Piston ring expander and compressor

[Gordon]

What do use for installing rings on a piston and how do you install the piston with rings in the engine? I have not found any good ring expander or compressor similar to what is used for an automotive engine. I have tried to make an expander and just tried to ease the ring over the edge of the piston but I frequently end up distorting the ring. For a compressor I have tried using a rolled up piece of shim stock with a hose clamp around it but it is hard to get it round with the small diameter of the pistons.

Any ideas?

 

[mayhugh1]

I usually turn a shallow taper on the bottom of the cylinder bore or the liner bore if I'll be able to insert the ring'd pistons from that end. With some oil, the taper will safely compress the rings as the pistons are pushed into the bores.
To install the rings on the piston, I use a short wrap of .001" shimstock to slide the upper rings over and past the piston's lower ring grooves - again with some oil. Other than that, I just hold my breath and spread them with my fingers to get them started onto the skirt. - Terry

 

[Cogsy]

For around 1" pistons I do the same as I've always done for full size automotive and just spiral them on. I'll probably jinx myself but I've never broken a ring using this method, full size or model. To install the piston, if they go in through the bottom I put a small taper as Terry does but this is not possible if they go in through the top so I attempt to compress each ring in to the groove with my fingernails as they are about to enter the bore - it's fiddly but can be done.

 

[Gordon]

Thanks. I have been also spiraling them on but sometimes end up with the rings sprung. For installing the piston in the bore I usually use mu home made ring compressor or try compressing the ring with fingers. screw drivers etc. This came up because I am working on an Atkinson Differential and there is a slot in the end of the bore so that the ring is not entering the bore all at one time.

 

[10K Pete]

Full size practice involves, for many applications, a bit of tube that is the same, or a couple thou smaller, ID than the engine bore and tall enough to enclose most of the piston. A shallow cone is machined on the ID of one end. With the rings on the piston it is pushed into the tube from, obviously, the cone end, piston bottom first. This squeezes the rings into the tube. With some of the piston skirt extending through the un-tapered end of the tube put the skirt into the cylinder bore and seat the tube on the cylinder block nice and square. Then just push the piston into the bore while holding the tube down against the block. Slides right in.

I've used this on little engines and engines with 5" bores. It was on the big engines I learned this and have used it with perfect success and just about all I've tried it on.

Ring expanders are much trickier...

Pete

 

[Gordon]

Thanks Pete. That works great. I just made a sleeve and inserted two pistons Works great and now I wonder why I never thought of this before. It takes a while to make the sleeve but once made it can be used on any other engine with the same bore. After a while I will end up with one of each common size.

 

[10K Pete]

Gordon, the problem with this method is that I sometimes find myself thinking that a new engine is thought of in sizes that fit already made tools instead of new tools to fit the new engine.... lazy thinking!

Pete