While I was playing with the hardness tester

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comnoz

comnoz

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I pulled out a few cams.

The stock cam was from a 70 Norton. I don't know the mileage but it looked pretty nice.

The PW3 was from a racebike. Not my build. It was run for around 3/4 season and then the engine was torn down for a refresh. The cam looked good but the engine was modified with a quick change cam kit at that time.
The needle bearings ate right into the cam journals in about 15 minutes of run time.

The Combat cam was one I tested in my engine as a twingle.

 
Hi Jim,
You specified the PW3 cam as a "DNC PW3" if I heard correctly. What does the DNC mean?

Thanks,
Ed
 
Mr. Rick said:
Storm clouds gathering over Perth...
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Doubt it, an interesting article, but the same indenter used on all cams, cast iron usually needs a ball indenter or Brinell tester to achieve an accurate reading, nice to see what the steel cams measured though.
 
L.A.B. said:
David Newman Cams?

http://www.newman-cams.com/
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Been there, and asked a cam grinder inside the factory about cleaning up the lobes on the cam grinder when they came back from hardening/tempering-this is what he said when I asked him if he can keep them 100% accurate – “ we just turn the cam round on that one particular lobe until it cleans up”

Hench, you can get inaccurate cams for any bike/car! :oops:
 
Madnorton said:
Doubt it, an interesting article, but the same indenter used on all cams, cast iron usually needs a ball indenter or Brinell tester to achieve an accurate reading, nice to see what the steel cams measured though.
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Not with chilled cast. The chilled part is tested like hard steel.

Of course the bearing journal and base is too soft to get a useful reading with a Brale indenter. Jim
 
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A couple more things to note:

The wear resistance of a chilled iron cam and a hardened steel cam are not directly comparable by hardness numbers alone.

There were no corrections made for the curvature of the cam lobe so all readings will be slightly lower than actual -particularly those made at the top of the lobe.
 
Hi
Is there a 1:1 relationship between hardness and abrasive wear resistance?

Jim, when you state the base is too soft to get a useful reading, I take it you mean the base of lobes. I though lobes are hardened equally all way around? Which hardening process is employed for your tested camshafts? Whether cams are made of chilled chrome cast iron or nitrided EN40B steel, I'd expect surface hardness to be equal along the circumference.

-Knut
 
mdt-son said:
Hi

Jim, when you state the base is too soft to get a useful reading, I take it you mean the base of lobes. I though lobes are hardened equally all way around? Which hardening process is employed for your tested camshafts? Whether cams are made of chilled chrome cast iron or nitrided EN40B steel, I'd expect surface hardness to be equal along the circumference.

-Knut
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I am referring to the base of the lobes.

The two OEM cams I tested were case hardened steel. No nitriding.

The lobes of a quench hardened cam will always test harder than the base circle. During the quenching process the top of the lobe will cool faster than the base of the lobe - so it will be harder.

The DNC cam is chilled cast iron.
Only the lobes are cooled rapidly to make them hard. If the whole cam were quenched it would be too brittle to be of any use.

A weld up cam such as a Webcam or Megacycle is ground down to the base circle before the weld metal is added. The base circle becomes a little softer during the welding but the metal added during the weld is very hard. Generally the only heat treatment after weld-up is stress relief.

"Is there a 1:1 relationship between hardness and abrasive wear resistance?"

There is -only if -the metal is steel of the same alloy and it is run against the same followers.

The wear rate of chilled cast iron is very good. It gets harder with use.

That is part of the problem. Chilled cast iron has poor resistance to impact damage. And the harder it becomes with use, the more prone it becomes to failure from impact.

Impact results from valve train separation. Jim
 
Thank you Jim, very useful information.

I don't understand this though: Why would a camshaft made of chilled cast iron get harder with use? The carbides formed in the lobe during the casting process should be consistent to any sensible wear depth and if altered, then to a lesser amount of carbides, which would accelerate wear due to increased abrasion. This will in turn further soften the casting material. Cast iron will not work harden by pounding on the lobes.

-Knut
 
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mdt-son said:
Thank you Jim, very useful information.

I don't understand this though: Why would a camshaft made of chilled cast iron get harder with use? The carbids formed in the lobe during the casting process should be consistent to any sensible wear depth and if altered, then to a lesser amount of carbides, which would accelerate wear due to increased abrasion. This will in turn further soften the casting material. Cast iron will not work harden by pounding on the lobes.

-Knut
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I know that cast iron does not work harden as a rule but,

Any chilled iron cam I have hardness tested, tested harder with use where there was contact with the follower.
That has always led me to believe that chilled iron does harden with use. But I will admit, I am not well schooled when it comes to chilled cast iron.
 
Jim,

As the outer surface wears away, carbides will apear over over a broader area. This will probably contribute to your increased readings.

Deposits of stellite due to insufficient lubrication may be another cause.

-Knut
 
mdt-son said:
Jim,

As the outer surface wears away, carbides will apear over over a broader area. This will probably contribute to your increased readings.

Deposits of stellite due to insufficient lubrication may be another cause.

-Knut
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That does make sense.

I have also read that some types of chilled iron do have the capability of limited work hardening. Jim
 
I know you guys do not suffer fools gladly, and hesitate to ask, but if the followers are made with Delchrome C (is that right?), why are the cam lobes not using the same , or similar material?
 
The cam needs to be softer than the followers for longest wear.
Similar metals do not make for good wear properties in a sliding application.
 
comnoz said:
A couple more things to note:

The wear resistance of a chilled iron cam and a hardened steel cam are not directly comparable by hardness numbers alone.

There were no corrections made for the curvature of the cam lobe so all readings will be slightly lower than actual -particularly those made at the top of the lobe.
Click to expand...

Sometimes when cutting something which is very hard, it is better to use a softer grinding wheel than a hard one.
 
comnoz said:
I pulled out a few cams.

The stock cam was from a 70 Norton. I don't know the mileage but it looked pretty nice.

The PW3 was from a racebike. Not my build. It was run for around 3/4 season and then the engine was torn down for a refresh. The cam looked good but the engine was modified with a quick change cam kit at that time.
The needle bearings ate right into the cam journals in about 15 minutes of run time.

The Combat cam was one I tested in my engine as a twingle.

Click to expand...

So, we haven't really addressed the issue of the toasted needle bearings that Jim mentions. Insufficient lubrication? Or is the needle bearing concept just wrong, when bushings will carry more load with less lubrication? Was Paul Dunstall being too cute with the needle bearing recommendation?
 
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