Major camshaft help needed!!! - CB250 k4

Green199

Green199

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Hi guys

I recently replaced my camshaft as the old one had snapped a lug for the mounting bolt (had a crack and it failed during assembly).

So, I bought a new one and went to install it. I rotated the rotor to the LT mark, and dropped the cam sprocket slightly so the chain came off of the bottom sprocket. Then rotated so the line on the sprocket was horizontal. And bolted it to the camshaft with the advancer lobe facing up.
Put the first cam bolt in, put the 2 outer cam bearing holder covers on, and then put the tensioner on. Released the tensioner bolt so it took up slack, then retightened. Rotated the crank so I could put the other cam bolt in. All seemed good. Everything was lined up correct,y and was tight.

But everytime I rotate the crank to check its all fine (rotate 2 full rotations and check timing marks), they seem to be a tooth ahead. Everytime. So I can only rotate it about 3 times before Im hitting valves on pistons.

It doesnt physically skip a tooth off of either of the sprockets, well...im pretty sure it doesnt anyway. So I have no idea what the hell is going on!

Can anybody chime in?

Cheers, Charlie.


Edit -

Just to add more info, it has a skinny cam (will check any stamps or marking etc tomorrow)....312 rockers, and a cam sprocket with 312 on too. DID Endless camchain.
 
I know I had a "similar" issue with a '69 CB350 "fat" cam that I swapped out for a later "performance" camshaft and I left the early "fat cam" rocker arms installed, turns out somewhere around '72 the changed the rocker profile and cam base circle a small amount, the small difference made my valves and cam bind up after a rotation or two. Do some research on the different years of the engine and see if there is a similar difference (not really familiar with the CB200s.)

I know Teazer, CrazyPJ and Texasstar all seem to have quite a bit of information on the CB200s from the comments and build they have listed on DTT. Hope that helps you.
 
How many teeth on the original cam sprocket and how many on the replacement? Sounds like one is 32 and the other is 30 or 34.
 
I can't find any where online or in a manual that says the part number and how many teeth.

Ill count how many teeth are on mine when I pop down to the garage tomorrow, but I know its the same as on the one I took off.

They both have '312' stamped on them, as do all of the rocker arms...and Im running a skinny cam, with '5', 'E', '9' and 'I' stamped on it. As I am aware, I have the right rockers, cam, and cam sprocket...Im fairly sure the cam chain is the right length too, but Ill double check.

I currently have the top end completely torn down to extract a sheared bolt that connects the head to the cyclinders (by the spark plug hole), so I can easily check parts now they are apart.
 
The 2 cam sprockets I have are 34 tooth ones, and both the same. Not sure if they are the stock units or even have the stock umber of teeth. Trying to check now.

And just to clarify its a CB250, not a 200. Not sure if this would change much anyway.
 
Yeah, but its the same as the other one I have.

The engine hasn't actually run since I have owned the bike, so I cant just put it back into the working configuration.
 
so the new sprocket and original sprocket have the same number of teeth? if so that could explain why the original cam bolt was sheared off, it may also indicate other severe engine damage. maybe the p.o. attempted a cam replacement and instead built a parts bike.
 
Yep, same number. (34)

I got the motor a while ago, stripped it down fully, honed cylinders etc...split the cases...cleaned and rebuilt the bottom end.

Then assembled the top end.

The cam lobe had a slight crack in it (missed it during inspection), and when assembling after a full rebuild it luckily broke off then as opposed to it when running.

Hence the replacement cam. But I have all the correct parts in the top end.

It just seems to have the wrong sprocket ratios.
 
seems like you need to look at the crank and count the number of teeth on the bottom sprocket... no other way to be sure at this point
 
Yeah im going to double triple check the teeth on the crank tonight. I know its the correct crank, and all the teeth are in decent condition, but Ill make sure.

Could the tensioner cause a proplem with the timing?
 
Not really Roc.

Ive torn the motor down fully to inspect parts, and as of yet, can see nothing wrong with it. So im waiting for my gaskets to arrive and then im going to reassemble it and see whats up. Plus Ive got a sheared bolt to fix now....too much beer and anger do not go well with engine builds haha

Do you know if incorrectly tensioning the cam chain could lead to it affecting the timing? I know there is a factory method to do it (something like 10 degrees ATDC if I remember right), im just not sure how much this could change it.
 
having the cam chain a little loose will not cause the piston to hit valves
how does the lift of the new cam compare to the old one ? same lift ?
 
Green199 said:
Not really Roc.

Ive torn the motor down fully to inspect parts, and as of yet, can see nothing wrong with it. So im waiting for my gaskets to arrive and then im going to reassemble it and see whats up. Plus Ive got a sheared bolt to fix now....too much beer and anger do not go well with engine builds haha

Do you know if incorrectly tensioning the cam chain could lead to it affecting the timing? I know there is a factory method to do it (something like 10 degrees ATDC if I remember right), im just not sure how much this could change it.
Click to expand...

how many teeth were on the crank sprocket?
 
Green199 said:
Do you know if incorrectly tensioning the cam chain could lead to it affecting the timing? I know there is a factory method to do it (something like 10 degrees ATDC if I remember right), im just not sure how much this could change it.
Click to expand...

YES
If you didn't have the front run tight the timing WILL be at least 5 degrees out and could easily be 10 degrees off
crank sprocket is 17 teeth?
You set cam timing AT TDC, no idea where you got 10 degrees ATDC? (measuring valve opening points is a completely different thing)
 
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