CAM & OIL PUMP GEAR HARDNESS

[autodeco57]

Any thoughts on this? '31 344 ci cam gear and meshing oil pump gear; the gear on the cam is integral with the cam, non-renewable. The oil pump gear is replaceable. The relative wear indicates that the pump drive gear is softer, sacrificial, to protect the cam gear. I have to get a pump gear made.

Question; what hardness should the pump gear be?

Is there tech information out there that addresses the issue?

The gear tech is recommending 4130 or 4350 material on the hardness scale if I remember the numbers right. He read a hardness of 3500 plus or minus on the old pump gear.

Steve Gorthy BCA #44510

1931 Model 87 five passenger

[AzBob]

Steve, I would heat treat the pump gear to a value similar to the old one. You would want it softer than the cam gear. Not familiar with the "3500" scale reading the gear tech quoted. 4130 alloy steel can be easily hardened up to 45+ on the Rockwell "C" scale and is a good choice for a gear.

[autodeco57]

Bob, thanks very much. This helps.

[Bob Engle]

4100 steel is chrome moly steel. 4300 steel is nickle, chrome moly steel. The last number 30 and 50 are the % of carbon in the steel. 30 is .3%. 50 is .5% carbon. the more carbon the harder the material can me hardened. The heat treatment process can control the hardness is the range for the max of the carbon content down to the annealed hardness. More carbon makes the material more brittle. The nickle makes the material flexible. Crome and moly make for toughness of the steel. I would opt for the the 4350 to keep wear low and control the hardness about 45 Rockwell.

Bob Engle

[autodeco57]

Thanks very much for the advice. The Rockwell number you quoted reminds me of what the gear machinist said; he was looking through a scope with a light at the old gear and pronounced it a "35", roughly. I thought that equated to the other index of numbers in the thousands range, but he actually said 35. The pump gear is about 3 times as worn as the cam gear. I went back and looked at the notes I wrote down and the specific numbers he gave me for the raw material were 4140 or 4340.

It sounds like you recommend the 4340...then treated to 45 Rockwell?

I take it that's a separate step after machining?

[Brian_Heil]

Could you get the hardness checked on say, the back side so the harness mark is not mistaken in the future for a timing mark? The unused unworn outer edge of the tooth would be available. Simple test.

On gear tooth hardening the case depth of the heat treated zone is ~0.020 deep max, more like 0.010 inch. The core material of the tooth is not hardened to keep it strong and not brittle.