Odd top end noise

raithe · Post by **raithe** » Tue Jul 16, 2013 7:26 pm

So I found a donor 67 CB77 to complete my 64 with. The motor seems to be in good shape, but when rolling it slow by hand to check valve gap and timing I noticed something strange. As the advance marks (double slash) passes the pointer there is an audible "click". If I touch the exhaust rocker I can feel it, but I see no noticeable delay in valve movement. I'm not certain its the valves but it is definitely in that region. The only other thing I can think of is the cam chain. It happens like clockwork, even if you roll back a few degrees and then forward again. Anyone have any thoughts on this?

conbs · Post by **conbs** » Wed Jul 17, 2013 8:40 am

Search this site. I think someone had this same thing happen and IIRC it was something in the advance mechanism.

raithe · Post by **raithe** » Wed Jul 17, 2013 4:56 pm

I think I saw that, about the neoprene bits on the advance unit.
A bit more investigation with a stethoscope shows it is definitely the valves, each one shuts with an audible "click". You can feel it if you place your finger on the rocker. I presume these valve systems run quiet normally? (I have little experience with these bikes)

The valve clearance is dead on.

conbs · Post by **conbs** » Wed Jul 17, 2013 6:16 pm

Hahnda has a post on "sloppy cam splines". Check that out.

raithe · Post by **raithe** » Wed Jul 17, 2013 7:50 pm

Interesting, though his showed the noise when the valves reached the max opening and this is as they close, still worth checking when I pull the head.

mike in idaho · Post by **mike in idaho** » Thu Jul 18, 2013 4:33 am

Might be some slack in the timing chain. As the rocker goes over the top of the lobe, the spring pressure causes the cam to jump ahead a few degrees.Watch the end of the points cam to see if there's unusual movement when the click sound occurs.

conbs · Post by **conbs** » Thu Jul 18, 2013 10:46 am

Mike may be onto something. There are some things that we don't know.

How many times to you hear the click in 2 complete revolutions (1 complete run of all 4 cycles)? That should help determine if it is one or both exhaust valves. Since it is a 360 degree engine it would make sense there would have be two "dead" spots (if there is one) where there is not tension on the cam chain (if that is the cause0 but I don't know for sure. If it only clicks once that would seems to indicate something in one cylinder.

If that is not it, then it would seem to have to be one cylinder's valve/guide, tappet/shaft or a cam issue like the spline problem that Hahnda had. It might be a good idea to get some good video of what it is doing before you take it apart in case it turns out to be something totally different and you would want to verify what you find when it is disassembled.

Hope that helps.

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Odd top end noise

Odd top end noise

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