Piston ring compressor tool for air compressor rebuild?

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Bill Crowell

Bill Crowell

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On a reciprocating air compressor, since you can't install the pistons from the top of the cylinders because the connecting rod bolts face upward (i.e., you have to install the rod bolts, pistons and rings first and then lower the cylinders over the pistons) and therefore can't use a normal ring compressor, are you supposed to use the kind of ring compressor that they use on chainsaws?

Just wondering if I need to order one. I tried researching it but came up with nothing, and wonder if any of my FABO brethren have had this problem.

ring compressor.jpg
 
I'm not sure what compressor you may have but on Quincy compressors (and many others I have worked on) the bottom of the cylinder has a 45 degree taper. No ring compressor is necessary if you have that design. You simply invert the cylinder so the bottom is up and take the piston with the connecting rod and position it in the taper. Be sure to oil it well and you simply use you fingers to assist the rings in compressing as you gently wiggle and push the piston in.
This was only necessary on cylinders where the connecting rod bearing was wider than the diameter of the cylinder (usually the high pressure piston). If the rod bearing is smaller than the cylinder diameter (low pressure typically) then it could be installed from the top using an automotive ring compressor, but if the cylinder was removed, then it is probably easier to just use the taper on the bottom of the cylinder bore.
I hope this helps, I realize not all compressors are built the same. I used to train our mechanics at the nuclear plants we operated in overhauling our compressors and most of them were this way.
Be sure to look at the rings as some will have a top side which is usually denoted with a small dimple or "pip" as Quincy calls it. If you are not sure which way they go (if the rings are not of a symetrical cross section) look up a service manual for your compressor.
Hope this helps.

Reference only...check YOUR manual, but this is what I'm talking about with the rings
upload_2022-9-5_6-13-14.png

This is the only pic I could find on the internet showing the piston installation...not very good I know. If you look carefully at the larger low pressure piston to cylinder area you will notice the dark band...that is the taper that assist in the ring compression.
upload_2022-9-5_6-31-17.png
 
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Wow, ACME SS, great answer! Thanks for all the effort. I was able to lower the cylinders over the piston rings by carefully pushing the rings into their lands with a tiny screwdriver, but was just wondering how to do it next time. Thanks again!
 
Hose clamp. Just like we used to do on dirt bike engines. Or a vw piston ring compressor, just have to modify the band.
 
My DeVibiss/Craftsman had a leather compression ring.
 
Bill Crowell said:
Wow, ACME SS, great answer! Thanks for all the effort. I was able to lower the cylinders over the piston rings by carefully pushing the rings into their lands with a tiny screwdriver, but was just wondering how to do it next time. Thanks again!
Click to expand...
Yep it can be done like you did but it is pretty tricky. It's easier when the rods are not bolted to the crankshaft. Good job.
 
Tooljunkie said:
Hose clamp. Just like we used to do on dirt bike engines. Or a vw piston ring compressor, just have to modify the band.
Click to expand...

Good point, Tooljunkie. I didn't happen to have the right size hose clamp at the time. I'd better pick one up the next time I go to the auto parts store.
 
I have opportunity to by a nice looking Belaire that supposed to have bad head from dealership. They didn't have time to have it repaired and bought a new one.
 
I used to work at a small engine shop. I always used zip ties for dropping the chainsaw jugs on. Did it on my motocross bikes too.
 
Bill Crowell said:
Good point, Tooljunkie. I didn't happen to have the right size hose clamp at the time. I'd better pick one up the next time I go to the auto parts store.
Click to expand...
If you are inserting the piston into the bottom of the cylinder where the taper is, the hose clamp will not work, only if you are putting it in the top. Some compressor piston rod to crankshaft bearings are wider than the diameter of the bore so you have to go in from the bottom on those and you simply work them with your fingers or maybe a wooden popsicle stick.
 
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