Wrist Pin Tips?

adsm08 · Jun 22, 2018

So this is something new to me in terms of engine building. I am helping a friend with rebuilding a Pontiac 400. We got the block back from the machine shop, and it is not .030 over, so new pistons. We have a weight matched set, as verified by my shop scale, so balance shouldn't be too much of an issue.

The problem we are running into is getting the new pistons on the rods. They are press-fit pins. I have a press, but neither of us has ever replaced pistons before, and I am finding a lack of instructional videos that don't involve cooking the rod. I took an old piston off the rod and tried to put it back on tonight, and cracked it. That was quitting time.

After we cracked the old piston I did take a crappy socket that the pins fit in and cut it down a bit on one edge so it can fit between the piston's bottom land and the pin (if it starts coming out the other side) but before I go any farther than that tonight.

So does anyone have any tips for setting the new pins in without breaking stuff?

swynx · Jun 22, 2018

Heat up one and freeze the other. You get about 3 seconds to push them together. There's videos on YouTube of this. But idk that I recommend this method.

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adsm08 · Jun 22, 2018

swynx said:
Heat up one and freeze the other. You get about 3 seconds to push them together. There's videos on YouTube of this. But idk that I recommend this method.

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Which is why I specifically asked for ideas that do not involve heating the rod.

swynx · Jun 22, 2018

My bad, I just skimmed your post really quick and missed that. All the methods of heat I've seen involve a torch until it's blue hot. I would be opposed to heat with the oven, and the pin in the freezer and trying to press that. That's how we do a lot of gear sets. So I wouldn't think that would mess up the piston.

My friends and I always have them pressed while being balanced. But we always wondered how they press them at the shop. Because we've tried without heat before and just break them.

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ElectraRider · Jun 22, 2018

used dry ice removing and installing piston sleeves in a truck one time.

Ewgoetz · Jun 22, 2018

ElectraRider said:
used dry ice removing and installing piston sleeves in a truck one time.

This is probably the best method.
I did that once changing out bushings in a loader to bucket attachment. Tried heating the loader part but had a hard time.
Put the bushing into dry ice and it slid right in real fast.

alwaysFlOoReD · Jun 22, 2018

Many moons ago in a faraway land in an old building I saw the magic they used to get pins into rods. It was a hot plate with a cake pan filled with sand and a small fridge beside it.

adsm08 · Jun 22, 2018

Yeah, the thing that pisses me off about this is that we were supposed to get an assembled short block back from the machine shop, but my idiot partner on this project didn't take the connecting rods to them with the rest of the engine, and ignored multiple calls from them to bring the rods down.

Dirtman · Jun 22, 2018

We always keep press fit parts like pins and bushings in a commercial deep freezer set to -20. This is usually plenty without using any heat on the other parts. Im not a fan of heating ethier since the drastic temp change from frozen to burning when pressing in the part can cause stress fractures.

adsm08 · Jun 22, 2018

Dirtman said:
We always keep press fit parts like pins and bushings in a commercial deep freezer set to -20. This is usually plenty without using any heat on the other parts. Im not a fan of heating ethier since the drastic temp change from frozen to burning when pressing in the part can cause stress fractures.

I do have a freezer that can do -20.

alwaysFlOoReD · Jun 22, 2018

I'm not used to thinking in Fahrenheit. -20 to 72 is = 124 degrees difference. Boiling water minus room temp is 140 degrees. Add a fridge and the variance is ~ 172 degrees. That seems to be pretty small to cause stress fractures in something that sees over 212 in work and who knows how much stress from switching directions twice every rev [up to] 5500 rpm.

PS; I forgot to add in my first post that the sand was heated to about boiling water temp.

Wrist Pin Tips?

adsm08

Senior Master Grease Monkey

swynx

Active Member

adsm08

Senior Master Grease Monkey

swynx

Active Member

ElectraRider

Active Member

Ewgoetz

Member

alwaysFlOoReD

Forum Staff Member

adsm08

Senior Master Grease Monkey

Dirtman

Former Middleweight Moss Fighting Champion

adsm08

Senior Master Grease Monkey

alwaysFlOoReD

Forum Staff Member

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