The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: Pecon on 06.10. 2012 13:35

Title: Problem refitting AR unit to magneto
Post by: Pecon on 06.10. 2012 13:35

Hi all

I am having a problem locking up the bolt on the AR unit on my magneto after a rebuild. When I start to screw in the bolt the gear pulls onto the taper and the gap between the horseshoe shaped washer gets larger until the washer falls out with a gap of about ¼ inch or more between the bolt head and the washer.  The bolt is locked up at this point.
When the engine was being dismantled a friend removed this part and I have to admit I was not paying attention to what he was doing, unfortunately he is now away on holiday. I have removed and refitted the unit a dozen times but can see no obvious reason for my problem.  I know that I am probably doing something idiotic (not for the first time  *sad2*) but this has left me scratching my head.  If anybody can point me in the right direction I would be grateful. 
Peter
Title: Re: Problem refitting AR unit to magneto
Post by: Flatboy 1950 on 06.10. 2012 14:34
Sounds like you are unscrewing the bolt , instead of tightening it !!
Title: Re: Problem refitting AR unit to magneto
Post by: bsa-bill on 06.10. 2012 15:09
difficult to explain this one but the bolt is self extracting, when the A/R unit is to be removed the nut is slackened then you continue to slacken it, doing so pulls the A/R of the taper.

when you put it back on the bolt should be slack in the A/R unit, most of us will have encountered your situation at some time, keep at it I'm sure you'll get it

Title: Re: Problem refitting AR unit to magneto
Post by: Triton Thrasher on 06.10. 2012 16:54
Away from the bike, hold the unit and screw the nut anticlockwise until it's right in and gets to its externally unthreaded portion under the hex head.

As you then screw it onto the magneto shaft, hold the ATD and keep the nut pushed into it, so the coarse external threads on the nut don't catch in the matching threads in the yoke.

This is the same stuff Bill said.
Title: Re: Problem refitting AR unit to magneto
Post by: Pecon on 06.10. 2012 17:46
Now I'm really confused  *sad2*. It seems to be a clockwise thread as I can screw the bolt in by hand and while the bolt stays the same distance out the unit pulls itself onto the taper, when I then go anti clockwise it pulls off the taper again. Sorry to appear thick but I'm sure I'm missing something obvious.

Peter
Title: Re: Problem refitting AR unit to magneto
Post by: Triton Thrasher on 06.10. 2012 19:48
The internal thread that screws onto the magneto shaft is right handed.

The coarse thread on the outside of the nut (that looks like a bolt) and its corresponding internal thread in the hole in the yoke, are left handed. That is so they can push against each other, without engaging, to take the ATD off the shaft taper when you unscrew the nut.
Title: Re: Problem refitting AR unit to magneto
Post by: Pecon on 11.10. 2012 18:14
Thanks for all the help guys, I kept at it and suddently all fell into place as Bill said.