Topic: Swapping heads Cb650

[Hareetmanni]

Hello. So i have 2 Cb650z's both 1980. Other one has been in bits since spring 2023... I refurbished the head fully with new valve stem seals etc. Its like brand new. I want to put that head to my other Cb650 thats driveable. Can i swap the heads? The refurbishment cost me roughly 300€ so i want to put it on to the better bike. And ill get new carbs for it when i have money for it (turns out renovating an apartment is expensive)

[bryanj]

There were two different heads on the 650, one with inlet stubs bolted on one with them cast in. As long as both are the ssame you can swap them, with new gaskets of course

[Hareetmanni]

Thanks. Ill take the head off the better 650 and look if they are same. Should be. And new gasket has been bought already 

[bryanj]

The carbs were different between the two as well

[Hareetmanni]

Yep. 

[HondaMan]

There were two different heads on the 650, one with inlet stubs bolted on one with them cast in. As long as both are the ssame you can swap them, with new gaskets of course

Bryan:
Do you know when change occurred? Model, or 'type'? I'm supposing it was the 650C engine?
I don't see many of the CB650 SOHC4 bikes around here. I think I've only ever worked on 2 of them. The CX500 seems to have dominated this local market then.

[fizzlebottom]

The two different cylinder heads for the SOHC/4 CB650 run were between 79-80 and 81-82. The early 2 years had PD carbs and the later 2 years had CV carbs. These had different spacing. Since yours is from 1980, you would have to have a '79 or '80 head to make sure your current carbs would fit properly. If you used a later head and CV carbs, you'd also have to figure out an airbox solution since they're pretty specific to carb & frame combinations.

[bryanj]

The 650 was not common here either, i just remember seeing both types of head nos on a stall at a swapmeet mate

[Hareetmanni]

Both bikes are same year. Same carbs. I was thinking about the head tolerances. But i think these sohc 650's arent so picky

[bryanj]

No Honda is that picky or how would you buy spares?

[fizzlebottom]

Both bikes are same year. Same carbs. I was thinking about the head tolerances. But i think these sohc 650's arent so picky

You're fine then. Just make sure the cylinder head deck and cylinder deck are both nice and flat.

[RAFster122s]

If you don't have the equipment or Do not want to buy it and learn, then have a machine shop that does rebuilds of motors measure your head and cylinder block for flatness. The charge is usually worth knowing that you won't be having a failed refresh of the motor.