850 camshaft?

Hi, looking in my Norton 74, 850 with the cylinder off. I noticed the cam had 1/8" reliefs ground into the side of the high part of the lobes. (looks factory done, not a hack job). I had assumed this engine was stock but after looking at the cam I suspect it may be a non stock cam. Are 850 cams relieved like this or does anyone know what cam is? I know that with some high lift cams that the cases need to be ground for clearance and /or the lifters radiused. But this is the first time I have seen the cam modified.
Thank you
Bruce MacGregor

Bruce

take a look at the cam picture on Norvil's website
http://norvilmotorcycles.co.uk/ to see what a stock cam is supposed to look like. The only difference between that one and the stock cam I have is that Norvil's has a strange "rib" or ring between the two sets of lobes which may be a result of their cams being repops by a different company than the original supplier.
Scooter

I can't picture the relieving that Bruce refers to. Is a photo possible ?

I think that the ring Scooter is referring to is the boss with the through drillings for use with a timed breather where applicable. It saves having to stock two different types and doesn't affect use in a later engine.

Scooter62 said:

The only difference between that one and the stock cam I have is that Norvil's has a strange "rib" or ring between the two sets of lobes which may be a result of their cams being repops by a different company than the original supplier.
Scooter

Click to expand...

That 'rib' was a feature of the camshafts fitted to the earlier timed breather Commando models as the rib has holes drilled in it which connect to a central drilling to the breather disc. http://www.oldbritts.com/cam_bush.html

Later non-breather camshafts originally had no rib, although one shown on the Norvil website does?
http://www.norvilmotorcycle.co.uk/062608.htm

The camshaft now supplied by Andover Norton is the earlier 061084 type with breather and seems to be recommended as the standard replacement for all Commandos from 71-on (or earlier?). The Norvil website giving the info as engine number 131257-on, so it appears suitable for timed and non-timed breather arrangements?: http://www.norvilmotorcycle.co.uk/061084.htm

The 062608 option offered by Norvil only recommended for Eng No. 200000 on (maybe both types are machined from the same blank accounting for it being the breather style camshaft?).

Bruce
The Lads across the pond know their stuff and the explanation for the "rib" is spot on. BTW the 850's didn't have the rib hence my ignorance of what it was. You may want to get out a micrometer to check the lift on the cam also. I believe stock lift is about .33" so anything above that indicates a non stock cam. I'll check the width of the stock lobes when I get home tonight but as I recall they are about .5"
scooter

finally checked the width of th lobes; Exhausts are as I said about .5" but the intakes are about .56" wide for some reason.
Hope this helps.
Scooter

Bruce,

You say you have " had 1/8" reliefs ground into the side of the high part of the lobes"?

If this is on the lobe of the cam, are we talking about wear on the lobe? Some 850 cams are nortorious for being soft and the lifter can wear the lobe leaving ridges on the edge of the lobe.

Is this what you are describing?