IDENTICAL TWINS?

PART TWO: BEGINNING THE BUILD

Remember the Grand Plan whereby I would fit the complete roller crank into the Austrian cases and then assemble all the other bits on top? Well, the Austrian cases are exactly ¼” wider between the main bearings than the roller crank! No way of fixing that without changing other things to suit. Plan B is thus to use the plain bearing crank – which exactly fits the cases – in this build.

Measuring the one plain big end rod shows that it’s 6.00” centres, 9/16” shorter than the ‘roller’ steel rods. Measuring the stroke of both crankshafts shows that the ‘roller’ one is exactly 77.00mm whereas the plain bearing one is 73.50mm. A close look at the cylinder bores showed a slight lip at the top of both and score part-way down one, enough to merit an oversize rebore on the standard 64.00mm.

Plan A was to use Triumph T100 pistons, +.060” oversize, which would give a bore diameter of 64.50mm, enough to clean up the cylinder bores. However, this