Motorcycle Repair: 75 honda xl250 head

Question
Hi Bill,  I bought a 75 honda xl250 with a bad head and cam everything else is mint.  I bought a gasket kit and head and cam on ebay and they don't fit.  The inside diameter of the head gasket off the bike is 83mm and the head I bought is too small.  The gasket from the kit I bought is 75mm.  The piston and cylinder look brand new.  I can't get any history from previous owner.  Can a 350 cylinder and head be retofitted to a 250 bottom end?  Do you know where I might source information on diameters and what size engine they fit.  Thanks for any help you can give, Joseph

Answer
Joseph, it looks like the STD bore on an XL250 is 74mm, which is why the gasket was 75mm to account for the 1.00 over-sized pistons that Honda offered.

http://www.motorcyclespecs.co.za/model/Honda/honda_xl250%2073.htm

http://www.motorcyclespecs.co.za/model/Honda/honda_XL350%2076.htm

http://www.xlintperformance.com/ for more specifics.

http://www.oldrice.com/xl_page.htm

http://www.wiseco.com/Catalogs/Powersports/HondaCycleDirt.pdf

You might want to check your engine numbers to be sure that someone didn't wedge an XL350 motor into your chassis, otherwise it sounds like some serious machine work was done to your motor in the past. I haven't done any work on the XL-series bikes, so am not sure if the whole top end from an XL350 will drop onto an XL250, but the engine architectures are similar.

Bill Silver