Air head rocker-arm bearings
 

Hi all,
Just checking the valve clearances on my R100GSPD, and found a needle bearing roller lying in the valve cover. On removing the rocker arms, I found that the bottom cage of one of the rocker arm bearings had broken/worn away, allowing the needles to drop down through the slot in the mounting block, into the engine via the push rod tunnels. Removing the sump found three more needles. All are now removed and the offending bearing remains have been replaced.
This is not the first time I have come accross this on various air heads.
Does anyone know why this happens, or if there is a way to stop it happening again?
Cheers

The reason this happens is because the bearing cage is not sunk deep enough into the rocker. It should be in about 2-3 mm from the end surface. Also, once you replace one cage, you really should replace all eight. You can drive them out with a socket and long bolt, big washer on the bolt/washer end, basically pulling the socket through the rocker.