cb250k cb350k camshaft

[Bert Jan]

I want to know if a cb350 twin cam fits in a cb250 head and if the lobes are higher or not.

I rebuild and engine couple months back on wich the camshaft sprocket was welded on. I had to cut it up and found myself another camshaft.

Now, the problem is that the rocker arms have play, no matter how i turn the rocker arm pin.
How is that possible? To my knowledge, the maximum space between valve and rockerarm is about 0.05 inlet and 0.08 outlet. I'm getting 5mm spaces here with the pins adjusted as much as possible.

Not getting it. anybody chime in?

 

[Green199]

Pretty sure they are the same. I have a CB250 B4 (K4???) and bought a cb350 skinny cam and it fits. Ofcourse, they could have been wrong about the bike it came from.

The stock 250 rocker arms I have have 312 stamped on them I think, which makes them the same as the 350?

Have you checked you have the right rockers and rocker box for the camshaft? (can tell by the 286 or 312 markings).

 

[Bert Jan]

Hi Green, thanks for the reply! I dont have the bike here atm, but will check asap. Are the 350 rocker arms different then the 250? It looks like i'm missing 5mm on one side.. Again, will check and report asap!

 

[Green199]

Hi Green, thanks for the reply! I dont have the bike here atm, but will check asap. Are the 350 rocker arms different then the 250? It looks like i'm missing 5mm on one side.. Again, will check and report asap!

I think the entire cam/valve assembly is the same, though i'm not 100% certain. I think that between both models, the only difference is if you have the fat cam or the skinny cam. They each have there own set of rockers and cambox.

 

[Bons]

On my gf's account, Bert Jan here

So, i figured that my cam and rockers were not gonna work, so i got myself a donor engine. The donor had 312 rockers and a higher lift cam. It appears that there was a 286 cam with corresponding rockers at one time. No one knows why, but the 312 and 286 parts obviously don't work together.

I now have a 312 cam, 312 rockers and a 286 timing advance plate. Sucks. Strange thing is 3 of the 4 valves are easy to adjust to 0.05 and 0.08 but the 4th valve has about no play, like 0.01 at most. All my rocker axles are ok. i changed them out but the problem persisted on the valve. I even changed rockers, to no avail. I want to know if there is a 312 advancer plate or if the 286 is ok. Bike won't rev over 6000, even in neutral.
I guess ignition timing is not ok, as it does the same in every gear. Gonna do a compression test tomorrow just to be sure valves are ok. Cleaned carbs ultrasonic, but that didn't help either. One more thing is that the cam chain is hella tight, even with the spanner off the engine. Can barely get the camshaft gear in/on the chain. Is that ok?