Just pulled the main bearings off of my Mk2 crankshaft and found 2 shims behind one of them (see pic). They are each about .040" wide.
I have posted before about my engine's oddity of having Mk 3 crankcases.
I'm wondering if the distance between the crankshaft outer webs is greater on the Mk 3 crankshaft than the Mk 2 and these shims have been put in to make up the difference.
Haven't taken the bearings out of the crankcase yet but it looks like there are shims behind one side of these as well.
Welcome any thoughts.
Crank Shims
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Mk3 crank width
Nigel, on an old Mk3 crank I have here the width measures about 152,5 mm across the cheeks. In a post on accessnorton it is said that the Mk3 crank is 3 mm wider than the Mk2 version, and that a 1,5 mm shim on either side is required to make the latter fit in Mk3 cases. Superfluous to mention that the crank is to sit centered to the cilinder bores.
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Nigel
No idea re the different crankcase widths but if the engine has been running well without minimal or excess end play for many miles, I assume the builder knew what he was doing.
The shims in your pic look good and I would record the thicknesses, which shims go where and reuse them in the current configuration with new bearings. Check the end play to verify the final result
Very important to have enough end play with around 0.010" to 0.012" on a stock 850 as recommended by both Norman White and Jim Comstock with 0.015" recommended by Jim for race motors.