650SS and 4S camshaft

Hi George.

Thanks for the reply. Unfortunately I cannot check to see if it is a 4S without splitting the cases, because I believe they are marked on the side of a lobe. It should be, it was sold as such, but whatever, it gives high lift, so is a sports cam. It may be possible, after removing head and barrels, to get a dentist's-type mirror in to see, but I don't know if that will work.

As for setting it equally either side of tdc, that is not possible, because the duration of opening of the inlet valve with this cam is 296 degrees; opening at actually 64 deg btdc and closing at 52 deg abdc. It should actually be closing at 89 deg abdc, giving a duration of 333 degrees, so is closing 37 deg early, to be exact. This compares with the SS cam, as fitted to the Commando, which opens at 50 deg btdc and closes at 74 deg abdc; a duration of 304 deg.

With the 3S and 4S cams, the measuring is done with clearances set at .016", and left there.

This gives me an idea..... The SS cam duration is only 8 degrees in total different from my measurements. Maybe it is an SS after all, and Norvil sent me a SS instead of the 4S..... On that basis, having checked my exhaust valve readings against the SS, they are only 9 deg different. The difference in valve clearances when checking the 4S & SS could explain that.

I have a plan! Treat it as an SS...... Re-set the clearances to .013", as per the SS cam, set it up to open at 50 deg btdc and measure up. To be honest, I now don't care if it is an SS cam, not what I bought, if I can get it running right. The SS is a good cam anyway. Then re-set the clearances to .006" & .008" and try it up the road.

Thanks George! Watch this space..... it may be a few days before I get to it.

Just to clarify my previous post - when I refer to the SS cam, I mean the standard cam as fitted to all SS, 650, 750 pre engine #131257. John Hudson referred to it as the X1. This is not to be confused with the 2S, or double S, which is the Combat cam.

Update; I am waiting for a new set of pushrods, and rings, to arrive, along with gaskets, so no further progress yet.

Interesting stuff Colin. On the Norton, with the X1/2 cam, maximum lift on the inlet would be at 102 degrees atdc, the exhaust 70 abdc. I will check it tomorrow and see how that works out; good tip!

Also on the Norton, you can't measure the valve lift off the pushrod. You could calculate it by multiplying your figure by 1.13, which is the rocker ratio, but to measure directly, it is best to do so off the top of the valve spring collar with a dial gauge.

Colin. Yes, I did say that you could multiply the pushrod lift by the rocker ratio, didn't I? I was being a pedant, saying that you can't measure it by that method, but you can calculate it. Best to measure maximum lift direct, though, I would have thought, as apart from anything else, you don't need to take the head off!

I agree about manufacturing discrepancies in the cam. I believe the keyway on mine is in effect 10 degrees out to where it should be, or it could be the timing marks..... I will set it up by dialling it in, which I will do tomorrow. I will check as you suggest, at maximum lift. The lobes themselves seem to be true to each other, and consistent, by my measurements so far.

Interesting info there Fritz. The 'cam 110' and 'cam 120' are the ones I was differentiating between. The 'cam 110', the standard cam fitted to all SS & 750's, is the one I think I have, otherwise known as the X1 or 2, depending on depth of case hardening, apparently.

The 'cam 120' is the bad boy! 2S, or Combat, sometimes confusingly called SS.

Update:- Treating it as a standard SS; X2; #22729 etc cam, with clearances at .013", opening at 50 deg btdc, it closes at 70 deg abdc. Figures published by RGM in their tuning manual say it should close at 74 deg abdc; so close 'ish. Maximum lift is at 78 deg bbdc, exactly where it should be.

The exhaust opens at 72 deg bbdc, closing at 42 deg atdc. Published figures say 82 bbdc & 42 deg atdc.

Closing the clearances to zero, as you suggest, David, maximum lift on inlet is .43"; x 0.885 = .38" cam lift. Published figure is .375".

The exhaust lift is .375" x 0.885 = .333", against .346" published.

I am guessing it is the standard cam, with some machining 'tolerance'.

I am happy if it is, as the cam choice was made some time ago, and I have learned a bit since then!

The PW3 for the Dominator wasn't in stock with anyone when I bought the cam, Joe. As I said, it was some time ago.

David. I am not entirely convinced. According to the data I have, the X2 and Combat both have the same lift, but the Combat has 330 degree duration, while the X2 has 304 degrees. Mine has 300, so probably within tolerance.

I am removing the head and barrels tomorrow, so will see if there are any i.d. marks visible.

Ian

Norvil only list the normal range of camshafts; 22729, 2S, 3S, 4S, 7S for the Dominator, so it has to be one of those, not a re-grind.

I have looked at the cam which was in there when the engine got trashed, and it is an X1, marked on the un-machined circumference on the timing side of the cam lobes, along with what I assume are casting marks.

I have also looked at the cam which came out of my original Commando 750 Proddie Racer. This should be a 3S cam, but I can see no markings at all, not even on the end.

My inclination is to fit the new piston rings, remove the valves, check the springs etc, put it together and try it up the road to see how it goes.