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Motorcycle Repair/75 honda xl250 head


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

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. for more specifics.

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  

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Bill Silver


Need help with vintage Hondas from the 1960s? I am an expert with 250-305cc bikes in particular and most all of the other pre-91 models, in general. I do NOT claim to have a great deal of experience on Gold Wings, Cruisers, ATC/ATVs and dirt bikes.


I have owned/ridden/maintained Honda motorcycles for 35 years. I have written five books on Honda repairs and collecting. I was a service manager for two Honda shops back in the 1980s.

VJMC (Vintage Japanese Motorcycle Club) of North America

VJMC newsletter, as editor for two years and as contributing editor currently.

3 years auto shop in high school, teacher's aide in Automotive Technology in Jr. College, Diesel mechanic course in college, self-taught mechanic and automotive writer.

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