Plunger cush drive

[wilko]

Does this look right? I would have thought the two contours would match each other? 

[wilko]

Another view. 

[Resto-Rob]

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!

[duTch]

 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....?

[cotterpinkid]

Looks good to me

[wilko]

It's just that every other cush has a matching profile. The 4 lobe one does. I wonder what BSA were thinking this time?

[Topdad]

Just a bad day in small Heath???

[muskrat]

The two lobe provides a lot more cush.
Cheers

[morris]

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)

[wilko]

Thanks, will go with it then.

[RichardL]

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.

Richard L.

[olev]

Wilko,
Just had a look at my 52 A7.
The cush drive is identical to yours.
but mine is prettier.
cheers

[duTch]

 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.....