Motorcycle Repair: Yamaha 400 Maxim, metal ruler, valve seals

Question
Hi Wayne,  I have a nice low mileage Yamaha xs400 Maxim, 1982. I am just
about to change the head gasket and was wondering if there is any thing else
I should do since the engine is apart. Second question: Is there a big bore kit
on the market for this bike? I would like to bore the cylinders to get some
more torque and power. Thank you for your time and advise! Michael.  

Answer
Michael,
always good to check or maybe lap the valves
while it's apart and check the valve guides and replace
the valve seals. Make sure the head surfaces
are flat, check with a metal ruler or similar straight
flat object. Not sure about any big bore kits,
try google. Big bore will put added strain on the
bottom end of the engine, so may reduce it's life.
Replacing cam chain/tensioner parts may be an idea too.