Reason Norton cams wear?

Gents, and especially the Norton boffins,

I was looking at the cam and followers out of my Commando today. And something struck me...

I know the followers are 'flat' in the horizontal plane, but they are half round in the vertical plane...

It seems to me, that due to their half round design, when the cam lobe rises to meet the follower, it is always met by a sharp edge. And that this sharp edge could easily have the effect of scraping away the surface oil on the cam lobe, leading to metal to metal contact. Operating in such a way would also partly explain why Norton's seems to benefit form oils high in Zinc.

A large enough flat follower (that is not half round) will always present a smooth surface to the cam lobe as it rises, as will a radisused follower. Moreover, with radiused followers, when the cam lobe rises, there are actually 2 radiuses meeting, in this case they probably create a 'wedge' of oil, ensuring that there is always oil twixt cam and follower.

Well, that's how it seemed to me today, and of course, I could totally have the wrong end of the stick (again)! So I would be interested to hear from the knowledgable ones...

Actually the cam should never contact the edge of the lifter. The wear pattern tells the tale.

If you use early design lifters with the beveled edges and a race cam -the cam may contact the edge where the bevel starts. If it does they will not last long.

comnoz said:

Actually the cam should never contact the edge of the lifter. The wear pattern tells the tale.

If you use early design lifters with the beveled edges and a race cam -the cam may contact the edge where the bevel starts. If it does they will not last long.

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I thought the wear pattern was caused by the 'edge'...?

On valve train that does not snag edges breaking oil layer - its purly the time with and w/o oil surfing that wears lobes and lifters. Dry sump starts can be proven to be the worst wear state of all and reason past Nortons meant for every day go to work and back economical endurance had cam bath and other really expensive engines have pre-oilers. Ludwig has seen the wisdom to make his own cam dam so not just humble hobot opinion. Peel has provision to pressurize oil before starts to fill crank and flush to head before starts but not sure if I will install or not til looking in at cam but would onl need to T into a hose with a valve. JIm here had to make bigger oil pump to keep up with his protective rifle drilled cam so he knows the score on oil surfing.

Install Ludwigs trough, that will hold back pre-wear , without Ludie;s mod it's a chancers gamble.
The original oil diagrams show splash feed, as the cam rotates towards the crank the effect is to throw off oil from the crank, try splashing oil on to a cam spinning at 3000rpm in the lathe! A oil pressure wedge can only begin at the rear of the cam ..ie drawn in...the front facing the crank is thrown off!

Fast Eddie said:

comnoz said:

Actually the cam should never contact the edge of the lifter. The wear pattern tells the tale.

If you use early design lifters with the beveled edges and a race cam -the cam may contact the edge where the bevel starts. If it does they will not last long.

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I thought the wear pattern was caused by the 'edge'...?

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I was referring to the wear pattern on the lifter. You should not see the wear pattern go all the way to the edge of the lifter. Jim

These are the lifters out of my 750,to look at by eye they don't seem that bad.

Time Warp said:

These are the lifters out of my 750,to look at by eye they don't seem that bad.

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That looks like a normal but thoroughly worn out "wear pattern"

The is the type of lifter that will give problems with a big cam like a Norris D grind. The wear pattern then would go all the way to the start of the bevel and they would fail soon. Jim

try stellite tipped followers. Soft followers seem to wear cams quicker.

Norton followers are stellite tipped.

Time warp..those are time to replace! Glenn i am affraid you need new specks :lol:

john robert bould said:

Time warp..those are time to replace! Glenn i am affraid you need new specks :lol:

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Besides being worn they look smooth and shiny to the eye,the camera was unforgiving.
I seem to remember the cam 'looking OK with consistent lobe heights but picked up another out of a 72 750.
Good cam but worn out stellite faces. :?:
Why didn't Norton use a radius ed face ? (probably missing something obvious)

A package arrived from Jim recently containing another set (MikeVintageCycleParts) of lifters/followers that he had surface ground.

Radius follower changes the cam mapping, Velocette thuxtons changed the follower rad, opening is quicker...but the overall timining is the same.
I still say the lube is weak , trying to chuck oil drops onto a fast forward spinning cam is poor.

Time Warp said:

john robert bould said:

Time warp..those are time to replace! Glenn i am affraid you need new specks :lol:

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Besides being worn they look smooth and shiny to the eye,the camera was unforgiving.
I seem to remember the cam 'looking OK with consistent lobe heights but picked up another out of a 72 750.
Good cam but worn out stellite faces. :?:
Why didn't Norton use a radius ed face ? (probably missing something obvious)

A package arrived from Jim recently containing another set (MikeVintageCycleParts) of lifters/followers that he had surface ground.

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The 50s Triumph twins used three types of followers. The earliest ones were untipped and could wear hollow (concave). We welded up a set with cobalite and reground a convex radius on them - the bike went much slower. Even though the cams and followers were badly worn, the bike had been quite fast before the 'improvement'. Later followers were stellite tipped types with two radii available. The smaller radius items were used in Tiger 110 and Thunderbird. When the E3134 cam was used 'R' type followers were used which had a larger radius. In my racer I used flat followers with large base circle cams of stupid durations however not high lift. It used to rev t o 10,500 RPM. The different radii give noticeable effects on performance . I suggest they affect the lift rates, if you plot the lift verses the crank degrees you will see it if you do the comparison. One thing I always did was progressively change cam timings to find an optimum. I still do this with my 850 Norton. It might interest that I was recently in the workshop of our best private superbike racing person. He had the top off a Fireblade, and I noticed that the cams had been welded up. I asked him whether he set them for top end or midrange. He said he changed them to suit each race circuit.

TW
'These are the lifters out of my 750,to look at by eye they don't seem that bad.'

They don't seem that good to me. The dips must have an effect on the lift rates, both opening and closing. I'd have them reground flat.

john robert bould said:

Radius follower changes the cam mapping, Velocette thuxtons changed the follower rad, opening is quicker...but the overall timining is the same.
I still say the lube is weak , trying to chuck oil drops onto a fast forward spinning cam is poor.

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Disagree regarding cam lubrication. The crankcase is full of oil mist plus there is a continous supply draining down from the cylinder head and past the followers directly on to the cam lobes. Beneficial if the follower stellite faces are ground so as to retain oil as per cylinder surface after correct honing. I've had problems with unequal cam lobe wear on the original and replacement cam (circa 1988 - genuine Norton) but not since fitting chilled cast iron PW3 using 20w/50. Important to check PRV is opening at 55lb/sqin not before. This has an effect on the big-end and top end oil pressure and volume flow rate to these parts.

Oil mist and drips from the head! now thats a laugh :lol: when doe's all this happen :?: about 20 miles down the road :!: if all is well with the degign,,,why is there so many worn out in little miles :?: my Merc sprinter will do the clock round three times and still as no wear on the valve train...reason is on start up the cam gear is flushed with oil from oil jets from a huge supply...not some tear drop system that norton invented 60 years ago.

I met two Norton owners this year, both with over 100,000 miles on their 850 Commandos. One has had virtually nothing done, just a valve grind and a few bits, but needs overhaul now. The other had a top end rebuild at 70,000 and is going strong.

Glen

What ya bet those long lasting cam tales never bothered about wet sump draining. Norton must have as much or more oil thrown or dripped in liter lobe space than is being slung off or squeezed out. Oil jets and pre oiler would help but we'd need more oil pumping volume like comnoz drilling. The ZADP should protect on starts and shut downs, if ya don't let it idle long or wipes nano layer right off. Layer don't form till surfaces oil encounters is at least boiling hot.

As we have seen here. some cams are almost worn flat and the bike still runs OK :?: jims low mileage worn cams again show something is wrong. Come on the pump is just about Rubbish, it carnt be any good if the pressure drops to zero at ftat out revs.

worntorn said:

I met two Norton owners this year, both with over 100,000 miles on their 850 Commandos. One has had virtually nothing done, just a valve grind and a few bits, but needs overhaul now. The other had a top end rebuild at 70,000 and is going strong.

Glen

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