We grind them offset to 2thou over std size
then balance them (& i`ll tell you why we balance them now in a min)
then we harden them (Nitriding)
then we grind them true (straight) both b/e & mains
& then balance them again. (generally this 2nd balance very little has to be done, if any at all.
the reason why we (my dad) has always done the strokers this way is because he was always
a firm believer in that if you grind it down offset, "close" to where you want the crank to end up at (size-wise) then most of the metal that has to come off the thing is done early in the process,,, then when it`s balanced obviously more metal comes off it
so then , in the hardening process, they grow & bend & do all sorts of wonderful things,,, so when you grind it true, (both mains & big ends), often that little bend from hardening gets ground out of it so the crank ends up straight & true with the last grind process...
this way the balancing that was done early & the first grind done before balancing, the crank needs only very little metal taken off it in the last balance process,,, this leavs as thick & as even "Crust" of hardening throughout the whole length/width of the crank.
if you can get what i mean?
most guys have a crank ground, hardened (if at all) & then just simply linished to final size on the journals,,, & then balanced (if at all)
so in this way the crank can be bent, & the hardening crust has been broken (usually) a little deep in places... it breaks that hardening crust.
my dad always said to do the extra processes --> do it his way
i`ve kept doing strokers this way since forever & so far we havn`t had any broken cranks
but i do know a few of dads old customers who have argued about the cost & didn`t want to do it "His-way" & funny enough their cranks broke,,, i could name & shame here but i won`t
anyways, just a story about dads mini crank metalurgy process
