Updates:  Check this before doing any machining!


Casting length varies depending on the method used and other factors beyond control.  Some batches of crankcases, cylinder heads and blocks are lightly shorter than expected, and the overall bore spacing is less than the nominal 1.530", more like 1.525” (scale bore spacing would be 1.520”, but a little extra was added to give a bit more room in the cylinder block).   The main effect of this is on the crankshaft, because one made with 1.530” spacing will barely fit in a 1.525” crankcase.  Since the crankcase bearing webs can’t be moved, they determine the crankcase main bearing spacing.

Therefore, before doing anything else, measure your crankcase, decide on your bore spacing, and use it for the crankshaft.  Ideally, the same spacing should be used for the cylinder heads, blocks, and liner recesses in the crankcase, but 1.530” can be used for them.  That will mean that  most connecting rods will be slightly offset, but that should not noticeably affect engine running.  Production engines have been built with offset connecting rods.  It is not an ideal situation, obviously, but it is not a serious problem.

23apr11:  The '9305' propshaft bearing should be a 6905, and its width should be 9mm.

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