Author Topic: B31 Cush Drive  (Read 245 times)

0 Members and 1 Guest are viewing this topic.

martinh10

  • Blue Star
  • **
  • Posts: 62
    • View Profile
B31 Cush Drive
« on: 28 July, 2021, 07:25:25 »
My plunger B31 is fitted with what appears to be a non-standard nut on the engine cush drive (see photo). It has two plain diameters, one to locate the spring and the other being small enough to allow the splined sleeve to slide over it if the spring is sufficiently compressed. This would allow the engine sprocket to ‘cam’ over onto the next lobe. The standard 65-2520 nut only has the one diameter to locate the spring and would limit the movement of the splined sleeve to the end of the spline on the crankshaft. This would not allow the sprocket to ‘cam’ over. My question is: with the standard set-up should there be sufficient movement of the splined sleeve to allow ‘camming’ or should it be limited by the nut?

Pete C

  • Royal Star
  • ***
  • Posts: 238
    • View Profile
Re: B31 Cush Drive
« Reply #1 on: 28 July, 2021, 12:57:27 »
the modification should not make any difference to the function. SRM nuts (they have a hexagon to tighten) also have this double diameter. The movement is controlled by the spring and the lobes should not ride over each other in any situation (agreed the single diameter nut should just prevent this even if the spring is weak). If they do then you either need a new spring or you can use a spacer to pre-load the spring.
When you kick over the engine against compression the lobes should not rise more than halfway up each other.

martinh10

  • Blue Star
  • **
  • Posts: 62
    • View Profile
Re: B31 Cush Drive
« Reply #2 on: 28 July, 2021, 13:22:45 »
Thanks Pete - that's exactly what I needed to know.