soft cam

comnoz · Apr 10, 2011

I have a nice hardness tester and over the years I have tested a lot of Norton cams. Both the ones that were supposedly good and the ones that were supposedly soft like the MK3 cams. Both good cams and failed cams.
Generally I have seen hardness range from about 50 to 65 and had pretty much decided that the soft cam deal was just a wives tale.
However today I pulled an old Mk3 motor apart that had a hole in the cases and had been laying around for years. The cam was showing some wear but probably usable. I put it in the tester and wow. 35RC. Just to see if I was doing something wrong I pulled out a pile of cams and saw the normal 50 - 65 on the lobe but I must say- I found a soft one. Jim

Hobot · Apr 10, 2011

Ugh, not what Norton He Men want to find, thank goodness its not mine.

cjandme · Apr 10, 2011

That's probably what happened to my motor. The PO said that one of the lobes had come apart & that he thought that his PO had put in a "hot cam" with a welded on diffrent profile (he had bought it as a basket case). That was twenty odd years ago, so it was probably a cam from the "soft batch". I think it's in with the box of parts that came with the bike, I could take a look and send it to you if you like. Cj

comnoz · Apr 10, 2011

cjandme said:
That's probably what happened to my motor. The PO said that one of the lobes had come apart & that he thought that his PO had put in a "hot cam" with a welded on diffrent profile (he had bought it as a basket case). That was twenty odd years ago, so it was probably a cam from the "soft batch". I think it's in with the box of parts that came with the bike, I could take a look and send it to you if you like. Cj

Welded up cams usually work very well. The hard weld overlay is a good wear surface if done correctly. The cam you have would likely make a good core to send for a weld and a regrind if the bearing journals are not damaged. I would be glad to test it if you want the results. Jim

cjandme · Apr 10, 2011

I've been out in the garage looking and had just about given up when I found it, so...yes It would be great to find out about it. Cj

GRM 450 · Apr 10, 2011

Hello Jim,
Did the soft Mk3 cam have a "P" stamped in the end?
Mine did and I tried to find out what the "P" meant. I think it was Nick from Andover??? said it meant Parkerised? (don't quote me on Andover as I asked questions every where and this was the only answer I recieved)
I looked up Parkerised and it is a coating put on guns etc to stop rusting and look nice.
Can't see why anyone would be concerned about a cam rusting or looking nice when it lives in the oily black innards of an engine.
It was very soft also.

Graeme

RennieK · Apr 10, 2011

I had a ss cam in a 1972 750 combat that I bought brand new that had 2 lobes that seemed really soft. One was worn down about .300 (by memory) after not too many miles. It was so long ago but I'd guess I had somewhere around 5000 miles on it max. I was using the recommended 20/50 oil back then.

comnoz · Apr 11, 2011

GRM 450 said:
Hello Jim,
Did the soft Mk3 cam have a "P" stamped in the end?
Mine did and I tried to find out what the "P" meant. I think it was Nick from Andover??? said it meant Parkerised? (don't quote me on Andover as I asked questions every where and this was the only answer I recieved)
I looked up Parkerised and it is a coating put on guns etc to stop rusting and look nice.
Can't see why anyone would be concerned about a cam rusting or looking nice when it lives in the oily black innards of an engine.
It was very soft also.

Graeme

Yes it is stamped P. and still has that black coated look. Parkerizing leaves a very thin hard coating but doesn't last very long. Jim

comnoz · Apr 11, 2011

RennieK said:
I had a ss cam in a 1972 750 combat that I bought brand new that had 2 lobes that seemed really soft. One was worn down about .300 (by memory) after not too many miles. It was so long ago but I'd guess I had somewhere around 5000 miles on it max. I was using the recommended 20/50 oil back then.

I have 6 of the SS cams here, some scrolled and some not and a couple with wiped lobes but they all test over 60RC. I think a lot of the cam problems back then were caused by the multi viscosity oils that were available at that time. Poor base stock and the addition of lots of VI modifiers made an oil that broke down quickly in a Commando motor.
I have a new factory cam here for a small block Chevy and it only tests 40RC. Jim

comnoz · Apr 11, 2011

cjandme said:
I've been out in the garage looking and had just about given up when I found it, so...yes It would be great to find out about it. Cj

You can send it to : Jim Comstock, 1277 21st Lane, Pueblo Co. 81006 and I will test it. I commonly pay 15 bucks for a cam core so if you want to sell it or trade for something you need let me know. Jim

prmurat · Apr 11, 2011

Not soft?

Here is my MK2 cam after 12000 miles...both exhaust lobes looked like this:

Philippe

comnoz · Apr 11, 2011

I wouldn't say your cam was not soft.
Here is the cam that holds the record for the softest I have measured. [in front] It measures 35RC. The speedo says 13,500 miles. The bike ran out of oil and stuck a rod through the case.

And here is a SS cam from a bike with under 10,000 miles. It measures 62RC

This isn't the only time I have seen this and it gives me the impression that the cams hardness was not the root of the problem. More likely lubricant failure. Jim

swooshdave · Apr 11, 2011

Why exhaust side only?

comnoz · Apr 11, 2011

swooshdave said:
Why exhaust side only?

Good question. Maybe the outer two lobes get more oil from the hole in the con rod.
But on the soft MK3 cam the two inner lobes are perfect and the two outer lobes show some wear. Jim

Cheesy · Apr 11, 2011

Where are you taking the measurements from? Im guessing that a Rockwell test on a radiused surface will give a slightly lower reading. It seems odd that one of the hard ones is that worn. Is it possible that they were just case hardened, or not case hardened deep enough ie not below the maximum hertzian contact stress depth?

comnoz · Apr 11, 2011

Cheesy said:
Where are you taking the measurements from? Im guessing that a Rockwell test on a radiused surface will give a slightly lower reading. It seems odd that one of the hard ones is that worn. Is it possible that they were just case hardened, or not case hardened deep enough ie not below the maximum hertzian contact stress depth?

I am taking the measurement about halfway up the side of the lobe. I have an offset roller fixture made for cams. The older cams are definitely case hardened and I have found the hardening to be quite deep on any I have cut into. Jim

swooshdave · Apr 11, 2011

comnoz said:
swooshdave said:

Why exhaust side only?

Click to expand...

Good question. Maybe the outer two lobes get more oil from the hole in the con rod.
But on the soft MK3 cam the two inner lobes are perfect and the two outer lobes show some wear. Jim

Maybe this is daft what about measuring the springs? Could excessive spring force be a contributing factor?

Cheesy · Apr 11, 2011

swooshdave said:
comnoz said:

swooshdave said:

Why exhaust side only?

Click to expand...

Good question. Maybe the outer two lobes get more oil from the hole in the con rod.
But on the soft MK3 cam the two inner lobes are perfect and the two outer lobes show some wear. Jim

Click to expand...

Maybe this is daft what about measuring the springs? Could excessive spring force be a contributing factor?

It may also be feasible that the deflection in the cam (bending between the two bushes) causes uneven loading across the face of the cam lobes, this will be worse on the exhaust lobes than the inlet lobes. I think that the bigger picture may have more to do with oil and engine speed though, over and above the load from the valve springs will be the loads from accelerating the valve gear, this is proportional to the mass/inertia multiplied by the acceleration, which with a cam is proportional to the speed. So basically as the engine goes faster the contact stress on the cam will go up massively and if the oil isnt there (or not enough) it will die a quick death

comnoz · Apr 11, 2011

I pulled my box of failed cams out and took a count. I have 14. They seem to be pretty evenly split between exhaust lobe and intake lobe failures.

I am going to go back to my original idea that the poor quality multi vis oils that were available in the 70's was the main problem with Norton cams.

By the way the new PW3 cams only measure mid 40s for hardness also. About the same as the average MK3 cam. Obviously they don't need to be very hard as longs as there is lubrication. Jim

Cheesy · Apr 11, 2011

comnoz said:
I pulled my box of failed cams out and took a count. I have 14. They seem to be pretty evenly split between exhaust lobe and intake lobe failures.

I am going to go back to my original idea that the poor quality multi vis oils that were available in the 70's was the main problem with Norton cams.

By the way the new PW3 cams only measure mid 40s for hardness also. About the same as the average MK3 cam. Obviously they don't need to be very hard as longs as there is lubrication. Jim

Would I be right in saying that the PW3 cams are a different material (chilled cast iron) to the standard cams? I hope they are good enough as thats what Ive got for my one.... It is true though that good oil can hide a magnitude of sins

soft cam

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