engine rebuilding question

[not2hi]

i rebuilt my top end last year, then later found out the bottom end case half had cracked...so i bought a new bottom end assy (used) and am planning to start combining the 2 motors into 1...

my question is will i need to rebore the piston and replace the rings when i do the rebuild or is there a way i can pull the top end off intact and then just place it on the new bottom end?

Any other things to watch out for in this rebuild?

thanks in advance!

[dork]

you have to take off the rocker cover to get to the head bolts, but you might be able to slide the head and jug off togeher after that, but you risk disturbing the head gasket. its far easier and better to take it apart. depending on how much time you have on the top end, you can just replace the rings and flex hone the cylinder. if you're not splitting the cases, then its pretty basic. also check the rod on the new crank, it should have no up and down play and very little side to side play.

where did your case crack? i've cracked 2 in the same spot on 2 different bikes. it seems like they must flex in that area. 1 leaked oil, the other didn't.

[not2hi]

it's cracked at the lower front mount (where the motor attaches to the frame)...apparently at some point the rear mount bolt became loose and fell out, which put stress on the front bolt...i tried JB Weld twice to no avail...and its too close to the bolt head seat for welding. the new bottom end is complete except for the outer covers...i may try to do the top end swap as one piece...we'll see how it goes!

thanks for the help!

[TC426EX]

I would just take it apart and do it. Re hone the cylinder, get a set of new rings and thats all you would need. Put your top end on, torque everything down, adjust your valves and timing and youll be ready to go...