothing to it, save kicking over the engine occasionally (plugs out) throughout the winter?"

Did you have the plugs in the caps and the plug bodies earthed onto the bike when you were kicking it over??
If you left the leads open circuit you may have damaged the mag windings??

The only other cause that I can come up with is one that had me foxed for quite a while on a bike I subsequently had to do a full rebuild on 
This bike would start easily but would not run evenly on both cylinders, missing and shooting flames out, and as you say reddening the exhaust pipe (almost) as I didnt let it run for too long
I believe this bike had been sitting idle as well ???? ????

The cause was a collapsed exhaust valve spring 
It would return the valve fine as the engine was kicked over but wouldnt return it fast enough when running
so flame out the pipe
Compression test was fine, on the kickstart even with the dead spring

HTH
John O R

[redbeeza]

John, don't say things like 'you may have damaged the mag windings'!  That's not what I want to hear.

No I didn't have plugs in caps and earthed on the bike, but I know I'll never turn an idle engine over again in the mistaken belief that I'll do some good.

I thought these bikes were meant to be reliable workhorses in their time, easily maintained by the average guy with pretty basic mechanical knowledge...

I'll be able to have a look at the valves when I take the head off again. I may as well do that when I re-torque the head. A local expert advised 18-20ft/lbs and it seems that the guys on here wind on twice as much as that!