Using Press to Remove and Replace Piston

[trbowgn]

I have to replace one of the pistons in the wagon (small crack on the ring gland) and was wondering how hard it is to press a pin out and put a new one in.
I have an Arbor press with all the blocks and fittings at work that we use for bearing all the time but wanted to know if there are any tricks or just press the pin out and press back in. Do they use any press fit locktight? Or am I better off just taking it to the shop and having them do it?

[turbovanman²]

I can't remember if 86 uses floating wrist pins or press fit. If floating, then you simply remove the clip and slide the pin out, if pressed, you can press it out, but then you should heat up the small end to avoid damaging the rod and piston or heat it up to remove as well but DON'T overheat it otherwise you'll damage and weaken it.

A machine shop will probably charge $15-$20 to swap over a pressed pin piston, personally, that's worth it.

[Directconnection]

'86 will be a pressed pin and I won't suggest you trying it as you will need a special fixture. otherwise all you'll do is crack the piston and chunks will fly off everywhere except the part you need to come off. The OD of the piston is round... and you don't press on that. Your fixture has 2 legs for some, or a round cylinder with 2 flats to clear the side boss of the piston. To put it on, you need to make sure there's sufficient press fit (.0020 to no less than .0007) and if re-using the old pin, you'll need to spin it in a lathe or mandrel and scuff it up with scotchbrite really good to get any/all burrs off it that were put on when pressing the old pin out. If you install it.... use heat until the small end is entirely blue (not cherry!) And with the piston's small end all lubed up, QUICKLY slide the pin in and center it. You'll have only 1-2 seconds to do this or it jams up... and pressing the piston WILL ruin it, unless you have lots of experience with them and correct fixtures. When I installed them at work, we had a stop in the side of the vise that was adjustable and had to legs the made contact with the recessed part of the piston at the pin boss. (piston hits/stops there... pin hits adjustable middle part of stop) If lets say your rod's small end is .900" wide.... and the inside of the piston bosses are 1.050" wide, then that means you'll have .075" gap side to side. Now.......put the pin in the piston just for the set-up part of this discussion. Center it....if the pin sticks out of the piston .050" then add that .075" to it. So, when you set your stop, and put the piston up to it, the pin should be hitting the inside adjustable stop and be sticking out of the piston .125" When you heat up the rod, place the piston against the stop nice and square with the pin lubed and installed (but obviously offset so the rod will fit into the piston) Take the rod out of the hotbox/whatever you heated it with.... and insert into the piston. Now the uber-tricky part: have someone push in the pin while you slightly give the rod a wiggle or two AND pushing it seated up against the side of the boss (offseting it) and wait a few seconds..... Having the rod all the way to one side of the piston, and that pin stop set so the pin is offset .075 now mean that when you center the rod in the middle of the piston via eyeball... the .075" is gone and the rod/pin are perfectly centered.

If you have a junk identical rod laying around, you could bore out the small end, and put a setscrew in it and use that as your setup so you don't have to do the math....

[turbovanman²]

Bored today Steve? :eyebrows:

[trbowgn]

'86 will be a pressed pin and I won't suggest you trying it as you will need a special fixture. otherwise all you'll do is crack the piston and chunks will fly off everywhere except the part you need to come off. The OD of the piston is round... and you don't press on that. Your fixture has 2 legs for some, or a round cylinder with 2 flats to clear the side boss of the piston. To put it on, you need to make sure there's sufficient press fit (.0020 to no less than .0007) and if re-using the old pin, you'll need to spin it in a lathe or mandrel and scuff it up with scotchbrite really good to get any/all burrs off it that were put on when pressing the old pin out. If you install it.... use heat until the small end is entirely blue (not cherry!) And with the piston's small end all lubed up, QUICKLY slide the pin in and center it. You'll have only 1-2 seconds to do this or it jams up... and pressing the piston WILL ruin it, unless you have lots of experience with them and correct fixtures. When I installed them at work, we had a stop in the side of the vise that was adjustable and had to legs the made contact with the recessed part of the piston at the pin boss. (piston hits/stops there... pin hits adjustable middle part of stop) If lets say your rod's small end is .900" wide.... and the inside of the piston bosses are 1.050" wide, then that means you'll have .075" gap side to side. Now.......put the pin in the piston just for the set-up part of this discussion. Center it....if the pin sticks out of the piston .050" then add that .075" to it. So, when you set your stop, and put the piston up to it, the pin should be hitting the inside adjustable stop and be sticking out of the piston .125" When you heat up the rod, place the piston against the stop nice and square with the pin lubed and installed (but obviously offset so the rod will fit into the piston) Take the rod out of the hotbox/whatever you heated it with.... and insert into the piston. Now the uber-tricky part: have someone push in the pin while you slightly give the rod a wiggle or two AND pushing it seated up against the side of the boss (offseting it) and wait a few seconds..... Having the rod all the way to one side of the piston, and that pin stop set so the pin is offset .075 now mean that when you center the rod in the middle of the piston via eyeball... the .075" is gone and the rod/pin are perfectly centered.

If you have a junk identical rod laying around, you could bore out the small end, and put a setscrew in it and use that as your setup so you don't have to do the math....

I'm to lazy to read all that. Machine shop here I come

[Directconnection]

Bored today Steve? :eyebrows:

Nah, just got horned up over technical blabber stuff that I used to do at work.



I'm to lazy to read all that. Machine shop here I come

Good choice! {on the machine shop part... bad choice on the other}

[trbowgn]

Thanks Steve, it was actually a very informative reply