I heard a tap, tap, tapping--and it wasn't the raven

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I finally got my 72 Combat running last night and took it out for a spin. Commandos don't take a back seat to any other bike as far as a great sounding exhaust note! While I was riding, it dawned on me that I had never heard a Commando actually fired up, although I've lusted after one since my first trip to a Norton dealer in 1969. Anyway, on to my question. The the bike starts, idles!! and runs well. Once it was warmed up I noticed a rapid tapping noise above around 2,500 rpm, which was loud enough to cause me concern. Now, that may be normal valve clatter, but I wouldn't know what normal sounds like. While holding any steady speed in any gear, the noise is really noticeable, but it disappears upon acceleration and in not noticable while at idle. Valve adjustment clearances are spot on for a Combat. I know questions about sounds are difficult to answer but I would appreciate any suggestions. Kinda sounds like tapping a pencil point on the top of a metal desk. I've spent months working on this baby and would hate to blow it up due to my ignorance. So, is it normal or abbynormal?
It would be nice if it was simply a worn alternator rotor key........
Just a thought, this is a bit hard without listening/experiencing as you have stated.

Your Raven, er, tapping sounds abnormal to me. You should check for excessive valve clearances. However, sloppy valve clearances should be audible below the 2500 RPM threshold you mentioned.

Possibly a valve guide is tightening up with an increase in head temperature? Have you had any head work done lately?


Complete speculation here, but my guess I would be piston slap....

I had a '82 CB900F with a worn wrist (gudgeon) pin that produced a similar ominous sound. I have a nice piston/con rod paper weight...

I too am in the same boat as you - I have yet to hear my bike run... (oh the shame) In theroy I have a Norton, in reality I have a bunch of parts scattered throughout the basement (sigh)
tapping noise

As you say diagnosis is pretty difficult by description. My '72 combat has what you describe. In my case it's a tappet noise probably due to the valve stem top hardening being worn or a worn valve tappet adjuster tip. I'm not worried about it since I know everything else is as it should be. Combats are probably prone to unusual valve tappet wear due to the weird angle caused when .040" was milled off the head the pushrods weren't shorted to match.
I have had a layshaft 4th gear lose a tooth and make a sound that was difficult for me to trace.

You could "nurse" the bike along at first and not hear anything. It was because the one tooth was about to break off, but hadn't quite broken off. I had to get my bike home from a couple of hundred klms away & was lucky to do so. It did break off completely after I made it home.

3 of us, all "old" norton riders couldn't pick what is was until I finally pulled the geabox apart. We had been using the screwdriver trick to try & trace the sound & thought it was coming from the alternator area.

Once I got the gearbox apart, you could see where the tooth may have been "faulty" by the fracture line.

Just another thought.
Norton Noise

nortonfan said:
It would be nice if it was simply a worn alternator rotor key........
Just a thought, this is a bit hard without listening/experiencing as you have stated.
Well I have a 71 Commando High Rider and I also was having the same sort of tap tap tap and even after adusting the valves it was still there. I pin pointed it to the left hand intake, so I decided to remove the head (which is a treat in itself) so low and behold I discover my left intake push rod was slightly bent, so I ordered a new head gasket and new push rods and now she purs like a brit kitten.
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