The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: owain on 20.05. 2017 19:57

Title: Installing the auto-advance magneto unit
Post by: owain on 20.05. 2017 19:57
I was hoping to set my timing today but I couldn't get tighten the bolt that attaches the auto-advance unit to magneto spindle enough. There is a large washer and a 'C' shaped washer behind the bolt but when the bolt is fully tightened there is still a 4-6mm gap between the bolt and the washers (so they just fall off!). I've checked the diagrams and can't see any other shim or washer that is supposed to be there. I also removed the bolt and checked that it was able to go all the way down to the bottom of the threads on the magneto spindle, no problems there. Is there something else I'm missing?
Title: Re: Installing the auto-advance magneto unit
Post by: morris on 20.05. 2017 22:42
Were both your magneto and AR unit a pair before?
When there's 4-6 mm left, that's the point where the thread normally just starts to engage.
Title: Re: Installing the auto-advance magneto unit
Post by: Greybeard on 20.05. 2017 22:50
I'm sure someone will soon provide a definitive reply but I think you need to make sure the bolt is not still in removal mode. There is some kind of BSA magic that allows the retaining bolt to extract the ATD.
Title: Re: Installing the auto-advance magneto unit
Post by: RichardL on 20.05. 2017 22:58
Greybeard said exactly what I was thinking while writing the following:

I'm going to take a stab here, someone will correct me if I'm wrong. It sounds like you are trying to start theading the bolt onto the magneto shaft while the extraction thread is still engaged in the pinion. Make sure the bolt is threaded all the way into the pinion and spinning freely before starting it on the magneto shaft.

Richard L.
Title: Re: Installing the auto-advance magneto unit
Post by: Greybeard on 20.05. 2017 23:03
Greybeard said exactly what I was thinking while writing the following:

I'm going to take a stab here, someone will correct me if I'm wrong. It sounds like you are trying to start theading the bolt onto the magneto shaft while the extraction thread is still engaged in the pinion. Make sure the bolt is threaded all the way into the pinion and spinning freely before starting it on the magneto shaft.

Richard L.


Beautifully put Richard.
Title: Re: Installing the auto-advance magneto unit
Post by: RichardL on 20.05. 2017 23:10
Thanks. Now, if only we are right. ;)

Richard L.
Title: Re: Installing the auto-advance magneto unit
Post by: duTch on 21.05. 2017 00:14

 Both what I had in mind too, but I'll add that if (owain) you're not aware the 'bolt' which is also a 'nut', also has a left hand thread, which does the extracting, so you need to turn the 'nut' until it disengages and spins free- then push it to engage the armature and it'll screw on (that's GB's 'BSA Magic' )..something along those lines  *conf*

 If I'm describing how to suck eggs let me know, I haven't had brekky yet *smile*
Title: Re: Installing the auto-advance magneto unit
Post by: Triton Thrasher on 21.05. 2017 07:56

Look at the little section of left-handed thread on the outside of the nut. When you unscrew the nut from the magneto shaft, that thread pushes the auto advance off the taper. Turning it clockwise unscrews it out of the auto advance (if you can get the thread to catch).

(http://forumbilder.se/DBKCI/20140128-183216.jpg)

You have to do most of the loose hand screwing onto the magneto shaft while pulling the auto advance outward against the hex head of the nut, so that thread doesn't catch in the outer yoke
Title: Re: Installing the auto-advance magneto unit
Post by: owain on 21.05. 2017 18:54
Cheers for the advice! I made sure the bolt was spinning freely and it worked a treat. The pinion is back on snug!

But...I noticed that the thick washer (distancer?) on the rear of the ATD pinion was cracked. I sort of repaired it with a weld but would prefer to buy a new one except I cannot find the part number anywhere. Does anyone know it??

Title: Re: Installing the auto-advance magneto unit
Post by: beezermacc on 21.05. 2017 23:18
New ones not available to the best of my knowledge. I'll send you a good used one if you let me have your address (by PM) and you pay the post.