Crankshaft/main bearings

Marcelo from Brazil contacted me regarding main bearings and crankshaft end float. There were a number of variations used by Triumph, balls both sides, rollers driveside and ball timing side and ball driveside and roller timing side. I decided on a lipped roller for the driveside, both for its load bearing capacity and because it allows an easier assembly of the crank, and a ball bearing for the timing side which, being clamped to the mainshaft by the pinion gear, positively locates the crank. Both bearings were C3 clearance.

My bike origionally had a ball driveside and roller timing side. The roller timing side was secured by a circlip together with a 'chipshield' (a large steel washer which apparently stops gear pinion chips from the timing case entering the bearing). As the variants that used a ball timing side did not use the shield, or the circlip, I left them out.

Crankshaft end float should be between 3 and 17 thou (measured with a dial guage). Its a good idea to measure it BEFORE you seperate the crankcases. Mine was 17 thou (measured before the crankcases were origionally seperated) and the conrods were central in the bores. The endfloat was adjusted with a 3 thou shim both sides which gave 10 thou endfloat with the new bearings fitted. If shims are required they go betwen the bearing and the crank web (shim thickness selected to provide correct endfloat and centrality of conrods in the bores). The timing side ball is a sliding fit, as it is clamped to the shaft, so that comes off easily, The driveside roller inner is an interference fit on the crank so bear in mind not to damage it if you need to remove it to fit a shim. Hopefully (like mine) the endfloat with new bearings will be close to that with the old bearings so you will have a good idea of the shims required before fitting the new mains and therefore will not need to remove the new bearings to fit any more.

shims.