The ’05 Honda crankshaft will fit in the Honda ’01 cases. It has a slightly larger O/D than the ’01 crank and sometimes (most times!) it is necessary to relieve the cases a little at around the 10 and 2 O’clock positions. The way to check this is to install the crank into each crankcase half in turn, fit the piston and cylinder and rotate the crank with the case laid horiziontally on the bench. You will see any positions where the big-end eye comes close or contacts the case and you can mark these areas for relief before final assembly.
Generally the ’05 crank will be closer to the casings anyway, so if a big-end fails it is 99.5% going to damage/crack the casings.
Another way to do this is to machine the flywheel circles and linish the big end eye O/D, but this really requires disassembly and reassembly, so would add to your cost.
The reduction in crankcase volume will generally help low end power and into the midrange, but will restrict the over-rev. The advantages of the ’05 crankshaft are:
1. You get rid of the tin shrouds
2. A stronger big end (25mm pin)
3. They are easier to rebuild/true/adjust the balance factor
My experience with the Wiseco/Hot Rods Taiwanese manufactured replacement ’01 crankshaft, is that it can be supplied outside of tolerance and is harder to correct (due to the tin shrouds). Also that the tin shrouds can crack and peel off in less than a seasons use in a Superkart application.
It is possible for the ’01 crankshaft to be rebuilt by a competent engineer with the correct equipment. When doing this I would recommend the Pro-X rod kits. But make sure the guy knows what he is doing and is used to working with the Honda tin-shrouded cranks. Get him to guarantee what tolerance he will work to and if possible check it before assembly. In Superkart use, our recommendation is, Season 1 new crank, season 2 rebuild, season 3 new crank, etc.