Norris Cam and Regrind Questions

[freefly103]

I have a Combat cam lying around if you want to go down that path...

 

[comnoz]

Either cam would make a good core for a Webcam exchange.

Most old Norris cams are very soft -but make a good core.

 

[ILLF8ED]

It would be interesting to see where they got their specs from.

If you mean the specs I listed for Norris RX, I have a photo copy of Norris spec sheet that comes with the camshaft. The note is lift at the valve at .006 intake and .008 exhaust tappet clearance. The rocker ratio for Commando is 1.13:1. Cam lobe lift would be .375/.376. Duration 316 degrees with 108 degrees overlap.

 

[swooshdave]

Many people do.

And how do they do? I always assumed that cam like being spun more that the 850 likes to spin.

 

[ILLF8ED]

A

And how do they do? I always assumed that cam like being spun more that the 850 likes to spin.

Actually the Norris RX didn't work out so went to a combat cam. That's another several year story trying to get it to work. In the short time I used the Norris is was soft as someone else mentioned above and there was pitting on one of the lobes. I would get it welded up and reground, but there is some pitting on the end journal also. Too much work.

 

[swooshdave]

A

Actually the Norris RX didn't work out so went to a combat cam. That's another several year story trying to get it to work. In the short time I used the Norris is was soft as someone else mentioned above and there was pitting on one of the lobes. I would get it welded up and reground, but there is some pitting on the end journal also. Too much work.

So did you get the Combat cam sorted or did you go with something else? Or wish you had?

 

[WZ507]

And how do they do? I always assumed that cam like being spun more that the 850 likes to spin.

You can see from the plot that the 2S and the PW3 are essentially the same cam (as is the JS2 which is not shown in the graph). If you troll through past threads on the subject, polling owners regarding favorite cams, you’ll get such a wide range of opinions on suitable cams that literally any Commando cam offered happens to be someone’s favorite, and exhibits no bad manners no matter how peaky it is or how much lower end torque is sacrificed. The 2 cams cited above, and even larger cams have been installed in myriad stock engines and people testify that they work great, in spite of intuition suggesting otherwise. I believe the bottom line is that different riders have widely diverging opinions regarding how a given cam is performing in a given application.

 

[swooshdave]

But that plot doesn't show that the pointy cam won't actually work with a flat lifter?

 

[o0norton0o]

But that plot doesn't show that the pointy cam won't actually work with a flat lifter?

The explanation of why the plot of the pointy cam looks reasonably close to other cams, but is actually NOT close, is in the explanation that was given with the graph...

With respect to the shape of the nose we must bear in mind that there is essentially no data up there, as we have 2 data points at 0.300” lift (one on the opening side and one on the closing side) and 1 data point at the nose (0.381” lift), and nothing in between so we are relying on XL to fit a curve to 3 data points which is about as unreliable as could possibly be. Thus we really can’t say anything about what’s going on from 0.300” lift to the nose.


Thought the above might be of interest to someone curious about the pointy regrind and its accompanying timing card.

IF there was more plot data points collected near the peak of the cam, the plot of the pointy cam would make an abrupt turn at full lift. I'm sure that would create all kinds of issues with excessive wear focused at the "point" as well as high valve spring pressures being required to keep the lifter from becoming airborne.... but that's just my guess. I'd love to hear one of the more expert people here give their opinion of that pointy cam.

 

[WZ507]

The explanation of why the plot of the pointy cam looks reasonably close to other cams, but is actually NOT close, is in the explanation that was given with the graph...

IF there was more plot data points collected near the peak of the cam, the plot of the pointy cam would make an abrupt turn at full lift. I'm sure that would create all kinds of issues with excessive wear focused at the "point" as well as high valve spring pressures being required to keep the lifter from becoming airborne.... but that's just my guess. I'd love to hear one of the more expert people here give their opinion of that pointy cam.

Although the nose of the cam is clearly an issue and the subject of the above clarification (thank you oOnortonOo) the other critical feature of the mystery cam that stands out is the velocity on the flank (the steeper slope of the mystery cam relative to the 2S/PW3) which make it a real outlier, as the higher velocity and accompanying acceleration will convey harsh valve motion relative to traditional Norton cams. I think it would be scary to see that cam run on Comnoz’ spintron.

 

[Hortons Norton]

I dig seeing the spintron, I can't see the future but I can see that cam at 7,500 rpm would be fun.

 

[swooshdave]

What happens to the graph if it’s not aligned? Won’t that illustrate the real differences between the cams?

 

[comnoz]

What happens to the graph if it’s not aligned? Won’t that illustrate the real differences between the cams?

As a general rule the larger the lobes, the wider will be the lobe separation.

This is dictated by the fact that large lobes with tight lobe centers will cause the valves to tangle.

You can get around this rule by using a cam with faster lift rates and less duration -of course that limits the revs and is harder on the valve train.

Or you can sink the valves -which hurts the flow.

Wide lobe centers generally move the torque peak higher and take more away from the midrange.

Tight lobe centers [like a stock cam] move the torque peak toward the midrange and generally produce a narrower powerband. They flatten out up in the high rpm area.

PS, I have not found a cam that produces more power in the 4500 to 5000 range than a stock cam or a cam with near stock timing. They are just the ticket for street use.

 

[ILLF8ED]

So did you get the Combat cam sorted or did you go with something else? Or wish you had?

Actually I did get the combat cam sorted. Turns out the timing dot on the camshaft was in the wrong place and using the normal 10 links between the pinion and cam sprocket gave 15 degrees retarded. That’s one tooth shift between the pinion and crank gears to correct. Cam timing was pretty much right on after that and the engine pulls like a combat should now. I struggled for a few years due to this. The camshaft is an original Norton part so I wonder if others have run into this.

 

[SteveA]

Actually I did get the combat cam sorted. Turns out the timing dot on the camshaft was in the wrong place and using the normal 10 links between the pinion and cam sprocket gave 15 degrees retarded. That’s one tooth shift between the pinion and crank gears to correct. Cam timing was pretty much right on after that and the engine pulls like a combat should now. I struggled for a few years due to this. The camshaft is an original Norton part so I wonder if others have run into this.

There is no timing dot on the camshaft!

So do you mean that the timing dot on the camshaft sprocket was in the wrong place?

Or that the keyway in the camshaft sprocket was in the wrong place, which is about the same thing, even if it is unlikely to be exactly one tooth wrong!

Or are you saying the woodruff key slot on the cam was in the wrong place?

 

[comnoz]

But that plot doesn't show that the pointy cam won't actually work with a flat lifter?

Using a radiused lifter on a cam designed for a flat lifter would increase the acceleration up to and away from maximum lift. It would show a severe point on the graph.

If you test a cam that is designed for a radiused lifter using a flat lifter it would not show a pointy peak but instead would show a high acceleration rate up to near max lift and then a lot of dwell near full lift followed by a rapid drop back to the seat.

IE, Your cam was obviously designed for a flat lifter.

 

[ILLF8ED]

There is no timing dot on the camshaft!

So do you mean that the timing dot on the camshaft sprocket was in the wrong place?

Or that the keyway in the camshaft sprocket was in the wrong place, which is about the same thing, even if it is unlikely to be exactly one tooth wrong!

Or are you saying the woodruff key slot on the cam was in the wrong place?

You are right the keyway on the camshaft. Can’t say why, but rotating the crank to intermediate gears by one tooth solved the problem. Confirmed with travel dial/degree wheel for correct cam timing.

 

[worntorn]

Here's a cam I purchased that was advertised as " new old stock 850 MK3 cam, nitrided" just to show the standard profile.
The other photo is a computer designed full race Vincent cam, made to work with curved followers. About as far from Dave's pointy cam as one can get!

Glen

 

[Ron L]

Many people do.

I have a 2S in my '74 850 Interstate that is otherwise stock. Runs fine, good freeway power with a 22 tooth gearbox sprocket. A little sluggish at low rpm compared to my 19 tooth 750's, but quite tolerable.

 

[gortnipper]

I have a 2S in my '74 850 Interstate that is otherwise stock. Runs fine, good freeway power with a 22 tooth gearbox sprocket. A little sluggish at low rpm compared to my 19 tooth 750's, but quite tolerable.

Well, that sluggishness has nothing to do with the 2s cam.