Would cooling the wrist pins down liquid nitrogen and heating the rods up to around 600 degrees F get me enough clearance to install the pins easily into the rods? I have access to both liquid nitrogen and dry ice (used with acetone to pre-cool the pins) for free, so if it works, it would be one less thing I have to pay for to do my engine rebuild. That, and there would be no need to heat the rods up a lot.

 

I have tried it just for kicks with a wrist pin out of the freezer, and a rod out of a 450° oven, and it slid in, but only took a few seconds before it wouldn't move again. I would think you could do it, just have an accurate method or homemade jig for setting its side to side location.

 

Im going to make a jig to hold the rod and piston so I can hopefully drop the pin in. Liquid nitrogen gets down to like -300 degrees F. or something so it'll be about as cold as it gets so I should have a little time to maneuver it. Question is how much liquid nitrogen will it take to cool 8 pins by 200 degrees.

 

I can't know how much nitrogen. Does freezing something that far affect its properties (like the reverse of heat treating)?

 

I know steels structure does change at exremely cold temps. Come to think of it, the press fit is only like .002", so the nitrogen may be way overkill. Heating the rod in an oven and cooling the pin in dry ice/acetone may be enough to allow me to drop the pin in. Ill have to get a junk rod and pin and try it out.

 

If it was that easy I'm sure the engine rebuild shops would be doing it. Heating up the rod end with a special multi burner torch and dropping in a pin from the freezer is the accepted way to do it.

I think if you supercool the pins, you'll make them very weak and brittle.

Pay your machine shop to do it right or buy some floating pin pistons and rods.

 

How hot do they get the rod end? 500-600 degrees? Also, doesnt this allow for enough clearance for the pin to be inserted with little force?

 

The steel properties would only be affected while cold. When they warm back up, they'd be the same.

There are a lot of outfits doing cryo treating of parts these days. Brake rotors, for instance. Improves their fatigue resistance IIRC. But, those parts are designed from the beginning for the cryo treating (alloy choice, cold working, heat treatment, etc.), so while I don't think it would hurt the pins to dunk them in LN2, I would also say if it was a good idea, you would have already heard about it.

 

Also, doesnt it take some time for the transformation to the steels structure to take place?

My biggest question is whether it would give enough clearance, and enough time to assemble the parts before the pin and rod lock together.

 

Vizard mentions doing this in one of his books. Just mentions your normal oven and your deep freeze.
Just slide it in quickly with your thumb. IIRC it isn't a bearing clearance, you just need it to be ~3/16" from poking out the far end or something. Not a lot of precision is needed.

However if you get it part way in and it hits a burr, or just plain gets tight, you're screwed and have to go to a machine shop then. But hey, nothing ventured nothing gained right?
Just make sure you oil the pin so it'll slide in nicely.

 

You can call me old fashioned if you like but I perfer to use the hand powered hydraulic press with the parts at room temp. If you heat/cool the parts and slip fit them together, you wouldn't be able to tell if the rod end was "loose/oversize". With a press you can "feel" if one goes in too easy.
Just my .