Originally Posted by focallength
I havent heard any negative on a BB kit, however the very nature reduces longevity. Im slightly concerned with the head bolts. I had a xr600 with a 660 BB kit (10% over bore same as a 400 to 440) and it pulled the head off.
The big suck with my bike is I need a new head, thats $600 for a blank head. Im not reusing any parts from the seized head.
By rebuild I mean the kits they sell on line, theyre mostly bearings and gaskets, top end comes with a new piston...I dont think I need to go hog wild on a head, nothing fancy just stock parts aside from cams.
I assume that you're looking at a brand new core. The only other OEM internal parts that you'll need are cotters and tappets which will cost about $240. Ferrea valves are about $120 and springs with retainers about $100 (Ferrea, APE or Kibblewhite)... That covers the bulk of it. The OEM stuff is about the same total price so is not unreasonably priced, but you can do better. I'd use at least Ferrea valves.
The head is bolted through the cylinder to the crankcase...Lifting the head due to the cylinder is improbably.
One point in favour of the stock bore is that the OEM piston skirts are longer and wider than the non genuine parts including those for the standard bore and there might be a longevity advantage using an OEM piston.
I don't think that there is a problem with using a 94mm bore, but if using the stock bits makes you comfortable then go for it. The S motor only needs cams, carb, compression and exhaust to go from asthmatic to a nice motor. Big bores are optional.
BTW, I'd definitely want to check the crank and transmission very carefully because it seems from the cylinder that the damage may not have been limited to just the head.