Author Topic: Plunger cush drive  (Read 928 times)

Offline wilko

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Plunger cush drive
« on: 27.09. 2014 02:29 »
Does this look right? I would have thought the two contours would match each other? 

Offline wilko

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Re: Plunger cush drive
« Reply #1 on: 27.09. 2014 02:34 »
Another view. 

Offline Resto-Rob

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Re: Plunger cush drive
« Reply #2 on: 27.09. 2014 05:42 »
From what i remember mine was the same.  I think that if they were to match each other they wouldnt be able to move as easily therefore reducing the cushioning effect.  Im answering this before my first cup of coffee in the morning, so dont take my word for it! ;)
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Offline duTch

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Re: Plunger cush drive
« Reply #3 on: 27.09. 2014 05:53 »

 Yep, I reckon what Rob said, I also had a panic. They should match better as you rotate one back and forth, you'll see the scallops ramp up on each other, if yea know what I mean....?
  You'd probably be pressed getting any better.....if you do let us know....?
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Offline cotterpinkid

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Re: Plunger cush drive
« Reply #4 on: 27.09. 2014 08:42 »
Looks good to me
A10 GF Plunger
Velocette Venom

Offline wilko

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Re: Plunger cush drive
« Reply #5 on: 27.09. 2014 09:40 »
It's just that every other cush has a matching profile. The 4 lobe one does. I wonder what BSA were thinking this time?

Offline Topdad

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Re: Plunger cush drive
« Reply #6 on: 27.09. 2014 10:31 »
Just a bad day in small Heath???
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Online muskrat

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Re: Plunger cush drive
« Reply #7 on: 27.09. 2014 11:48 »
The two lobe provides a lot more cush.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
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Muskys Plunger A7

Offline morris

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Re: Plunger cush drive
« Reply #8 on: 27.09. 2014 21:36 »
Looks just like mine Wilko. I also wondered if it was correct like that, but by luck I came across an NOS 2 lobe sleeve on a bikejumble last Sunday. Don't have a picture of the new one because it's on the bike but I can confirm the form of the cam is exactly the same as the one I took out (picture below is from the old one)
'58 BSA A 10 SA
'52 BSA A 10 Plunger
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Offline wilko

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Re: Plunger cush drive
« Reply #9 on: 27.09. 2014 23:53 »
Thanks, will go with it then.

Online RichardL

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Re: Plunger cush drive
« Reply #10 on: 28.09. 2014 03:28 »
It's just that every other cush has a matching profile. The 4 lobe one does. I wonder what BSA were thinking this time?

Not that I know, but it seems that the curve of the upslope on the asymmetrical plunger version was designed to be gentle (hyperbolic?) at first, getting more positive (less cush) as the lobes rode up on each other. My guess is this led to excess wear near the peak of the lobes and they came up with the more roundy symmetrical lobes to even-out the forces. Don't ask me for the math.

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Offline olev

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Re: Plunger cush drive
« Reply #11 on: 28.09. 2014 06:56 »
Wilko,
Just had a look at my 52 A7.
The cush drive is identical to yours.
but mine is prettier.
cheers

Offline duTch

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Re: Plunger cush drive
« Reply #12 on: 28.09. 2014 08:16 »

 Yes Richard, I'm picking up what you're putting down, but not sure if they had sine waves in mind when they designed it on a Friday arvo at the pub..... *conf*

    *beer*
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia