62mm crank whats required?

[peter357bikes]

Thinking of going up to a 62 mm 110 (GT) crank on my RB250, currently runs a 60mm 107 rod, as I may be getting one of the new engine cases. What else would I be needing to do and or consider...and before i am asked, what will this achieve?

[Eden]

lag double post

[Eden]

things to consider:
you will need a special 18 to 16mm little end bearing
you will need a 3.5mm packer with a gasket both sides or another packer if your planning to change the port timings
if you use a 3.5mm packer it will also be a good idea to lower the bottoms of the transfers and exhaust port by 1mm as the piston will be 1mm lower at BDC
if you choose to use a 2.5mm packer to keep the bottoms of the ports as they are you will need to either have a 1mm recess cut into your head or use a 1mm head gasket.

these packer suggestions are abviously based on using the crank in your current case, the actual amount of packing may well be slightly different on a new case but the difference between a 60/107 and a 62/110 is 5mm, 4mm higher and 1mm lower, their are many ways to accommodate the crank all depending what port timing you want to achieve but for best results you will need some work to the ports in the barrel as well. It will work with out porting work but not as much of an improvement will be gained.

send me a PM if you want to know more

[peter357bikes]

Going with the new GT case. Thanks for the info. May get the 2016 RB monoport barrel (longer), so may remove the need for large spacers. and with all the original bits I have, I can sell on the original RB block virtually complete to fund the process.