Hydraulic piston to bore clearance...

[Any Cal.]

I am in the process of renovating an ooooold power hacksaw, and it uses a hydraulic blade lift. Basically, two pistons lay in their bores in oil, when one goes down it is supposed to push the other up.

I was hoping that they would work to an extent, even though the bore is quite sloppy, but that is really not the case...

I would like to fix the problem, and am looking for help with a solution. I would like to groove the pistons for o-rings, and wondering if that would be a decent solution, or extremely short lived. Any thoughts? I am afraid that the uneven bore would work poorly with rings of any kind, and I am not sure how I would hone it out.

[BethelHntr]

My dad had one years go that worked pretty good, I admired all the moving parts and sounds while cutting through a chunk of steel.
If memory serves me there was a release lever for that oil bath system that released the upper portion of the saw after the cut was finished, Have you found that? Maybe it's stuck in the open position?

[Any Cal.]

Yeah, there is a check ball that can be released, but it is seating fine. I ran the saw for a while, it looks like everything is functioning, but I am losing a good amont of piston stroke due to oil going by the sides of the piston rather than pushing it up. The piston should move a 1/2", but it barely moves an 1/8".

[Nobade]

Do you have any local hydraulic shops available to you? Perhaps a section of honed tubing could be bought to re-make this system. As for piston clearance, usually .003 - .005 is about right. If the bore is rusty or rough it will tear up any seals in very short order.

-Nobade

[jmorris]

I have built/rebuilt a few different cylinders. I use quad seals instead of o-rings. I have only machined new pistons for ones that were not made of metal and had fallen apart or for one I made from scratch.

If it worked before the seal failed it will be fine. Hydraulic pistons do not come in contact with the bore.

[Multigunner]

The proper method for truing up the bore of a high pressure pump or hydraulic cylinder is ball burnishing.
A hydraulic ram forces a precision ground ball bearing of the correct size through the bore, rounding it out and squeezing down any imperfections.
The method was adapted to finishing out target grade rifle barrels, the burnish surface of the lands not gathering metal fouling like a regular bore would have.

Don't know if this sort of service is available for repair work.
An old family friend has his own repair service for heavy equipment, but I haven't seen him in decades and don't know how to contact him these days.

[Any Cal.]

Lots of good info. There is no seal, it relied on the fit , of piston to bore when new. It was run without oil for years, so the piston and bore are now quite sloppy.

[BethelHntr]

Lots of good info. There is no seal, it relied on the fit , of piston to bore when new. It was run without oil for years, so the piston and bore are now quite sloppy.

A few pics might be helpful.

[country gent]

Another thing is what wieght oil are you using? Thin lighter oils flow thru gaps faster and easier than thicker grades do. An oring may provide to much friction causing saws feed to be sluggish

[W.R.Buchanan]

If the cylinder is not too big you can hone it with a Brake Cylinder Hone and smooth it out.

That will leave a finish that a new O ring can seal on.

I recently did some aluminum bores that had a bunch of crud built up in them, and I used a 1" dia Flapper Wheel on them. The wheel was about 1.030 in dia so it actually did flap (compress) so to speak..

The result was a nice cross hatched finish which solved the problem nicely and didn't take very long to do. In fact since it was aluminum it took about 15 seconds of back and forth motion to do each one. A steel cylinder might take a minute of effort to complete.

Randy

[Frank46]

If you decide on using o-rings get the viton ones. They are made for use in oil. Did a lot of mechanical seals way back when. regular o-rings will expand and become useless. Frank

[Any Cal.]

I think I will give the orings a shot. Good call on the Vinton, I had completely forgotten about that.

The brake hone is a good idea. I was thinking of trying to find a 1.25" reamer on eBay, but those don't come cheap... Maybe that if the orings don't work, along with new pistons.

I did cut a 2" x 4" piece of steel with the saw, and it seemed to be acceptable, but the blade lift just sort of lightened the blade pressure, it couldn't actually lift it... using the old blade until the lift is working properly. Working on building another machine, so have some immediate use for this one to cut parts...

[leadman]

I worked on alot of hydraulics and most of the cylinders had several sealing rings, both round and quad. Our system worked around 3,500 psi though.
We had our own cylinder rebuild shop and they would hone the cylinders in an old WWII lathe designed to make cannon barrels.
You should be able to do something similar or even as mentioned the flapper wheel. If you need to get the pistons cut for o-rings have 2 cuts made if possible. Then try one o-ring and if it allows oil past install the second seal. Do this as the o-rings add to the "sticksion" of the piston in the bore.
If you have a hydraulic shop nearby they might have something to help you out. Our cylinders usually had a backer made of nylon alongside the o-ring to help it stay in the groove and keep crud off the sealing surface.
Good luck.