[ashimotok0]

Hi I have two spare CB250K heads for my bikes one of which has suffered interesting trauma at some point (no history of engine it came from). I have been asked what the differences are between a CB250K head and a CB350K one. They definitely have different ---286---- and ----287--- part numbers in my 1969 Parts book. The valve part numbers are the same for both models though. Anyone know the differences please? The Picture is of the CB250 (K4 I believe) one with 'trauma'. Anyone knowthe differences between 250 & 350 K heads?

 

[ashimotok0]

Anyone have any thoughts advice on this please?


Cheers ... Ash

 

[Yendor]

I would think the difference would be in the Combustion Chamber dimensions/volume.

From what I know the 250 was built on the basic 350 motor with a different bore diameter (not sure if the stoke was different but could be).

 

[ashimotok0]

I am beginning to suspect that the head pictured is in fact a 350K one not a 250k..... I am going to my 'stash' tonight to dig out what I know is deffo a CB250UK one from a 5k mile bike.

 

[ashimotok0]

Well I cocked that one up. My head picture I posted was from a Cb350K1 and I think I know what the cause of the trauma on it was. I got the bike from DK (a large importer in the UK of classic bikes, mainly from the USA) with 10k miles but with weather seized engine. When I stripped it the engine was in really nice condition (inc cam and followers) but surprisingly had +0.25mm 1st overbore genuine Honda pistons. The engine was not in fact weather seized...I found a large mangled split pin jamming the primary drive gears.


This picture below is deffo a CB250K0 head that was taken from a 1969 Reg. left in a garden to rust with only just less than 6k miles on it that I 'found' end of last year. Note the lack of chamfer compared with the two CB350 pics. of heads. I reckon that the chamfer is the difference between 250 & 350K heads. I did have a CB250K2 with Read Titan (a old 60's/70's UK bike specialist) 325cc conversion in the 70's though which used the CB250K head and special Hepolite pistons & rings.