4S Cam.

A mate of mine who races Dommi's has a small collection of Cams and has offered me a new, still in the packet, 4s Cam
as payment for a pair of Miks that I gave him to try.
Norvill site suggests they are a broader power spread than 2s.
Has anybody here tried one, my engine is Combat.
AC.

I know nothing but did find this to entertain ya until experienced posters pipe up.

cam-timing-and-torquiest-cam-t3600.html

If you go to the Atlantic Green website Dave has a chart with the 2s - 4s comparison. The 4s has a little less overlap and makes a small improvement in the powerband. They are pretty similar otherwise. Jim

Yes Hobot that was entertaining.
Thanks Jim, Assuming the 4s is at least the equivalent of 2s, plus a little broadness, then I guess it's better.
I think my engine pulls reasonably well with the 2s, so if they both deliver about the same,
but one starts a bit earlier than the other, then it should be better... shouldn't it. ???
Better hurry up and make my mind up, because it is going back together as we speak.
AC.

The bike in this thread has a 4S cam. It is about time we ask DaveM for a report on it!

750-restoration-finished-and-ready-fire-t4928.html

Russ

I've run 4S cams in race bikes a number of times. It used to be quite popular with road racers, probably still is. The most interesting thing about the 4S is the spec for clearance. Because of the ramp design they used, Norton specified the clearance at .016", not the usual .006" - .010" range of most Commando cams. The first time I ran one, I didn't know what the clearance should be, so I set it at .008". I ran it that way with no problems for several races, until Brian Slark told me at the track that it should be .016". I reset the clearance, but could tell no difference from a rider persepctive.

Ken

I ran a 4S in my race bike for a few years and had exactly the same experience with clearances as Ken did. I didn't know what clearances to run and set it at 8 and 10 thou.

I then had a lubrication problem that damages that cam and I replaced it with an Axtel 5S. I couldn't tell the difference between them.

I'd happily run the 4S in a hot road bike.

Thanks...rvich, lcrken and pommiejohn,
Hopefully DaveM will be with us soon.
I don't know too much about overlap and lift etc, but comparing the two Cams, side by side I can see
that the 4s is a little higher but is a little broader at the bottom 1/2 as well.
I can understand, or assume, that with higher lobes, there must be more spring pressure on everything
from the Cam up.
Would I need special valve springs or not.
I am not going to ask for opinions on other Cams, there is enough info here,
but do I need valve springs with the PW3 or JM's I assume with out high lift that the originals should be ok.
A wise man once said... "Better to keep your mouth shut, and appear ignorant, than to open it and remove all doubt."
But if you don't ask, you don't find out.
Never assume.... It makes an ASS out of U and ME.
AC.

I have always used standard springs with the 4S and with the Axtel cam with no problems.

You may need to check a couple of things.
1: Valve to piston clearance, depending on your pistons, the valve cutaways may need to be enlarged.
2: Valve spring compressed length. You need to check the springs don't go coil bound when at full lift. From memory ( and someone better qualified will probably correct me) you need at least 45 thou from full lift to coil bound.

Thanks mate, or is it matey.