kubota B20 water pump replacement

[misterfixit1967]

1990 Kubota B20 water pump bearing let go today taking out the last core of the radiator with the plastic fan. Need to get some tips on removing the radiator. Remove hood? Remove bottom orange support for hood? Planning on cutting the lower hose since it's hose clamp is totally inaccessable. Any more hints? Pictures? Diagrams?

Bob

 

[dfkrug]

Bob, since you don't have a parts book, you can go to Messicks.com and view the
PDF file for the radiator and related pages, no charge.

My B21 was not like your B20, but I suspect you have to remove the hood
and grille to get to the rad support bolts.

 

[troutsqueezer]

http://www.tractorbynet.com/forums/parts-repairs/185242-kubota-b21-waterpump-replacement.html

This is a reference to a B21 waterpump I replaced. Don't know if it will help. I did not remove the hood but having removed it later when I did some restoration work, I realized I should have removed it for the water pump replacement because it was pretty easy to remove and gave me all kinds of room to manuver.

 

[azbinder]

Just having done this a few weeks ago, remove the hood and grille assembly as a complete unit. Disconnect the wiring at the lights. You will then have to work the hood assy forward and up. It can be done, just take your time. I then pulled the radiator by removing the two mounting brackets from the frame. Also, I would recommend the the belt be replaced at this time as it will be a lot easier. You will have to disconnect the front hydraulic pump and move it about 1/2 to 3/4 inches.

 

[misterfixit1967]

Thanks for the replies. We did remove the hood and bottom cover by sliding the hinge pin out first (remember to leave the fel up so the pin can come out). The radiator was trashed. A new one cost $860 so we decided to get the old one recored for around $250. It will be done in a few days. Still trying to find the water pump locally. Again thanks for the help!!

 

[troutsqueezer]

I would take the old one with you when picking up the new one for comparison purposes.

 

[dfkrug]

A new one cost $860 so we decided to get the old one recored for
around $250.

Yes, you can have rads built from scratch for way less than the cost of a new one from
the manufacturer. Also, look for rebuilt water pumps on the web. We recently found
a rebuilt wp for a Deere for about 1/3 of new ($80 instead of $250).

 

[misterfixit1967]

I'm beginning to wonder just what caused the fan blade to contact the radiator. I mounted the water pump in a vice with pulley, spacer and fan blade attached and measured the motion of the blade tip as I cocked the shaft in the pump. Total motion was around .080 inches at the blade tip, which means the fan blade tip can move .040 off nominal center. I find it hard to believe that the clearance between the fan and the radiator is such that a 40 thousands of an inch slop could have caused such a catastrophic failure. Does anyone know what the nominal spacing between the radiator and the fan is? I can't measure it now since the rad is in the shop being re-cored. I certainly will measure it when the radiator comes back. The water pump bearings are not noisy and other than some slop as measured above works well and does not leak. I'm thinking maybe the motor to radiator spacing has changed?? Broken mount somewhere?? The radiator mounts were tight and all seemed well when my son disassembled it. Any thoughts or clues out there? . . . :confused2:

 

[radioman]

most likely a stick went in and out when you didnt know...

 

[misterfixit1967]

possible but unlikely. We were moving dirt and gravel on the lawn when it happened. No sign of sticks or stones in the fan shroud area on disassembly tho. . . . . :confused3:

 

[dfkrug]

Broken mount somewhere?? The radiator mounts were tight
and all seemed well when my son disassembled it. Any thoughts or clues out there?

The B20's engine is bolted to a "mainframe" and the tranny tunnel, etc. There are no engine
mounts like you would have in a road vehicle. The forward subframe that supports the rad, etc,
is also rigidly bolted.

What likely has happened is the ball retainer inside the w/p bearing has broken. This
allows the w/p shaft to spin freely most of the time, but in certain dynamic side-loaded
conditions, it can wobble enough to hit your rad. It's happened to me on a car once.

You may want to take the w/p apart to confirm this, tho some w/ps are difficult to
disassemble.

 

[misterfixit1967]

Well Katrinka is once again back in operation at a cost of $275 for a recored radiator, $115 for a water pump and gasket and $25 for a suction fan. We did remove the hood and lower hood support to gain access to the hardware and hose clamps. Hood removal is pretty straightforward, loosening the setscrew in the middle of the hinge rod, then driving the rod out with a long drift pin. Then lift the hood off and set it aside. Then remove the bolts that hold the lower hood support and pull upward and forward, clearing the hydraulic cooler lines.

We believe we have found the reason for the failure. Altho the new fan blades are three quarters of an inch away from the radiator core, the tip passes the shroud at the 6 o'clock positon, clearing the shroud by a less than a quarter of an inch! That's right, the tips of the fan actually travel BELOW the radiator core! The tip of a blade is almost an inch below the edge of the bottom tank's seam with the core.

I put the water pump in a vice and used a dial indicator to measure the movement of the tip of a blade as I forced the water pump impeller back and forth, the shaft moving in the worn bearings. The max movement of the top of thee blade was .080 inches. That would mean that in a static condition the blade would be around an eighth of an inch from the shroud. Dynamic conditions are different since the fan is sucking air through the radiator and as Newton's law says, "for every action there is an equal and opposite reaction" meaning that the flexible nylon fan is pulled towards the radiator!

We discovered another factor. The bottom of the radiator is mounted to the frame using rubber donuts thru which passes a 14 mm head bolt. When examined carefully the mounts were locating the radiator as close as possible to the fan as it could be. Loosening the bolts allowed the radiator to be placed another 1/8 inch from the fan.

The bottom line is the failed bearings in the water pump allowed an already close fan blade to touch the shroud when combined with all the other factors mentioned. The final failure occured when the fan blade actully hit the edge of the shroud, deflecting it towaards the radiator. Once on the wrong side of the shroud the blade was bent inwards toward the radiator and ultimately wiping out 6 core tubes where they enter the lower tank.

Since Katrinka is such a beautiful machine with only 800 or so hours on her I decided to go for a recore rather than a repair to the old core by soldering off the core tubes and filling in the holes left in the lower tank. I also went for an OEM pump rather than an aftermarket pump which would have been around 30 dollars less.

Warning!! Loosen your fan belt and check for play or slop in the water pump shaft!! Remember there was no noise and no leakage, just sideways movement of the pump shaft and a catastrophic and expensive failure!!