What's new
What's new

Mori MV35/40 Daikin pump noise & Taiyo hydraulic spindle counter balance seal blowout


Apr 23, 2005
Mori MV35/40 Daikin pump noise & Taiyo hydraulic spindle counter balance seal blowout

It all began when my hydraulic pump started making noise after letting the machine sit to long.
Often when using the machine regularly, the hydraulic pump would make some noise at startup then quickly go away, this time it wasn't going away.

I pulled the hydraulic unit from the machine and disassembled the pump, looked it over for contamination and damage, individually purchased new seals and bearings, then reassembled.

-Does anyone know a domestic supplier to get a new axial cylinder and piston assembly for a Daikin V15 axial piston pump?
-Has anyone retrofitted a comparable open circuit pump (Parker, Rexroth, etc.) with approximately 15cm3/rev (0.90 in3/rev) output
that is pressure and flow adjustable, from 8-70kgf/cm2 and up to 27 lpm @ 1800 rpm (114-996 psi and up to 7 gpm ) and CW
rotation, to replace the Daikin unit?

At that point, being overly anxious to see if the noise was gone, I neglected to lower the operating pressure and/or flow of the pump when restarting the machine, for now there was air in the system, and proceeded to blow out the rod and wiper seals on the spindles hydraulic counter balance cylinder. Causing hydraulic fluid to pour from the spindle covers, once the spindles internal voids, having been well sealed by decades of chips, coolant and oil, finally over flowed.
Seems its now time for the coolant system, tramp oil removal project I've been putting off.

Upon disassembly of the counter balance cylinder I noticed the cylinder had been operating with some degree of side loading and had worn the brass/bronze cylinder end cap insert, that houses the rod and wiper seals, and to a lesser extent scuffed the cylinder rod as well. Probably leading to the hydraulic seals blowing out due to the air compressing in the cylinder from hydraulic oil entering at high pressure and flow.
At that time I also noticed the piston that drives the cylinder rod had what appeared to be (2) ring lands, with a "V" shaped profile that I would have thought would have seals in them, for sealing the piston to the cylinder bore, but there was nothing in them. The lands are approximately .080 inch wide and 0.60 inch deep to the bottom of the "V" groove. I'll disassemble the rest of the cylinder checking the piston-to-bore clearance as well as check the vented end for lost seal remnants.

-Is it possible the piston works without seals in the "V" grooves and not leak out the filter vented end of the cylinder?
I've been unable to locate a parts breakdown of the counter balance cylinder.

As a note the counter balance cylinder has only (1) hydraulic line on it so it is a single acting cylinder with a filtered vent, opposite the end with the hydraulic line. With no evidence of hydraulic fluid escaping the vent or of the vent being plugged up. I also witnessed hydraulic fluid spraying from the seal end of the cylinder when the pump was running noisily. Could be the large leak from the cylinder seals was causing my pump to cavitate noisily from an inability to keep up the flow demand.

-Has anyone had luck finding parts for the Taiyo 70H-6, type 1TC40C70N550-B0 counter balance cylinder? Specifically the
brass/bronze insert that houses the seals. I think the cylinder rod will polish up ok in the lathe with some 1000 wet/dry.

Upon cleaning parts I found no large debris in or stuck to the large magnet mounted in the bottom of the hydraulic tank, just a fine sedimentary layer across the bottom. At some point in the last 40 years I believe the Daikin pump had been replaced because it did not have the same color or durable Mori green paint on it.

My conclusion on the pump noise is either the counter balance cylinder began leaking, to a lesser degree than when starting the machine after sitting for a couple months, or there is a relief valve/control solenoid leaking/stuck for the counter balance cylinder.
I've come to that conclusion because after the seals blew out on the counter balance cylinder, I removed the hydraulic line to it and capped it, before positioning the spindle to remove the hardware affixing the sheet metal spindle covers and counter balance cylinder.
With the machine running the hydraulic pump noise was gone.

In a couple days I have replacement seals arriving for the counter balance cylinder and I am hoping with new seals, the worn cylinder seal insert assembly and rod will hold, after some rod cleanup and realignment.

Does anyone know of a Daikin parts supplier in the states?
and/or a comparable replacement pump?
Could the counter balance cylinder really run without piston seals ... Has anyone seen hydraulic piston seals that fit a "V"
I don't suppose anyone has a parts breakdown for the Taiyo counter balance cylinder?
Or has run into an alignment problem with it.

I will return with more details upon further disassembly.

Vancbiker ... SeeFair ?
I'd try here for parts and info....


I've never taken apart one of those cylinders so no idea about seals. IIRC they were originally set up from the factory with a self aligning coupler on the rod to reduce alignment trouble.

Pumps are are pretty easily interchanged. Some of them had splined input shafts so getting a matching spline from another manufacturer might be troublesome.

IME, the most common cause of start up cavitation is a clogged inlet filter or an air leak at a fitting or a cracked tube/pipe.
The cylinder rod is threaded into a substantial steel block, jam nutted, and the block bolts down to the z axis by way of (2) socket headed cap screws (SHCS), just behind the spindle drive motor.
The cylinder itself mounts to the frame of the machine by way of trunions out either side of the cylinder, 8 or so inches from where the cylinder rod protrudes out of the cylinder. Then separate steel blocks slide over each trunion, each with (2) SHCS and the assembly bolts into a recess on the frame. Effectively capturing the trunion blocks from above and below eliminating the possibility of any vertical movement working the SHCS loose.
No alignment coupler and trunions have no bushings or bearings so alignment would have to be by way of shims behind the trunion blocks or elongating the block threaded onto the rod.
The hydraulic pump shaft, 3/4" with 3/16" keyway, slides into the end of the motor shaft.
When I disassembled the hydraulic pump unit there were some questionable pipe joints, seemed a little loose to me. The suction strainer was clean with no visable debris stuck to it.
Oddly the pump noise completely went away after I capped the hydraulic line to the counter balance cylinder, and powered the machine for repositioning before disassembly.

Thank you for your time,the parts link and the information.
I showed my parts to a hydraulic cylinder friend and I ended up learning more. In front of those "V" groves, near the top of the piston, there's a bronze ring 5mm wide or so. Turns out that is a sealing ring comprised of Teflon and bronze with an o-ring behind it to tension the ptfe/bronze ring against the bore.
If I can find one the right size I'll see about replacing it, sounds like they are a chore to install into the ring land. It involves heating in oil, above 212F, to soften then wrapping in protective tape and compressing the stretch out of it.
"Sounds like I better buy 2" .... Words I live by ...
I wish that's what it had. I've noticed there were several version changes to the machine over the years. For instance my'84 machine has the short 18".... "enclosure" around the table while I've seen later models the enclosure is full height and tips in at the top only leaving a small portion of the top open.
. I'll snap some pictures tonight of everything.
Might be possible that it had one at one time and was broken and removed. You are correct though in that during the production run of any machine minor changes are made. Full enclosure was an option, but not often bought as it was very expensive. Expensive enough that I saw a handful of machines get locally built full enclosures added after delivery.
I showed my parts to a hydraulic cylinder friend and I ended up learning more. In front of those "V" groves, near the top of the piston, there's a bronze ring 5mm wide or so. Turns out that is a sealing ring comprised of Teflon and bronze with an o-ring behind it to tension the ptfe/bronze ring against the bore.
If I can find one the right size I'll see about replacing it, sounds like they are a chore to install into the ring land. It involves heating in oil, above 212F, to soften then wrapping in protective tape and compressing the stretch out of it.
"Sounds like I better buy 2" .... Words I live by ...

Don't know if these guys have presence in Washington; H&D Distributors. Guys I talk to can almost always get the correct seal from my description of part to them. ID, OD, Ht, mat, style, backers, etc.
So I've got the counter balance cylinder back together, I'm just working on cleaning up the spindle area before reassembly. I'm attaching some pictures of the counter balance mounting situation, I'll update again when I figure out how I'm going to fix the mis alignment of the counter balance cylinder.
On a separate note, I have a new appreciation for the retired cnc repairman here. Nearly 40 years of filt under the covers of this machine, I can't leave it like that.
I can't imagine going to a repair job and having to install parts through all the chips, oil and coolant that gets cemented solid with dust.
I've spent days trying to remove the dried on crud. It impresses me even with all that trapped between the covers that the rust is so minimal. The paint Mori used on these machines is something else. That and how solid this machine is, it reminds me why I chose a machine so old for my first cnc. At more than 15,000 lbs, I've read that's almost 2x as much as some of the modern cnc machines made today, for similar X,Y,Z and HP capabilities .. One solid piece of iron.

Edit .. I'm having trouble getting the file size of my pictures small enough to attach .. Let me see if I can find a better way
That's normal gunk. Some outfits use heavy airblast to blow steel chips out. Chips get blown everywhere. It can be like putting your hand into millions of tiny razor blades. Gloves are useless. You just do it and cut the slivers out as they fester up over the following weeks.

I have bought several machines that way. I got about 90% off their market value, but I paid for that in other ways.
Here's those pictures


I had a heck of a time getting my iPad pictures small enough to attach and the file size in the app I used, didn't correspond well to what the forum says the size is.
They ended up smaller than they needed to be.

first picture is where the block the rods attaches to, mounts to the Z axis behind the spindle motor and in front of the Z axis servo motor (upper portion of the picture you can see one of the trunnion blocks).

Second picture is one of the trunnion blocks that attaches the top of the counter balance cylinder

Third picture is the block attached to the cylinder rod

and the fourth picture is the cylinder with the second block on the trunnion
Struggles continue

I finally got everything together enough and clean enough for some adjustments. I think Ive got the counter balance cylinder aligned better than previous installer had it. Now I'm struggling with the manual on adjusting the hydraulic relief on the counter balance.
The manual that I got with the machine references a non existent terminal block to measure the current draw on the Z axis servo for adjusting the hydraulic assist from the counter balance cylinder. I think I get the jist of what the adjustment is supposed to do but the relief adjustment only really affects the Z+ direction. Here's snippet from the manual on the adjustment


  • Screenshot 2022-04-12 at 8.24.37 AM.jpg
    Screenshot 2022-04-12 at 8.24.37 AM.jpg
    17 KB · Views: 10
I assumed as well .. Picking 1 of the leads on the Z axis servo amp going to the Z axis servo. The translated from Japanese manual, speaks of setting the relief valve for the counter balance so there is -8A to +9A swing on an inline ampmeter. I figured a 9A draw on the servo when the cylinder is assisting the up travel and an 8A draw on the down on the down stroke.
Only there's more draw on the servo in the down Z travel than the up Z travel. Aren't I looking for the opposite? 9A load when Z is traveling up and 8A when the Z is traveling down. No matter how I adjust the relief valve there's always more load traveling down against the hydraulic assist from the counter balance cylinder. I guess I'll set it so they are about balanced. That seems to make more sense.
. Any ideas what this adjustment is really trying to accomplish?
"Any idea what this adjustment is trying to accomplish"

To clarify my question .. A counter balance Is to minimize wear on the ball screw and balance the travel.
If that's the case wouldn't the goal be balanced loads on the servo and even wear on the ball screw?

When I adjust the relief valve to balance with the reducing valve it ends up around 7 to 7.5 A
"Any idea what this adjustment is trying to accomplish"........

A major part of the counterbalance function is to reduce the constant current draw on the motor when the axis is static. If you watch the current with the reducing valve set to a low pressure you will see a fairly high constant current draw. As you increase pressure the draw will go down. If you raise the system pressure too high then the motor will be working against the counterbalance and current (reverse) will start to climb.

Somewhere in the late 80s to very early 90s Mori stopped using counterbalances and just equipped the Z axis with a power off activated brake to keep the axis from dropping. This tells me that screw wear is not the main consideration for using a counterbalance, but dealing with heat build up was. It seems like the change happened right about the same time the switch from DC to AC servos occurred.
Yeah the heat generated from this machine is noticeable, a dozen fans I can think of off the top of my head in this M35/40, vintage 1983 or 84.
The servo works harder against the counter balance at almost any reducing valve setting. So much so I can't believe there isn't a adjustable relief valve in there also. No matter how I adjust the reducing valve I can't get the current loads on the servo better than balanced.
I did notice a half amp draw from the servo while static, machine has AC servos.
The hydraulic pump makes more heat than the Z servo and controller combined.