Took clutch cover off last week to change clutch springs, and found the crank shockabsorber was past its prime.

would have been noisy on sunday.

Okay I give up! What is a "crank shockabsorber” ? Does it fit into the onumbtanium diaphragm?

Okay I give up! What is a "crank shockabsorber” ? Does it fit into the onumbtanium diaphragm?

Oh Billy, you are soo funny! I have one them in my crank. I gotta ck it cause it leans a bit as well!

The crankshaft on a MAR isn't physically connected to the primary gear.

There's a sleeve over the crank taper that the primary gear spins on and a cushdrive arrangement transmits the power from the crank to the primary gear.

The above spring tensions the two halves of the cush to allow the crank to drive the primary gear.

Seen here

http://www.custgp.com/a1manual2/Ossa%20Mar%20250%201972%20parts.pdf

Parts 991119, 20, 21 and 22.

Though Unobtanium does come into it, it's the name of the tool that removes this custdrive's sleeve from the crank.

Feckinimpossiblium is the process of pulling the sleeve off the crank taper without the tool!

Edited February 2, 201511 yr by goudrons

I must have been luck as the MAR ones have always come off OK for me, the Gripper needed warming up with oxy/ acetylene to get it to let go, but that had possibly never been apart before...

Got to be a better system than the 348 mont that just uses an unkeyed taper for the same drive take off though...

Better to get the correct puller, they are available new from Marlimar OSSA along with the spring.

These "face cam" cush drives used to be common especially on single cylinder british 4 strokes. Some consider a primary chain (rather than a gear) also gives the gearbox an easier time and gives more grip.

Wonder if any trials engine manufacturer has ever experimented with different drive cushioning systems to see which gives most grip at rear tyre?