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Thompson Grinder and Antique Hydraulic Seals


Jun 24, 2016
I'm working on a Thompson Grinder Model "F". This model of grinder was made from the early 50's to the early 70's. I think this is an early one. It developed vibration in the table feed so I took the hydraulic table pistons apart. Some of the seals were broken or missing.

The pistons have u-shaped vented metal shields. I have not been able to find any information about these or find anything like them. Anyone know anything about this style of seals?

If I can't find them I think my alternative is to make/modify the pistons for a more modern seal.IMG_9228.jpgIMG_9227.jpg
I was about to toss a Thompson Model F surface grinder manual. PM me if that is something you'd be interested in and I'll send it to you for the price of postage For future manual seekers, I do have a scan of the manual so PM me me if you want a copy.
Cast iron rings aren't too uncommon in older hydraulic machines, especially anywhere heat might become an issue for other seal types that existed back then.

That said, there are far better options today that pretty much eliminate cylinder barrel wear. Bronze filled piston seals can resist high temp and with less friction than those old cast rings. U cup seals may wear a bit too fast in that application, so avoid those.
Be sure to hone or polish the cylinder before reinstalling that piston, a fine ( min 400 grit) cross hatch finish will greatly increase the life of the repair.

I also see dings and chips on that piston, be sure to buff any rough spots and check for loose metal fragments. Also inspect the barrel, you likely have some scarring in there that will need attention.

Side note, be sure none of that cat hair gets in there! It's incredible how much trouble a little hair can cause in valves.