Author Topic: Auto-Advance Magneto question  (Read 10521 times)

Offline flatdeck

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Re: Auto-Advance Magneto question
« Reply #15 on: 10.10. 2007 01:44 »
Still struggling with getting this A7 to go. We have recently set the timing to points starting to open at TDC whilst fully-retarded (per Munro - Thanks Jeff) and it certainly sounded like it wanted to start (coughed and spluttered a bit). We have since tried advancing it about 2mm on the points each time and are now about 10mm from where we started. Still she is not starting. We are spraying Engine Start into the carbs, and tickling the floats till the fingertip is damp with petrol, so I don't think fuel is the problem. I'm fairly happy that we have tried a broad range of timing so I have to wonder whether we are getting sufficient spark. How do you tell? I see bright blue sparks when the plugs are out of the cylinders but does that necessarily translate to sparks in the cylinder? Can the compression that is generated suppress the spark in the cylinder enough to stop it igniting the fuel?
Dave
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1949 A7 Star Twin
Kent, U.K. then Auckland, N.Z.

Online Brian

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Re: Auto-Advance Magneto question
« Reply #16 on: 10.10. 2007 02:29 »
If you set the points to open when at TDC and fully retarded that should be close enough for it to run. You can check the spark by disconnecting the plug caps from the lead, leave the plugs in and hold the end of the plug lead about 1/4" from the spark plug cap. Kick the bike over and see if you have a spark. If you have tried spraying easy start in the carby and it didnt do anything then you have something wrong, it should at least fire a few times. Have you checked that you have the correct plug lead going to the correct cylinder? To do a simple check take both plugs out, hold you finger over one plug hole and turn the motor over until you feel pressure against your finger, then bring that piston up to TDC, you should have this cylinder on its firing stroke at this stage. Once you have done this follow the plug lead from this cyl back to the maggy, remove the pick up from the maggy and look in the hole [may have to use a mirror] you should be able to see the brass strip on the pick up ring. If there is no brass strip visible swap the plug leads over. Hope this helps, Brian.

Offline 1KCBC

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Re: Auto-Advance Magneto question
« Reply #17 on: 10.10. 2007 02:46 »
Try and try flatdeck,Brian gave you a good idea and for the compresstion,it should not suppress the spark.
Have a nice day. *work*
Jaran.
1951 A10GF,(looking for  A10 swinging-arm)

Offline flatdeck

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Re: Auto-Advance Magneto question
« Reply #18 on: 10.10. 2007 04:18 »
Hey, thanks Brian. Last night we sat looking at it for 10 mins doubting ourselves having adjusted the timing for the 4rth time and having been rewarded with a short splutter at best. We shall start at the beginning again and check we have TDC, that we understand which way is BTDC looking at the points, that we have a spark (thanks for the tip Brian) and that we have petrol in the cylinder. We didn't think the compression would be enough to snuff out the spark we were seeing.
Cheers,
Dave
p.s. What else would I be doing :-)?
Dave
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1949 A7 Star Twin
Kent, U.K. then Auckland, N.Z.

Offline fido

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Re: Auto-Advance Magneto question
« Reply #19 on: 10.10. 2007 08:20 »
If an A7 or A10 won't start it is nearly always due to magneto trouble. Obviously things like spark plugs and valve clearances also need to be checked but is there any way you could borrow a different mag to try?

Offline flatdeck

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Re: Auto-Advance Magneto question
« Reply #20 on: 15.10. 2007 22:02 »
Hi guys, more testing last night. We are happy the timing is as it should be. Checked the brass strip was in view when piston at TDC and it is. We have fuel, timing and compression so we can only conclude that the spark is just too pathetic. We are getting a blue spark across the plug gap but if we disconnect the lead from the plug we are getting nothing jumping from the lead to anything. The plan is to replace the fibre drive gear (that has a tooth missing), hopefully removing a some play in the magneto drive, and then investigating whether electronic ignition is the way to go. Has anyone here replaced their magneto with CDI? Any info on this would be appeciated, especially on where the ignition gets its timing (I would prefer to get it from the crank if possible avoiding all the sloppiness in the mag drive. Cheers,
Dave
Dave
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1949 A7 Star Twin
Kent, U.K. then Auckland, N.Z.

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Re: Auto-Advance Magneto question
« Reply #21 on: 15.10. 2007 22:43 »
Hi, Flatdeck personally I would not bother with electronic ignition ,Best bet is to get your magneto checked & reconditioned & replace timing gear.As for setting ignition timing  I use an old oil pump worm drive with a bolt welded into centre to take a degree disc I screw this onto crankshaft & use a dial gauge into plug hole to find top dead centre then set disc to zero degrees useing a pointer attached to crankcase ,once set turn crankshaft backwards to remove slack in timing gear then turn clockwise to 34 degrees before top dead (GOLDFLASH)  if you have auto advance magneto pinion you need to make sure this is fully advanced with points just begining to break open once happy with position of points tighten centre nut on pinion.you can then check for equal timing on both cylinders on degree disc .This should make for a smooth running motor.  Dave..

Offline flatdeck

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Re: Auto-Advance Magneto question
« Reply #22 on: 15.10. 2007 23:02 »
Hi, thanks Dave. I am finding out so much as I go along ... mainly that there are so many favoured ways of doing things! I would prefer using the existing technology but a couple of chaps have suggested EI improves the reliability for about the same price as a magneto check/rebuild. There are a couple of guys reasonably near me that rebuild mags so I might just take it off and get them to do it and see how we go. I have to buy a fibre drive gear and replace it anyway though because there is definitely play in that. Have to see how much is in the pocket money jar ...Cheers,
Dave
Dave
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1949 A7 Star Twin
Kent, U.K. then Auckland, N.Z.

Online Brian

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Re: Auto-Advance Magneto question
« Reply #23 on: 15.10. 2007 23:27 »
Hi Dave, sounds like your maggy is definitely dead. If it wont throw a spark when you still have the plugs in then its cactus. Personally I would rebuild the maggy. If you do give the maggy to someone to rebuild make sure they rewind it and replace the condensor, not just clean it up etc. I would only give the maggy to someone that has a good reputation. Good Luck, Brian.

Offline flatdeck

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Re: Auto-Advance Magneto question
« Reply #24 on: 16.10. 2007 04:07 »
Decided on where to spend the money. New fibre drive gear and a test and repair as necesasry on the magneto. There's a guy within 10 minutes drive from work that specialising in magneto rebuilding ... I'd call that providence / a clue :-). Whilst that is all happening I guess I'll do some polishing.
Dave
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1949 A7 Star Twin
Kent, U.K. then Auckland, N.Z.

Offline flatdeck

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Re: Auto-Advance Magneto question
« Reply #25 on: 23.10. 2007 20:48 »
Update: Magneto went to the magneto specialist last night. A quick revealed small, weak and pathetic spark from one plug only. Remagnetised the mag with the result that it is a hopeless case and will neeed rewinding apparently. New fibre drive gear for the AAU in progress from the UK. I'm spending the next 4 weeks polishing and cleaning waiting for bits....
Cheers,
Dave
Dave
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1949 A7 Star Twin
Kent, U.K. then Auckland, N.Z.

Offline snowbeard

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Re: Auto-Advance Magneto question
« Reply #26 on: 20.11. 2007 20:46 »
so here's a question spurred by groily's description of his "smart mate"

if you get the magento drive gear cinched down tight and realize that you're off by just a little on the timing, couldn't one simply move the cam ring in the end plate to adjust timing as well? or is that not a good idea for one reason or another?


I have a strange confabulation of a mag, it has the manual advance static fibre gear, but the auto advance static cam ring and end plate.  but with either correct system, moving the camring should be acceptable, no?

I'll qualify this question wiht the information that I don't understand how the field collapse and slip ring, etc all interact, sounds like if you took the cam ring too far it might not open in conjunction with the slip ring brass/pickup coincidence?
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Offline flatdeck

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Re: Auto-Advance Magneto question
« Reply #27 on: 20.11. 2007 21:09 »
The camring has a keyway that locks it in place stopping it from moving unintentionally .... I haven't investigated inside the magneto at all ... so can't comment
Dave
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1949 A7 Star Twin
Kent, U.K. then Auckland, N.Z.

Offline snowbeard

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Re: Auto-Advance Magneto question
« Reply #28 on: 21.11. 2007 06:13 »
I see that in mine, but my cam ring notch is at least 1/4 " away from it! 

it must be a testament to these bikes that mine ran at all!! wobbly armature, no advance, camring off kilter!   

or the PO, maybe he wasn't entirely crazy...

I hope to hear how yours runs so well when you get your mag back! *smile*
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Offline flatdeck

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Re: Auto-Advance Magneto question
« Reply #29 on: 21.11. 2007 20:14 »
Apparently I can't expect the mag back till Xmas  *sad2*. I am a bit disappointed to say the least having been told 4 wks a month ago. Oh well, lots of cleaning to do ....
Dave
NZBSAOC
1949 A7 Star Twin
Kent, U.K. then Auckland, N.Z.