The Stovebolt Site Forums The Shop Area General Truck Talk pressing piston pins

hi getting ready to press the pins back on my rods with new pistons they were real hard to press out can i heat the rods in hot oil or should i just press the pins back in the rods with them well oiled dont want to brake the new pistons and i cant seem to find any inf. on pressing rod pins on gm rods thanks for help

Freeze the pins? Works with other things I've worked on.

You can also raise the temp of the small rod ends and pistons in hot water(safer then hot oil). Just make sure you dry them completely after assembly.

Hot water won't cut it.
http://www.sunnen.com/product_detail.jsp?id=29&prod=CRH-60+Rod+Heater&catId=63&lnk=

Have a shop do it.

I don’t have any idea what your background is Fire, or what you’re working on, or what your shop capabilities are so it’s a little difficult to answer your question.
Let’s start out this way, if you try to assemble parts by thermal expansion i.e., freezing one heating t’other you better be real quick because as soon as they touch each other the temperatures begin to equalize and you only have a few seconds to get it right. That works pretty good when your trying to assemble a steel bearing into a magnesium or aluminum housing where all you have to do is drop it in and when it hits bottom, your home. An example of this would be axle bearings into the magnesium side covers of a Halibrand quick-change rear end. You also have the fact that these are two materials with very different coefficients of expansion, unlike steel to steel.
Next if you have a hydraulic press the job is easy and it is the way it would be done in a proper engine shop.
The pin slips freely or floats through the first side of the piston and can be press into the rod to make full engagement, just till it is flush with the bottom side of the rod. I would use a solid spacer, probably aluminum, between the rod and the boss on the second side of the piston just so you don’t nick the piston. I would also press against a soft material like aluminum, to support the piston on the press table to keep from nicking up the outside of the piston. All you are doing here is compressing the second side boss of the piston, which should not hurt anything. Next I would place a spacer under the rod to take up the side play. A slotted clearance hole in the spacer will allow you to press the pin in a little further through the rod, far enough to give you a pilot into the second piston boss. Remember that you have to pull the spacer out so it has to be U shaped, slotted spacer and again don’t nick the piston. At this point you can drop the exposed portion of the pin into the second side of the piston and press it home until it is even on both sides. I would turn up a stepped plug (similar to a Champaign cork) that would drop into the pin to press against. I made this one in the upper picture to press sleeves into wheel cylinders: http://rides.webshots.com/photo/2623085370098611668ETUIML
This all sound like lot but once you have all the pieces together the actual job only takes a few minutes.
If you’re not equipped to do this or don’t feel comfortable with it, any auto machine shop will press them in for a minimal amount and it should only takes a few minuets.
Hope this gives you some ideas.
Denny Graham
Sandwich, IL

Having pressed a few thousand rod/piston combinations in 45 years of auto mechanic and machine shop work, I've developed some pretty definite opinions on the process. Pressing works well, and, in fact, is the only way to disassemble a piston and rod combination. Each piston and rod setup takes specially-formed fixtures to support the piston properly, plus a dedicated pin pusher for each assembly. Reassembly is another matter, and most top quality shops use a heater to expand the small end of the rod, and use a preset fixture to slide the wrist pin into the hot rod. It's a one-time chance to get it right, as there's usually less than 5 seconds available to get the wrist pin inserted to the proper location before the temperature equalizes and the rod grabs onto the pin.

Pressing the pin into the rod puts major stress on the pin boss on the lower side of the piston, and usually creates tight spots that interfere with proper wrist pin lubrication. Since the average pin-to-piston clearance is only 4/10,000 inch, there's no room for error. I like the burner-type heaters rather than the electric ones, because a natural gas or Propane burner is much faster to operate. I can assemble 8 rods with the burner in the time it takes to do 3 or 4 with an electric rod heater.
Jerry

I would take them over to a shop and have them done. charge would not be that much and it would be done right. Take the word of Hotrod Lincoln he has the knowledge to do it right the first time.

Heating the rod end is the way to do it. I have watched a buddy of mine assemble many pins this way. The small end goes in a bench top furnice. The pin is put in one side of the piston. He pushes the pin through by hand and centers the pin by feel. Of course I am sure he has assembled thousands of pistons this way. Take them to a good shop to assemble.

I have an example of the damage you can do trying to press a piston on a rod with a shop press. A customer brought a piston and rod he had tried to install to the shop where I work. He had mannaged to gall the pin in the rod and it cocked slightly when it went into the piston on the other side, this pushed an wad of alumium up on one side of the pin bore. He wanted us to finish putting it on. He ended up having to get a new piston and rod because of the damage. Let an automotive machine shop do it you'll be better off in the long run.

Sean

ill see if there is a shop in my area that can do it i sure dont want to brake the new pistons its for a geo metro floats in the piston tite in the rod they pressed out ok but very hard i just have a little 10 ton press thanks for advise