The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: coater87 on 28.06. 2017 20:31

Title: Auto advance gear swelled up?
Post by: coater87 on 28.06. 2017 20:31
 While attempting to fit the AA unit to the bike, I am struggling.

 The gear teeth will not mesh decent with the cam gear. I cannot get the unit to line up with the magneto shaft without jamming the teeth together.

 The teeth on the AA are black, and when I put a little welly into it I see light tan marks and some of the black cardboard seems to roll back.

 Now because this bike is really many different bikes, did they make different cam gears with different teeth profiles for the A10? Part number seems right, from memory its 67-337 stamped into it. But I have learned that could mean little or nothing...

 Is the gear on the AA unit shot from being oil soaked, can it be saved or needs replacement?

 This minor set back is really screwing up my vacation. *conf*

 

 Lee
Title: Re: Auto advance gear swelled up?
Post by: JulianS on 28.06. 2017 21:08
Dont suppose the AA unit is a 50 tooth Triumph type rather than 44 tooth BSA type?
Title: Re: Auto advance gear swelled up?
Post by: coater87 on 28.06. 2017 22:26
Good thought Julian, I gave it a quick count before trying it.

 Now I don't know much about these cardboard gears, but it was pretty soft feeling. I know I KROILED it and sealed it in a zip lock a long time ago. It was one of the few B.S.A. parts I got with this mess.

 Now I know the gear train parts are miss matched, but I messaged the mesh on those and they are a nice fit.

 Knowing I was probably not using this mushy thing, I got it to install by loosening the mag then bringing it all together at once. Turning over the motor it ground it's way to a fit, then broke.

 Damn I have some weird problems. *conf*

  Lee
Title: Re: Auto advance gear swelled up?
Post by: chaterlea25 on 28.06. 2017 23:06
Hi Lee,
The fibre gears have a definite lifespan  *sad2*

Kits are available to replace them

My bikes have manual magneto's and alloy gears  *smile* *smile*

John
Title: Re: Auto advance gear swelled up?
Post by: Black Sheep on 29.06. 2017 06:54
Is it just possible that being sealed in a zip bag with KROIL (what's KROIL?) had an adverse effect on the fibre gear? It looks like it turned it to mush. Fibre gears chucked in  a drawer last indefinitely.
The fibre gear has 2 functions. One is quiet running, the second is to provide a weak link should the magneto, for what ever reason, seize. It would then lose a few teeth without anything else being damaged whilst the engine went quiet and stopped.
Title: Re: Auto advance gear swelled up?
Post by: JulianS on 29.06. 2017 09:43
Very useful guide with photos to stripping the unit on beezermac website

https://sites.google.com/site/priorymagnetos/tech-tips-1
Title: Re: Auto advance gear swelled up?
Post by: coater87 on 29.06. 2017 13:32
Is it just possible that being sealed in a zip bag with KROIL (what's KROIL?) had an adverse effect on the fibre gear? It looks like it turned it to mush. Fibre gears chucked in  a drawer last indefinitely.
The fibre gear has 2 functions. One is quiet running, the second is to provide a weak link should the magneto, for what ever reason, seize. It would then lose a few teeth without anything else being damaged whilst the engine went quiet and stopped.

 Hi Julian,

 I think you are correct, the Kroil (spray on penetrating lube/oil just  like WD40) probably killed it. Maybe even loosend whatever glue holds the cardboard together.

 I knew it was going to be stored for a good while, and I wanted to protect it a little. I have a cement block shed with a tin roof, everything rusts if I dont spray it down.

 I use a lot of Kroil, not because I am part of the Kroil gun cult, but because the smell doesn't bother me.

 I ordered a new fiber gear, will come up with some 3/16 rivets and change it out. It does not look like a bad job, it just popped up when I least expected it. Obviously now I have no idea where I am at with the mag, so I am going to move on to chains and cases for the primary.

 Lee
Title: Re: Auto advance gear swelled up?
Post by: coater87 on 02.07. 2017 15:27
 Wife just let me know the fiber gear arrived in the mail...on Friday. *conf*

 Anyway, it has the right number of teeth, but it is slightly different than the original.

 It is 1/8 inch thicker over all, and does not have the dished out portion that the original did.

 Can this be installed "as is" or do I need to modify the new gear to be like the old? Im just concerned the extra thickness might bite me later.

 Lee

Title: Re: Auto advance gear swelled up?
Post by: JulianS on 02.07. 2017 16:47
Not sure what you mean by dished out portion, but the photos show a NOS A10 unit. Cannot measure the pinion as it is now in the bike.
Title: Re: Auto advance gear swelled up?
Post by: coater87 on 02.07. 2017 16:56
Here is my A.A. unit. You can see the dished out portion in the fiber gear.
Title: Re: Auto advance gear swelled up?
Post by: coater87 on 02.07. 2017 17:00
More.
Title: Re: Auto advance gear swelled up?
Post by: coater87 on 02.07. 2017 17:16
 I sure hope this is not the wrong AA unit for this bike. I have been keeping it safe for 27 years. *sad2*

 
Title: Re: Auto advance gear swelled up?
Post by: JulianS on 02.07. 2017 17:31
I think it is Triumph.

I count more than 44 teeth on your photo aa3? . The dish is a Triumph feature. The mechanisms dont interchange, being thinner the mechanism is shorter and would not fully fit through the new thicker pinion and allow enough length for the retaining to be pushed fully on to secure the mechanism.

I think you need a replacement.
Title: Re: Auto advance gear swelled up?
Post by: coater87 on 02.07. 2017 17:44
 Julian,

 I just found the picture of the triumph unit.

 I swear I counted 44 teeth in the garage, now I marked tooth and got 50. *sad2*

 I need to do some thinking about this.

 Lee
Title: Re: Auto advance gear swelled up?
Post by: beezermacc on 02.07. 2017 19:04
The dished ATD in the picture is definitely Triumph
Title: Re: Auto advance gear swelled up?
Post by: coater87 on 02.07. 2017 23:30
 Well, the parts bike turned life long project strikes again. *sad2*

 At least I can sell the triumph AA unit, besides the gear being mushy its in really good shape without any slop at all.

 Does anyone know anything about the reproduction AA units? They dont look bad in the pictures.

 Lee