Topic: 1978 CB750F Cam 180-degrees out???

[blackbyrdmoto]

So, I made a stupid mistake and forgot to tighten down the lock nut on one of the valve adjustment screws. This caused me to cut the frame (install a frame kit) so I could pull the valve cover, where I found what I think is a problem. Looks to me like the cam is 180 degrees out. When #1 @ TDC - the notch is down.

The engine would run, but I was having trouble with erratic idle, high idle, and there was a noise I never quite isolated, but it didn't sound good. Could these problems be caused by the cam being installed incorrectly by the PO?

Can someone just confirm this cam is installed wrong, and that I should pull it and re-install with the notch up?

[blackbyrdmoto]

OK, so this thread leads me to believe the notch facing down is NOT a problem... http://forums.sohc4.net/index.php?topic=107248.0

[madmtnmotors]

Impossible to install cam "180 degrees out". Cam makes 1/2 turn (180 degrees) for every 360 degrees of crank rotation. Rotate the crank one full turn (360 degrees) back to the 1-4 timing mark (without disconnecting anything) and the notch on the cam will then be pointing up.

EZPZ PFM

[blackbyrdmoto]

Impossible to install cam "180 degrees out". Cam makes 1/2 turn (180 degrees) for every 360 degrees of crank rotation. Rotate the crank one full turn (360 degrees) back to the 1-4 timing mark (without disconnecting anything) and the notch on the cam will then be pointing up.

EZPZ PFM

This is true, but at that point #4 is at TDC. Apparently, though this makes no difference according to that other thread.

[Bodi]

You have a big problem if #1 and #4 are not at TDC together. What you describe is 100% normal and OK. TDC just refers to the piston position, not which stroke it's on.

[blackbyrdmoto]

You have a big problem if #1 and #4 are not at TDC together. What you describe is 100% normal and OK. TDC just refers to the piston position, not which stroke it's on.

Thanks, Bodi. I guess I was confusing piston position with which stroke it was on. Anyways, thanks for confirming it is OK as is.

Now just waiting on gasket and frame kit so I can get it back together again.


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[PeWe]

Easier to set valve lash with cover off. You'll see when rocker arm pad is on the base circle and should have correct lash. I always write 8 rings on a paper that will show each valve, check each with an X after I had adjusted and tightened direct. Rotate engine afterwards and check them all again.
No plugs in when doing this. Put rags in the plug cavities so nothing can fall in, like nuts and other nasty stuff.

[blackbyrdmoto]

Easier to set valve lash with cover off. You'll see when rocker arm pad is on the base circle and should have correct lash. I always write 8 rings on a paper that will show each valve, check each with an X after I had adjusted and tightened direct. Rotate engine afterwards and check them all again.
No plugs in when doing this. Put rags in the plug cavities so nothing can fall in, like nuts and other nasty stuff.

Thanks for the tips, PeWe. I am still learning...How does having the plugs out help?

[PeWe]

Much easier to rotate engine without plugs in. No problem to use a 23mm spanner on ignition side to rotate engine with. OK to use kick starter by hand too.

[madmtnmotors]

How does having the plugs out help?

You eliminate cylinder compression so you don't have to fight the compression stroke while turning the engine. The compression stroke gets vented out the spark plug hole.