CB72 CAMSHAFT

[joken120]

HI Guys, Can anyone tell me if I can use a CB77 camshaft in my CB72 engine ?
The reason I ask is because I may have inadvertedly put the wrong camshaft in and the bike is having non of it, not even attempting to fire. I have checked and double checked the valve timing and have had the engine out for the third time. please help as it's a bit of a faff keep pulling the engine out.

[AlanW]

Hi, yes the cams are the same, it sounds like you may have the ignition timing 180 degrees out. Check that the points are opening on the compression stroke.
Al.

[joken120]

Thanks for your reply Alan. Would swapping the plug leads over tell me if it's 180 out?

[DJM]

Swapping the plug leads over won't fix the problem.

What you can do is remove the contact breaker / points base plate and turn it through 180 degrees (upside down) and then put it back on. Reset the ignition timing and then see if it will run, the wiring will probably stop you getting the cover back on nicely but at least you'll know where the problem is or isn't.

Don't ask how I know this but it's a mistake that you should only make once!

[joken120]

I think I know where I've gone wrong here, after looking through some old posts, It looks like I have set the rotor to "T" but set the camshaft with the pointer on the points cam pointing down instead of up ...... do you think this is the reason for all my woes ??

[DJM]

Yes!

Turning the base plate over will have the same effect as putting in the points drive shaft correctly when you built the engine.

Length of wires may stop you leaving it that way as a permanent solution but if the engine now starts and runs you will know where you went wrong.

If you can sort out the wires and fit the points cover on OK there's no reason why you can't leave it like that.

Be sure to let us all know how you get on,

Good Luck,

DJM

[joken120]

EUREKA ! Finally after 25yrs, she runs. I took the engine out this morning (again) and tapped the offside cam assembly out a little bit until I could uncouple the points cam shaft and rotate it 180 degrees and tap back in again and put the top end together again. Retimed everything and bingo started absolutely great after a couple of kicks and has settled down with a nice smooth tickover. All in all it's been a good day and my age related number (1966) arrived this morning from the nice people at DVLA. I'll have to wait until the snow clears before I can do a proper road test. Anyway guys thanks a million for getting me on the right track