D. Crankcase / Crankshaft

The 1989 crankshaft for use in the R5k and R6k models differs from the previous year and cannot be interchanged.

The 1988 crankshaft for R2j and R4j has 24mm diameter big end pins and the centre seal and bearing is different to the 1989 model.
The 1989 crankshaft has the same bearings an seals as later model NSR250's. That is the MC21 and MC28.
It has 1mm thick thrust washers. MC21 and 28 use 1.5mm thick thrust washers with a larger OD.

The main crank webs of the 1989 crankshaft have an OD of 96mm. MC21 and 28 have crank webs with 100mm OD.
So you cannot fit MC21 and MC28 crankshafts into 1989 R5k/R6k cases.
For a 2 page diagram of the 1989 NSR250R R5k and R6k crankshaft see the attached file available for download below.
Info on the bearings and seals part numbers are listed in the drawing.

Drawings for an NSR250 MC18 R5/6k and MC21/28 crankshaft assembly jig are given here: https://www.tapatalk.com/groups/nsr250/mc18-crankshaft-3d-pdf-t232-s10.html#p5855