recommended grit to hone cast iron hydraulic hand pump bore with ball flex hone for leather cup seal?

tomjelly · Jan 2, 2023

I've got an older cast iron hydraulic hand pump, 3/4" bore, that uses a leather cup piston seal and has some galling on one side of the bore. I'd like to hone it with a ball hone to take off any rough spots in the galled area; I may do it in 2 steps progressing to a finer finish grit. What grit should I finish with for that leather piston seal to run on?

Milland · Jan 2, 2023

What about using a brake cylinder hone? Might give more uniform results than a ball hone:

https://www.amazon.com/Lisle-10000-Brake-Cylinder-Hone/dp/B0002SQUG8/ref=sr_1_1?crid=2AN4WV0FT202T&keywords=brake+cylinder+hone&qid=1672695151&sprefix=brake+cylinder+hone%2Caps%2C589&sr=8-1

tomjelly · Jan 2, 2023

That will not touch the galled area as the stones will probably bridge it. I need to resurface the galled spot, which the balls should be able to do. The dip in that spot shouldn't be an issue as the leather seal will conform. I may get one of those also anyway in case it doesn't work well enough with the ball hone.

Milland · Jan 2, 2023

Fair enough. Is there any point to reboring the cylinder, then a brass sleeve or similar?

tomjelly · Jan 2, 2023

If it doesn't come out well I might want to but would not know how to seal a sleeve at the head end against fluid going around the sleeve and coming out the packing end as there is not a separate cylinder head. (If there is a way I'd like to know how) more likely would be to bore and use 13/16 round bar for a new piston as all it has is a screw to attach the cup seal on one end and a cross thru hole on the other. for a lever pin

Milland · Jan 2, 2023

Presumably bore to depth with a few thou clearance per side, then clean everything and use a "sleeve sealer grade" Loctite or similar to coat and bond the length of the sleeve into the bore. Unless I don't have a good picture of the bore and port geometry in mind, that should work.

tomjelly · Jan 2, 2023

I used to have a bookmark for some outfit who made small sleeves, I'll have to look around, it would be nice if I could find some fairly thin wall 3/4 ID tubing with a nice internal surface finish.... Not sure what material would be suitable and I'm not sure what material the piston is made of either...

Milland · Jan 2, 2023

A call to McMaster might be worth it, if you trade your time for their higher prices. I've used thin-wall stainless steel for such things too, but I think their variety isn't as broad as it used to be.

Someone makes hobby brass tubing with telescoping fits, nominal 1/32 wall (slightly under, I'd think), might be checking that out too.

cyanidekid · Jan 2, 2023

seems like you could replace the pump for less than the cost of 2 flex hones

tomjelly · Jan 2, 2023

This pump is built in to a larger casting, If I recall correctly a $400-$700 part. Yes, some thinwall stuff would be the thing as it is well supported all around

hvnlymachining · Jan 2, 2023

In ball hones, rough with 120-200. Finish with 500 or better ( I prefer 800 when available) I much prefer solid adjustable hones when I can use them, but ball hones have their purpose. Honing oil home formula is 2 parts diesel to 1 pt hydraulic oil. Keep it flushed out well and it'll cut faster.

Garwood · Jan 2, 2023

+1 for rigid hones.

For rigid honing hydraulic cylinder bores I use 220 stones to get the ra finish needed.

I recently had the joy of honing 10 thou out of 4" sintered iron bronze bushings. I tried lots of different fluids and discovered aerosol tap Magic was super. Cut about 5 times faster than wd40 or an oil/solvent mix similar to your diesel/ hyd fluid.

I have sleeved brake master cylinders using thin wall honed steel tubing. I used no sealant, just a press fit.

eKretz · Jan 3, 2023

The original Sunnen honing oil was some funky smelling stuff but worked a treat every time I used it. Pretty sure it was packing some form of animal fat like lard as an ingredient. I too would be more inclined to use a rigid hone if possible, so as to knock down any material sticking out into the bore. A ball hone will do that eventually, but not nearly as well. I've got a couple old sets of (one is Aamco, one is Blue Point, IIRC) lifter bore "hones" in various sizes that I sometimes use for smaller stuff like this, they're double tapered parts with a sort of half wrap of abrasive cloth. They work pretty well for such stuff.

tomjelly · Jan 3, 2023

Any source for that thin wall honed steel tubing? I may run a pass with a ridgid hone for any projections before ball honing to get the low spot

metalmagpie · Jan 3, 2023

I always heard that the reason they still use leather pistons in hand pumps is that they are tolerant of things like galling.

eKretz · Jan 3, 2023

Maybe slightly more tolerant. A raised gall or even a gall that's been knocked down into negative space only with sharp edges will still roach any seal I've ever seen in short order. I think the rigid hone, then the ball hone is a good approach if the gall can't be completely removed.

cyanidekid · Jan 3, 2023

eKretz said:
Maybe slightly more tolerant. A raised gall or even a gall that's been knocked down into negative space only with sharp edges will still roach any seal I've ever seen in short order. I think the rigid hone, then the ball hone is a good approach if the gall can't be completely removed.

yup, for finishing, the fine ball hone, or much cheaper and quite effective, fine scothbrite wrapped around a wood dowel. works well up to 3" or so

Milland · Jan 3, 2023

If you don't want to try McM, you can contact Microgroup and see if they have any stainless seamless tubing in sizes like this: 13/16″ .028 .757 F10812X028 SL 304 SL316 [SL is seamless] in stock in less that full lengths, or a distributor that would sell it. Won't be cheap, but will be "permanent".

Check here for other sizes that could work, search the ID and OD. You have to skip around due to how they organize sizes: https://www.microgroup.com/products/metal-stock-custom-tubing/fractional-tubing/

tomjelly · Jan 3, 2023

Yes, the seal works, but I can see that it won't last very long as it is, a permanent fix is needed. I'll check out those suppliers. Mcmaster is fine, I looked a little there also but haven't found something suitable there yet

Milland · Jan 3, 2023

tomjelly said:
Yes, the seal works, but I can see that it won't last very long as it is, a permanent fix is needed. I'll check out those suppliers. Mcmaster is fine, I looked a little there also but haven't found something suitable there yet

Call them and give your size/material specs, let them search for options.

recommended grit to hone cast iron hydraulic hand pump bore with ball flex hone for leather cup seal?

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