Commando 3s cam tappet clearance

Whilst looking into hot and cold cam tappet clearance settings I discovered a significant anomaly regarding the 3s cam. -

The Norton Technical Release N3/12 "Norton 750 racer and 750 formula racer conversion kits", which uses the 3s cam, states "valves are set to a clearance of .008 in. on the inlet side and .010 in. on the exhaust (cold)".
The Norton Owners Club information states that the 3s cam uses the same .016 in ramp as the 4s cam for which the valves are set to a clearance of .016 in. for inlet and exhaust.
Both cannot be correct.

Ken Canaga said .O16 in in a previous post , and les Emery too in a file I have ....
another file just found said , 2S 8 thou and 10 thou, 3S 10 and 12 , 4S 10 and 12 ( usually this for road use , for racing it's 16 and 16 )

I've never used a 3S cam, but did run 4S cams in some of my road race engines. I got my first 4S cam when I bought an ex-NVT flat track race bike, just to get the short stroke 750 engine from it to use in my Production Racer. The engine was heavily modified, but still had its original 4S cam. When I put it in the road racer, I didn't have any specs for valve clearance, so just set them at what I had been using for my Axtell cams, .008" cold on both inlet and exhaust. I raced it that way several times with no problems. It wasn't until Brian Slark saw my PR in the race paddock (Riverside Raceway, I think), and stopped to chat that I found out what the specified clearance was. We talked a bit about Norton PRs, and I mentioned that I was running the short stroke engine from John Hately's flat track bike. I told him what I was using for valve clearance, and he advised me that the spec for the 4S cam was .016" for both intake and exhaust. I used that figure from then on, but never really noticed any difference.

From another reliable source, Mick Ofield's racing notes list the following clearances for Norton "S" camshafts:

S cam, part no. 061084, standard Commando cam, stamped "S" or nothing. - .006" in, .008" ex
SS cam, part no. 063536, stamped "SS". - .008" in., .l010" ex.
SSS cam, part no. 063761, stamped "SSS". - .016" in, .016" ex.
SSSS cam, part no. 064858, stamped "4S". - .016" in, .016: ex.

Ken

For a beginner, why do different cams have different clearances?

Mart UK said:

For a beginner, why do different cams have different clearances?

Click to expand...

Different cams can have very different opening/closing ramps, and each different ramp requires an optimum lash setting.