Honda Twins banner

1 - 6 of 6 Posts

·
Registered
Joined
·
150 Posts
Discussion Starter #1
Hi all.

I have a 1968 CB250 supersports.

I was just wondering if it would be possible for me to install a 350 top end (eg cylinders. pistons, cylinder head etc)

Was the 350 crankshaft any different from the 250? will it be fine, or will it result in mass vibrations?

is the 350 combustion chambers even any different?

Thanks for any help.

Tom in Australia.
 

·
Registered
Joined
·
13 Posts
Hi Tom

You will have problems to get the cylinder sleeves down in upper engine case. Holes are to small. Exept from that should an 350 top end be bolt on.

Leif Arne, Norway
 

·
Registered
Joined
·
2,233 Posts
Someone on here was doing this a few years ago. It was discussed in detail. I am sure a search will find the thread. However now, I am wondering if the cylinders could be resleeved with the 350 sleeves? I know that the holes in the case can be bored out for them.
TOOLS
 

·
Registered
Joined
·
305 Posts
The crank will be fine. It has different bearings. I have a 250 crank in my 350 engine and it has been working perfectly for many 1000's of miles and more than 4 years now. I am also using a 250 head but that has to be modified to suit the cilinder. The combustion chamber is larger on the 350 but other than that, the head is identical.

To mount 350 cilinders on a 250 engine case, you'd have to enlarge the holes in the case to fit the sleeves of the 350 jugs.
 

·
Registered
Joined
·
150 Posts
Discussion Starter #5
Does anyone know if the combustion chambers in the heads are different? As if they aren't, that means i don't have the added expense of a cylinder head also. The 350 cylinder blocks are a-plenty on Fleabay.
 
1 - 6 of 6 Posts
Top