Edbro LNC Hoist Repair - Replacing Piston Cup Seals

[Blueacre]

I purchased new piston cups for the hoist on my farm truck. It is an Edbro LNC - the ones with the tank and valve on the bottom of the hoist cylinder. It is a 3 stage cylinder.
I got the hoist apart with no problem and ready to install the new cup seals - they flare out quite a bit to the seal lip and are a very hard fabric reinforced rubber. I am not 100% sure how to install them and get them past the internal threaded end of the cylinder without damaging the seal lip. I am thinking I could wrap a piece of 3 inch wide brass shim stock I have around the seal area and start that into the cylinder till it is past the threaded area and then push the piston through the shim stock and into the cylinder.

Appreciate if anyone with experience rebuilding one of these hoists has any suggestions - Would it help to heat up the seal with a heat gun before pushing into the cylinder ?

Typical pictures of this style hoist and the cup seals attached.

 

[Vetech63]

You can squeeze those down with a large hose clamp or use a ring compressor.

 

[Blueacre]

My ring compressor has a rib on it and wouldn't let it go in far enough to clear the threads. I ended up wrapping a piece of brass shim stock around the cup seal and tightening a gear clamp around it to compress everything. Was able to push the piston in a little ways - loosen the clamp and move it back 1/2" then tighten and push piston in a little more - repeat till shim stock was in to the end of the threads and then push the piston in without the shim stock moving so the seal was into the bore and then pulled the shim stock out. Took a little trial and error the fist one - if I pushed the piston in too far past the threaded end the shim stock wedged between the seal and the cylinder bore and couldn't get it out.