Hello all - working on a '72 cb750 motor. About 400 leak-free miles after a rebuild, it began to leak from the valve cover, then began to burn oil. The motor needed to come out anyway (found a better transmission - fourth gear was getting worn and would slip into neutral) so flipped the motor upside down and replaced the tranny with one in better shape. I flipped the motor back over and now have the cam & towers off.
My 1st question is this...If you're suspecting an oil leak coming from the rubber pucks, are there any tell tale signs from which one it is, once you have the cam towers off?
2nd question...Is there any way to identify the cam, going by the casting numbers?
last question...on the final (sprocket) drive shaft/sprocket holder, is there any gauge to go by for wear on the splines/retaining plate? On most other bikes I've worked on there's always been a spacer in between the sprocket and the shaft, held on by a nut & lock washer at the end of the shaft. On the cb750 there's a retaining plate with two holes that turns then is held by two bolts into the sprocket itself.
Thanks for your time.
The puck leaks: try to follow the source direction of the oil. Most of the time, the outer ones leak before the inner ones, because of the more stable inner section of the head and the slower cool-down in the inner portions nearer the camchain tunnel. That's not to say they are not all leaking, though, if they were not new, or if they were some of the aftermarket ones like I had last Spring (too thin). For a little while there, I got some outside of gasket kits that had a too-thin lip on the outside edge, compared to the OEM types. The last ones I got in September seem to be better, now.
If yours are new, try adding a bead of Permatex non-hardening sealant around their edge, then wipe the ooze off the top side after you press them into place. On my 750, I still have the OEM ones from the 1980 top-end job I did (over 90k miles ago), and they don't leak a bit. The cam cover GASKET leaks because of hail hitting and cracking it in a freaky storm we had, but the pucks are still fine.
The casting number question: no. They were mold numbers, shared by the 2 engine building plants. The simplest way to check the cams is to measure the lift on the intake lobe(s), as they wear the fastest (more lift on them), and see what the number is: the K0/K1 early cams had 7.8mm lift or so, while the K2 had about 7.6mm. The late K3 was sometimes down to under 7.4mm. The F2/K7 cams have almost 8.0mm lift if young.
My 750, now at about 140k miles, has 7.44mm average across all 4 intake lobes, as an example. It was 7.65 average at 50k miles in 1980. Still tops 110 MPH easily though, pushing a Vetter fairing.
The final drive shaft: on the K0-K6 bikes, they are hard as nails. The sprockets are much softer, which is this particular design approach. The lube from the chain (don't use O-ring chinas on these bikes, for this reason) lubes the splines. Mine has barely-perceptible wear marks on it, even now, and I have worn out 8 countersprockets in these 41 years with it. My current "9th sprocket" is a pair of 17 and 18 tooth units that I switch back and forth, depending on whether I am commuting mostly, or going touring.
