Hi everyone, I suspect this is a one word answer type deal but here we go. I've got a Bobcat t190 track loader/skid steer that I've been chasing a dripping track motor with lately. It is also behaving slightly oddly, at really low speed I get lumpy power from that side but otherwise it is perfectly useable. High speed is fine, (maybe flies slightly crooked) but good power pushing etc. I did find a leaky fitting and thought I'd got lucky but after still seeing a leak I decided to tear it down and look. All looks perfect, other than this one wear spot on the distributor. I've never really seen the inside of one, so I wonder what the experts think of this, is it toast? I can't feel a difference with my finger. At first I thought I'd get a seal kit for the unit and put it back together and get on with it. The machine is set to live the retired life with us, maybe 50-100 hours a year. But the more I look at it I think this is exactly where my lumpy power problem is coming from. And actually, the lumpy power is trivial I'd still run it if I wasn't worried about it making metal and wrecking other components. The filter was clear of any brass or metal. Maybe not a one word answer but I'd love to hear some thoughts. Thanks in advance! Josh
It looks to me like the plate is warped. Possibly it warped before heat treatment and when finish machined didn't clean up all the way. Just SWAG from a photo, ymmv.
I'm sure someone else with more experience/knowledge will chime in but from what I have been told, you should be able to polish that out with a flat plate and some fine emory paper. Polish until all of the lines disappear. Use a figure 8 pattern to ensure a perfectly flat surface and even polishing. Make 100% sure that everything is spotlessly clean prior to reassembly. Last thing you want is abrasives in the hydraulic system. Maybe it is too warped to salvage but if you have the time to try this, it might make it better without a lot of cash outlay. I've seen much worse valve plates that were still pulling pretty well. I'm sure these low spots are causing the stutter as the pistons lose pressure over these deformed areas.
Does reducing the dimensions of the entire valve plate not cause the entire thing to leak? I don't remember taking any notice if this is pushed onto the mating face by any force or if it purely relies on tolerance of the housing. What sort of grit would you start and finish on? It is harder than holy hell. I centre punch marked the housing sets to get the same holes aligned up in case I reassembled and the attempt on this section broke the centre punch prick off xD. Thanks for the reply I'll look into it
Seems they do exactly that. I found someone nearby with a lapping table, wish me luck
One thing that still has me stumped is if you remove say .0004" off the face, how do you take up that gap when reassembling?
Shims if they don't fall within specifications. Download the rebuild manual if you can find it online and read up on the assembly process. Most hydraulics that I've read about or worked on have shims for bearing pre-load and to take up on manufacturing variances. 4 tenthousandths of an inch (what you have written above) is next to nothing. 4 thousandths of an inch (about the diameter of a human hair) might require a shim but doubtful. 40 thousandths will need a shim pack if it is within tolerance to use the part. That much might scrap the parts.
If that part is hard it will take hours just to lap .0004, weeks to remove .004. .040 is not possible lapping by hand in this lifetime. Prolly just needs replaced.
Yeah, would need a surface grinder and maybe lap after. I can't imagine a skid steer drive motor is fussy to 0.0004" but I'm not an expert.
Ha, most mills won’t even hold .0004 thou. I have used a fly cutter to face a few hydraulic valve plates and they came out nice. A lapping table makes them perfect, or as perfect as can be.
Just to update here for what it's worth, I ran the part down to a guy with a lapping table and he found a gouge in one of the pistons, said it looked old, each piston might be bypassing ~10%, add it all up and there's no use refacing. The gouge in one of the pistons was the nail in the coffin. I got a new rexroth unit (ouch..) Decided I'd better pull the other track off and check while I had it up and found a near new track motor there so, delighted with that at least. It's all holding strong, have stripped a 7000sqft pad for our sawmill this week, it must've moved about 250m3 of topsoil. Thanks for the help here appreciate all the comments
Thanks for the update.