Paul Gray's Tips on Babbitt
|Some Babbitt tips:
1- Buy only what is termed #1 alloy, this ~92% tin, 4% copper and 4%
antimony. This has the best fatigue life and hot strength of the alloys I've
surveyed from ASM books. The Antimony keeps the alloy from shrinking when it
freezes. The lead stuff is lots softer and costs just as much as the good
stuff so.......Boy the lead causes the tensile strength to drop off like mad
2- Pour this alloy at 800-840°F. I am lucky enough to have thermocouple
probe and readout for this. Alloy will just turn yellow/ tinge of purple on
surface after skimming. Some use smoldering splinter to ascertain this.
3- Keep the pot clean and skim only when you have to. The more you skim the
more tin you remove from the alloy. Makes the bearing harder if you melt
small quantities of alloy. Keep the ladle in the pot to ensure minimum heat
loss to poured bearing.
4- Be sure to have anchor holes in bearing shell or tin the shell using
stuff available commercially. Bearing has to bind to something. In Craigs
case, a strip on a cross head.
5- I pour model T bearings and have to preheat because the shells are thin
and the sprue holes narrow. I think preheating is a good idea from a safety
point as you are SURE all is dry if it spit sizzles. I had a moist mold
which flung alloy 20' across garage where it splatted on wall....wear heavy
cotton, cover neck wear glasses minimum or face shield.
6- If you preheat, you'll notice the surface lots shiner and less ripple...
this is good. I use an oven set to 400F for preheating caps and molds. If
you use dimples to anchor bearing and you screw up, you just pry out shell
and try again. If you tin the bearing and screw up, you have to melt out old
bearing and try again. My first attempts at a T block took ~12 tries till I
figured out the correct preheat. I ended up parking the block in front of
kero torpedo heater till I got it to ~300°F.
7- you'll like the way the #1 alloy carves and finishes. Machines nice too
!! After I figured out how to do it, the guy who lent me the original model
T molds had me do one for him. I did this one in about 1 hour, bang, bang,
bang three saddles and caps. After I line bored it, the guy picked it up
and his buddies worked like mad to get it in a car for a tour. He ended up
driving it 200 miles up in PA hills without a hitch (whew).
The Model T Ford service manual has an excellent chapter on pouring and
finishing bearing shells.....You know, the black bible.