Topic: 750K2 Cam Chain Tension and ...

[The Lone Builder]

Trying hard to get to the end of the  rebuild of my CB750 K2, I was setting the tappets. So I set about adjusting the tension on the cam chain - 15deg after TDC etc. Nothing happened when I loosened the lock nut and bolt, so I removed the adjuster body.

Now as I rotate the engine the tension on the chain varies! The chain is first tight at the back, and loose at the front, of the cam sprocket. Rotate a bit until the rocker (whichever rocker) just moves off the appropriate cam and the chain "snaps" and is now tight at the front and loose at the back. Continue turning and another "snap" results in the tight back, loose front scenario and so on. Engine turns easily enough.

I can lift the chain off a tooth or two at the loose side, but not enough to walk the chain around the sprocket. At the tight side, it is tight!. The chain has about 25,000 miles on it. but was not overly stretched when I had it out.

This doesn't seem right to me, so any advice, and what I must do to fix, would be much appreciated.

A related issue is that I noticed that the end of the, new, adjuster screws do not sit flush on the top of the valve stem.

The pics show the position with the engine at TDC on 1&4. I had set the gap on the inlet side, but not the exhaust side. When I turn everything round the adjuster and valve top sit flush. Is this normal?

Thanks,

Sean

[enwri]

Cam snapping around when the chain is loose is normal. Valve springs trying to push it around.
Better check your valve timing before you go much further, may jump a tooth if you crank it around without the tensioner plunger in it.
The 15deg. thing is to get the chain to "snap tight" on the front of the chain, so as to be able to adjust out the slack on the loose side.

[The Lone Builder]

Thanks Enwri.

I seem to have fixed whatever it was. I went back to the start:
Checked cam timing - a useful note I found in Haynes says, when No 1 at TDC, base circle of  No 4 cams face up and No 1 cam in overlap position.
Retorqued the rocker centre bolt (6 ft-lb) and the cam cap bolts (8 ft-lb)
Set cam cahin tension at 15deg after TDC.
With all rockers loose everything spun round nicely with even tension on both sides of sprocket.
Adjusted the tappets.
And hopefully, now all done!!

Sean