Contact breaker back plate

Information relating to the Matchless G2 or AJS Model 14 250cc Lightweight
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Contact breaker back plate

Postby davehutch » Mon Dec 29, 2008 3:08 pm

On my G2 the back plate which the contact breaker screws to (043118), seems to be worn and when I try to set the gap or timing its difficult to get it right because when you loosen the screws on the back plate it moves from side to side a little. Has anyone had this problem? What can I do? Can I even buy a new back plate?
I have tried sitting it on a piece of glass to see if it is flat but the screw for adjusting the contact breaker stick through as does the rivet that holds the bracket for the felt pad.
Any help will be appreciated
Thanks in advance Dave


Edited by - davehutch on 29 Dec 2008 3:31:52 PM

Edited by - davehutch on 29 Dec 2008 5:11:10 PM
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Contact breaker back plate

Postby davehutch » Fri Jan 02, 2009 7:12 pm

Can no one HELP
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Contact breaker back plate

Postby Dougie » Fri Jan 02, 2009 7:32 pm

Sorry Dave, I can be of no help but what I have learnt over 35 years of old Brit bike ownership is that setting the points gap and/or the timing is not an exact science.

Experience has shown me that 1 degree, 1 sixteenth of an inch, and 1 or 2 thou do not make any noticable difference to an "old plodder". Never having owned a performance machine of any kind proved right my theory of "Near enough is good enough"!

I know purists and pedants will attack me but you need to remember how the machines were used in their day and how they were maintained. A fiddle here and a bodge there always got you to work throughout the week.
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Contact breaker back plate

Postby dave16mct » Fri Jan 02, 2009 8:36 pm

Hi Dave, what exactly is moving? The points, the cam or the backplate? Or are you loosening the screws too much? Cheers, Dave.

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Contact breaker back plate

Postby davehutch » Fri Jan 02, 2009 8:45 pm

quote:

Hi Dave, what exactly is moving? The points, the cam or the backplate? Or are you loosening the screws too much? Cheers, Dave.


Its actually the backplate,I realize you only need to loosen it a bit, but it can then be moved side to side. The back plate is not a great fit in the recess, and it looks like itís had some hammer in the past.

Thanks Dave
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Contact breaker back plate

Postby itma » Fri Jan 02, 2009 9:09 pm

If I have read this right, you are adjusting the points gap by moving the back plate in its slots?
A very odd thing to do.
the points gap is altered by moving the contact breaker bottom contact.
I may have misunderstood, I am raddled with man flu

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Contact breaker back plate

Postby Merlin » Fri Jan 02, 2009 9:19 pm

raddled!!!!!!!!!!!! What colourSorry moderator could not resist
Chemists do it with test tubes

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Contact breaker back plate

Postby davehutch » Fri Jan 02, 2009 9:22 pm

If you set the points to the right gap thatís fine, But as soon as you loosen the back plate to set the timing the plate moves a little bit sideways which alters the gap again.
Hope this makes more sense.
Dave
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Contact breaker back plate

Postby itma » Fri Jan 02, 2009 9:47 pm

all right raddled and befuddled now
It should not do this.
How much difference in the gap does this sideways movement make? I can't see that if everthing is as it should be it would amount to much.
Is the advance unit pegged on its taper? I can't remember, if not I would suggest that you try and set the timing with the screws in the middle of the slot and move the advance unit on its taper.
best bet would be to replace the backplate; or set the timing then readust the points gap, it will happily function between 12/18 thou, or less; old Trimuphs had the timing adusted soley on the points gap setting.


Anyway I shall be out play again tomorrow, I dont think I am making much sense night nurse beckons, and sadly not the one in stockings, whose pic I shall not post as merlin has been so rude and he seems to have sheep on the brain tonight

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Contact breaker back plate

Postby chris kelly » Fri Jan 02, 2009 9:52 pm


Hi Dave,
I was sitting here thinking exactly what Ken (itma ) has just said.

I know we are talking about the lightweight...... but for example looking at Fig 30 , page 64, in ''The Book of the AJS all models 1955.. 1965 by Haycroft.... the parts breakdown....
1, Contact breaker plate ( fixed)
2.Capacitor
3.Contact plate adjustable
etc, etc

It is the 'contact plate ,adjustable that you have to adjust , not the back plate. You perhaps need to get an illustration such as I have mentioned above to figure it out...but I think the principles follow through, just the design changes a little.

I am looking at a 1966 contact set for the lightweight...some changes from your model date, (1960 ? ) and I have a little contact breaker plate which allows the gap to be enlarged, reduced. That plate is fixed to the bottom plate, the big round one.

It could be , for your model..043118. Base plate unit

and 043115 Base plate only, I think this part number is the one you need to adjust.

Best wishes, Chris.
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