Valves adjustment/wrong camshaft postion (Honda CB250G (1977))

[Justinas]

Hey there,
need a little help. After rebuilding upper part of the engine (first time for me), a problem appeared when trying to adjust the valves. When engine is turned to LT position on alternator, both valves of the left cylinder should be closed. Unfortunately, exhaust valve is opened and sometimes even touching pistons (thanks for crazypj for explaining that). Even when I unscrewed adjustment screw all out, but it still is open, because it's pushed by rocker arm. Similar things with other valves.
I clearly messed up something in assembly. The only thing I can think of is wrong camshaft postion. But I checked that three times and marks on the sprocket are horizontal when alternator rotor is in LT position (pictures from manual below). Don't know where to go from here.

Maybe anyone has any ideas where I did a mistake in assembly?

Thank you for any thought!
P.S. It's my first engine work, so a problem may be kind a self-evident (not for me naturally :/).

 

[frogman]

Re: Valves adjustment/weong camshaft postion (Honda CB250G (1977))

When you put the cam sprocket back on, did you rotate the cam CLOCKWISE to tighten the front side of the cam chain and then check the marks?

When you set the CAM you should set the Left side with the lobes DOWN into the head at LT before buttoning things up.

And if you touched the valves with the pistons there is a good chance you might have bent them.

 

[rockcitycafe]

Re: Valves adjustment/weong camshaft postion (Honda CB250G (1977))

as long as you didn't put pressure on the valves, you'll probably be fine, but if you turned the engine all the way over with valve contact you're screwed, they'll flex just a bit without bending permanently, but not that much. you almost certainly have the cam upside down, you need to think through assembly, if you're just following directions, you're probably not being careful enough, the thought process there should have been: this lobe is sticking way up, so that means this valve will be very open... would it be very open at tdc? (either at overlap or firing?) the answer would have been: no, then you should have gone back and asked questions or consulted other info sources... if you're working on motors, you're going to screw up, it's a given, but a valuable lesson you can learn is to know when you're not thinking through something enough

 

[Justinas]

Re: Valves adjustment/weong camshaft postion (Honda CB250G (1977))

Thank you guys, it's getting clearer in my head.

That's definitely the mistake I've done - not thinking about the hole principle and just blindly following the manual. One mistake and I'm screwed. Ok, this is now learned and I will not forget that in the future :]
Tomorrow will check and probably turn cam shaft to right position. I guess i should check if they are flexed using valve leak test?

http://www.youtube.com/watch?v=ubtdUYUNvYQ

 

[crazypj]

Re: Valves adjustment/weong camshaft postion (Honda CB250G (1977))

CB250 wouldn't be a 77 unless it sat in a dealers for a few years?

Should be a CJ
Anyway, you can use all the information for a CB360, the major difference is the bore size (56 vs 67)
Also, the cam turns at half crank speed (2:1 rotation)
At TDC cam lobes can be up or down, depends if it's TDC or TDCC (compression)

 

[Justinas]

Thank you guys, the camshaft was really in wrong position. To make sure everything is ok with valves, decided to renew heads too. This time I'll reassemble everything with a little more thought. Hope to have engine up and running in few weeks.

Thank you again!

 

[crazypj]

That isn't the way to check for leaks, fill the port, not the combustion chamber :

 

[Justinas]

That isn't the way to check for leaks, fill the port, not the combustion chamber :

Don't worry, that's what I did. Realized, that maybe this video is better :]

http://www.youtube.com/watch?v=DDqN0XpapMo