it is critical that the crankshaft centreline be positioned correctly in the chassis both in the vertical and horizontal planes.
A very true statement. With the 500 conversion, the effort is to get the engine level ("Honda" logo
on the clutch cover) parallel with the bottom frame rail and using different spacers at the swingarm
to lign up the countershaft with the rear sprocket.
The gen 4 conversion I am doing is a bit more comprehensive. I am replacing everything from the
"Y" to the pegs - the whole cradle - in order to gain the clearance for the exhaust flange, right side
clutch cover bolts and to gain a little more room between the head and fuel tank. This was actually
done on the gen 5 frames as Honda lowered the center of gravity 1" to improve handling. I also think
it will be a cleaner, more OEM looking conversion. I also have to deal with airbox/airboot problems.
The stock CRF airbox/airboot does not line up or reach the 500 carb. Most folks fab up some kind
of adaptor plate to mount to the airbox that allows the use of a 98/99 CR250 or other longer airboot.
Other problem areas are the lack of clearance between the fuel tank and spark plug, coil location,
radiator conversion and pipe/silencer. The gen 4 CRF250 frame is what AJ at Service Honda is currently
using for his conversions.
Compared to everything required in a gen 4 conversion, the gen 3 is a much better choice from an amount
of work viewpoint.
dogger