Author Topic: Magneto Auto Advance  (Read 1969 times)

Offline Stu55Flash

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Magneto Auto Advance
« on: 19.07. 2010 22:29 »
Can anyone help with my 1955 A10 Plunger Flash

I've finally started stripping the engine as far as undoing the auto advance off the end of the magneto. Instead of withdrawing the advance the centre bolt has undone so far and then stopped without bringing the advance mech with it. Is it possible to leaver the mag out the back. Will the advance mech pull off against the case without damaging the bakalite cog? 

Any ideas welcome.

Stu
"Keep a distance from lady "L" drivers in cars. Some are not mechanically minded, are slow to acquire road sense, an are apt to panic..." The Pitman Book of the BSA Twins.
Golden Flash Plunger 1955, Francis Barnett Falcon 67 1954, Ferguson TEA Tractor 1951. Looking for another project!

Offline trevinoz

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Re: Magneto Auto Advance
« Reply #1 on: 19.07. 2010 22:55 »
Stu,
          It should unscrew so far, meet resistance and further unscrewing should release the gear from the taper.

Trev.

Offline Stu55Flash

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Re: Magneto Auto Advance
« Reply #2 on: 19.07. 2010 23:20 »
Hi Trev

It unscrews so far and then just turns. The bolt head is 10mm off the top of the advance mech but then just turns. I think the shoulder has pulled through the mech without the gear pulling off the shaft. Could this happen? With not having one apart before I dont know how it goes together or comes apart. There is a horse shoe washer and cover plate that have come off from under the  nut head. I don't know if it was assembled correctly as the engine has only been put together loosely. I have never had the engine running in the bike.

Stu
"Keep a distance from lady "L" drivers in cars. Some are not mechanically minded, are slow to acquire road sense, an are apt to panic..." The Pitman Book of the BSA Twins.
Golden Flash Plunger 1955, Francis Barnett Falcon 67 1954, Ferguson TEA Tractor 1951. Looking for another project!

Offline trevinoz

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Re: Magneto Auto Advance
« Reply #3 on: 19.07. 2010 23:42 »
Stu,
           It was probably buggered when the last bloke fitted it!
I have never had this problem [yet]. Time for a little experimentation.
A puller won't work as there is nothing to pull against unless you get the nut out.
Try pulling it outwards and turning it clockwise as it has a left hand thread on it's shaft, that's the way they are assembled.
Trev.

Offline A10Boy

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Re: Magneto Auto Advance
« Reply #4 on: 20.07. 2010 12:35 »
If you can get the nut out - which looks like a bolt and as trev says has a left hand thread which engages into the unit when it has unscrewed off the shaft, - you could grind off the remaining outside threads and screw it back in onto the mag armature shaft. This will then give you something to pull against. A small two leg puller could then be used. You will probably need to replace the Fibre gear anyway.

Certainly dont try to lever against the cases.

Andy
Regards

Andy

1960 A10 - Black Golden Flash
Plus
1974 Kawasaki Z1a
Yam XJR 1300

Offline Stu55Flash

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Re: Magneto Auto Advance
« Reply #5 on: 20.07. 2010 18:17 »
Hi thanks folks

Now got it off not quite sure how! Tighten it up clockwise then unscrewed it anti clockwise and it came off. The bakalite cog has a tooth missing [not my doing]. I've seen these on the Dragonfly web site. Are they for the manual advance or can they be replaced?

Stu
"Keep a distance from lady "L" drivers in cars. Some are not mechanically minded, are slow to acquire road sense, an are apt to panic..." The Pitman Book of the BSA Twins.
Golden Flash Plunger 1955, Francis Barnett Falcon 67 1954, Ferguson TEA Tractor 1951. Looking for another project!

Offline MG

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Re: Magneto Auto Advance
« Reply #6 on: 20.07. 2010 18:38 »
Hello Stu!

If you want peace of mind, better buy an aluminium wheel. Draganfly has them listed, but the part's description says "fibre wheel", while the photo shows the Dural one. You'd better ask prior to ordering I guess.

http://www.draganfly.co.uk/shop/pd-2060969223.htm?defaultVariants={EOL}&categoryId=0

I'm using aluminium wheels from SRM, these are not cheap, but they work a treat. I recall some members complaining about wrong teeth profiles, so the wheels were not engaging properly.


The pinion on the auto advance unit can be replaced, it's not a big deal.

Here's some information about disassembly:
http://www.a7a10.net/forum/index.php/topic,1744.0.html

Kindly provided by your best friend, the forum's search function.  *smile*


Cheers, Markus
1955 A7 Shooting Star
1956 A10 Golden Flash
1961 Matchless G12 CSR

www.histo-tech.at - Restoration, Repairs, Racing

Austria

Offline A10Boy

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Re: Magneto Auto Advance
« Reply #7 on: 20.07. 2010 18:45 »
Stu
Good news its come off.

The gears are fiber not bakalite. You can replace them yourself, but first check that the center moves nicely inside the outer bit, some are seized but most are worn badly. If its worn the gear wobbles around and that's what damages the teeth, also check that the tangs on the stops are secure, I've seen some missing or about to break off. If its badly worn you can get them refurbished. I wouldn't be tempted to use one with excessive play.

On the rear of the unit is a collar fitted over the center, it has 3 or 4 punch marks on the joint, lightly drill the punch marks, put the unit in the vice carefully holding it by the scrap gearwheel, and get some grips on the collar, rotate it and it comes off.

Next you can pull the center from the outer saving the weights and springs. Drill out the four rivets holding the gear wheel on, replace the wheel, fit new rivets [3/16 mid steel] and as they say, assembly is the reverse of dismantling. You will need a new center nut too.

Make sure it all moves without binding or you will have problems.

Any questions let me know.
Regards

Andy

1960 A10 - Black Golden Flash
Plus
1974 Kawasaki Z1a
Yam XJR 1300

Offline Stu55Flash

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Re: Magneto Auto Advance
« Reply #8 on: 20.07. 2010 23:21 »
Thats spot on

I will order up fibre or ally cog and rivet it in. Stripped the barrel and clutch off. Barrel and pistons spot on. need to split the case to clean sludge trap. End float on crank is 10 thou measured with DTI seems an awful lot but haynes says 24 thou limit? Pleased so far as not much cost and time involved so far! High hopes.

Stu

 

"Keep a distance from lady "L" drivers in cars. Some are not mechanically minded, are slow to acquire road sense, an are apt to panic..." The Pitman Book of the BSA Twins.
Golden Flash Plunger 1955, Francis Barnett Falcon 67 1954, Ferguson TEA Tractor 1951. Looking for another project!

Offline trevinoz

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Re: Magneto Auto Advance
« Reply #9 on: 20.07. 2010 23:31 »
Stu,
           I would tighten up that end float considerably. I aim for .001"-.002".
Definitely clean the sludge trap and make sure the timing side bush is a good fit on the crank. .0015" clearance is perfect.
Trev.

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Re: Magneto Auto Advance
« Reply #10 on: 21.07. 2010 07:52 »
G'dat Stu,
                that's 24 thou BIG END side play not crank end float. Ditto what Trev says.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
Australia
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Online bsa-bill

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Re: Magneto Auto Advance
« Reply #11 on: 21.07. 2010 08:10 »
Yep crank end float 3 thou max, if you can do it - "measure many times take bearing off once" - is good or measure old bearing and new one accurate if you can then do some sums with the difference and existing crank end float.
Good luck with it anyway
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline A10Boy

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Re: Magneto Auto Advance
« Reply #12 on: 21.07. 2010 13:31 »
Isn't that 3 Thou max on a re-build ??
Regards

Andy

1960 A10 - Black Golden Flash
Plus
1974 Kawasaki Z1a
Yam XJR 1300

Online bsa-bill

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Re: Magneto Auto Advance
« Reply #13 on: 21.07. 2010 14:12 »
Quote
Isn't that 3 Thou max on a re-build ??

Isn't that what we are talking about

Quote
need to split the case to clean sludge trap. End float on crank is 10 thou measured with DTI

This might be of interest Stu item 270609576884 on Ebay
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline A10Boy

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Re: Magneto Auto Advance
« Reply #14 on: 22.07. 2010 18:34 »
Stu
I have a couple of good re-con A/R units if you are stuck.
Regards

Andy

1960 A10 - Black Golden Flash
Plus
1974 Kawasaki Z1a
Yam XJR 1300