RS-550 and AndyMark am-0928 pinion

[Tristan Lall]

Originally Posted by WileyB-J

Get the pinion red hot, then quickly press it on and let it air cool. Heat+metal=expansion

That also equals heat treatment, and probably not the good kind.

If the pinion is steel, if you get it red hot and then cool it slowly, you risk either annealing or normalizing it (from the heat), and inducing a soft microstructure (from the slow cooling). Cooling it faster will tend to harden (and thus strengthen) it, but the proper rate to achieve particular properties depends on the alloy composition. (Check the ASM Handbooks.) It's most definitely possible to harden it too much if you quench it rapidly. You'll also form an undesirable oxide layer on the surface, unless you've made preparations to carburize or nitride the steel instead. (Hardened steel gears are often finished by grinding to remove the oxide; carburizing and nitriding are not worth the trouble here.)

If the pinion is brass or bronze, you'll probably soften it by getting it red hot. For those materials, you can't restore the hardness and strength as above.

You might get better results by putting it in a household oven at its maximum temperature, which probably won't be high enough to ruin a steel pinion, but which will induce some thermal expansion.

If it were me, though, I think I'd just find an undersized and a nominal reamer, then get an arbour press and install it more carefully that way.