Piston Wrist Pin

[raspii]

Hi Guys,

Something that has caught my eye while viewing some of the amazing work on this site is the piston wrist pin and if any special treatment is conducted to it during the construction stage.

Currently i have made mine from silver steel and sanded to a fine finish using emery paper. Does anyone harden theirs also by heating to a dull red and then quenching in water?

I saw it somewhere and thought i had better check, i have reamed the aluminium pistons so they are all nice and smooth, but just checking if the wrist pin would be strong enough, of if you need to give it a little bit of a harden too?

Any help as always is greatly appreciated,

From Pat

 

[Cogsy]

Hardening won't give it any more strength, and will make it more brittle and therefore less suitable for shock loading. The only time it would need to be hardened would be if you were running needle roller bearings on it, and even then case hardening would be the way to go. There is plenty of strength in the drill rod and it will be fine as a wrist pin.

 

[raspii]

Thanks Al,

Greatly appreciated,

Will keep on makin the swarf

 

[abby]

I would doubt that anyone attempts to harden silver steel by quenching in water from dull red ! Silver steel should be heated to CHERRY red ie. about 780°C , the temperature should be maintained for an hour per inch of section before quenching in clean cold water.
The hardened parts will now need tempering to a hardness level or toughness commensurate with the application.
The most common method of tempering is by observing the oxide colour change during careful re-heating of the polished part , from pale yellow(hard) through to dark blue(springy) , and again quenching in water at the desired colour.
The use of a domestic oven and accurate temperature measurement is probably the best way to ensure correctly tempered parts especially for very small items and springs.

 

[Mechanicboy]

I had never hardened the wrist pin made of silver steel, better to retain toughness instead hard and brittle wrist pin. Keep all surface well polished against abration.