JIMS, crankcase lap tool

Used to lap pinion bearing race in the right crankcase. Removes more material in less time but with greater accuracy than a conventional lap. The JIMS case lap is guided on both sides of the pinion bearing race. This additional support on the cam gear side of the bearing race is achieved by means of a bolt on the base plate that precisely locates a drill bushing in which the lap turns. This base plate is located on the same engine case pins as the cam cover. The positioning of this drill bushing is held within .0002" to the engine case pins and within .0002" of the case centerline.
Now, instead of guiding only from the left side with Timken bearings, which are a floating fit, the JIMS case lap uses a special ground bearing sleeve to hold the left side of the lapping shaft without movement. Both ends of the lap are supported precisely in the same centerline as the flywheel assembly.
With this extreme rigid arrangement it is possible to power the lap with a low speed drill motor without fear of chatter in the lapped bearing race. The JIMS lap can still be powered by the conventional hand crank when desired. It is recommended to use JIMS 978341 (snap ring installer & remover tool), especially on 90-99 crankcases.
Note: See 978412 vor the replacement 1-3/4" O.D. lap head