I have a 1987 12.5 drawbar horse power 2 cylinder Kubota diesel engine that started to over heat in the summer of 2005. The radiator has a grating with pin hole openings bolted in front and I placed a fabric screen in front of the grate before I used the tractor when it was new. I try to keep the radiator fins free of dust and debris, but it gets built up over the years and eventually causes the engine to overheat. The radiator gets new anti-freeze every three to four years as the unit only gets under 25 hours use each summer.

This fall I drained the old green coolant from the drain tap under the radiator frame and then removed the radiator. When I lifted the small radiator away from the radiator hoses I noticed a fair amount of liquid that looked like milk coming out of the radiator outlet for the bottom hose. When I looked in the radiator cap opening the top of the core looked like it had a small layer of white build up. Does anyone know what that milky white liquid is?

Right from the very first coolant change after I bought the tractor new I have always used distilled water in a 50/50 coolant mix. The anti-freeze container says: Low silicate formulation; specially adapted for diesel engines. Not recommended for non-diesel applications. Provides protection against corrosion, winter freeze-up and summer boil-over. Meets ASTM and GM specifications for diesel coolant. Contains ETHYLENE GLYCOL

 

Sounds like oil has entered the cooling system causing the milk.

I have a Kubota B7100, 3 cylinder, 17 hp. Few years back while cleaning the top of the head before adjusting the valves the top of one of the head bolts came off. Upon further inspection four of the eight bolts holding down the head had their heads broken off, they were just held on with blue paint. I never experienced any leakage or problems but did replace the bolts.

This could allow transfer of oil to coolant though.

Told my neighbor who has the exact same tractor, he found broken head bolts on his also.

 

Thank-you very much, infidel, for the information. I am not a mechanic and have had little experience with engne work; therefore, I depend on others to provide me with clues in order to know what to do to solve an engine problem. Actually, I do not know very much about mechanics of any type. I noticed the radiator is leaking at the top of the cores at the junction of the expansion tank situated on top of the radiator. The coolant level went down since the last coolant change two years ago for the first time by a couple inches. It costs $125 to recore the old radiator and $750 for a new radiator. I had the old radiator recored in my little D-50 Ram pickup and a year and a half later it started leaking again. Fortunately, I was able to buy another new radiator for two hundred dollars. The old radiator had cost me that much to recore, and all for nothing.

The 12.5 HP block's 2 cylinder head has four bolt heads on the right side in the region of the fuel injectors and incorporated intake manifold that is part of the cylinder head, and I assume the other four cylinder head bolts are under the valve cover. Is that correct? The exaust manifold incorporated in the head is on the left side, as is the valve cover. I put a 13mm socket on the four exposed cylinder head bolts on the right side and found they are solid. There is absolutely no head gasket leakage indicated on either side of the block and the valve cover gasket is not leaking any place. I suppose there may be a leak in the gasket area between a coolant passage and an oil passage. The oil level does not go down and the oil is never contaminated with coolant. I would hate to remove the valve cover and find out the cylinder head bolts are tight. The little engine has no water pump and is put to some very hard work around our yard and treed wind breaks on the farm where a larger tractor can not fit.

It has a 44 inch under belly mower deck, a 47 inch rotary tiller, a light duty hydraulicly operated dozer blade, a 60 inch wide cultivator with shovels and spikes, a 55 gallon pull type sprayer and I am fabricating a wagon for it. I had to cut both side ends off the cultivator frame with one tine on each side and fabricate attachment brackets. The tractor has four tire chains and 125 lbs front weight and it still loses traction when 60 inches of spike width is pulled; therefore, the cultivator is used with spikes and no extensions installed. The shovels can be used with the extensions installed.

 

You are correct, the other four bolts are under the valve cover. If you've owned the tractor since new it would be wise to remove the cover and check the valves if they've never been done. Mine are always off when I check them, tractor runs noticeably better with valves adjusted.

As for the milk, I would just flush it well for now and keep an eye on it.

These little Kubotas are certainly handy. Besides replacing two clutches and a set of tires I haven't had any problem with mine. Over 4000 hours on it and that is a low number as I didn't put an hour meter on it till it was a couple years old. Mainly use mine for spot spraying with a 20 foot boom when there's no need to bring out the big guys.

That radiator price certainly is impressive, my radiator couldn't be more than 2 square feet.

 

Have you had any trouble with the oil light coming on? I've got a B6200 and B8200 both bought new. The B6200 is a 1980 model. I had the oil light come on several years ago. I know the dealers family real well and was able to find out short cuts they had used for just about every type of service work.

It turns out the cam shaft had a hole drilled in the front end at manufacture which was required for tooling. The hole was then plugged with an alum. plug. As time went on the temperature differential of steel and alum. cause the alum. plug to be pushed out. If you need to solve this problem I can give you the info. so you don't even have to remove the cam!

I've had to replace the head bolts on that engine also. Just noticed one loose, and maybe one cracked in two. But the engine never gave any indication of a problem. I just happened to notice it and fixed it.

I picked up a Harley oil pressure gauge at a bike shop. They are made to be exposed to the elements. Mounted it down low on the left side by the steering sector arm. Works nice.

You can go to "yesterdays tractor" and post for all kinds of info. on just about any tractor. They're helpful over there also.

 

I have owned this B4200 since I purchased it new in the spring of 1987, and it now only has 451.3 hours on the meter. Would the valve clearances need to be re-set with such low running hours? The engine has lots of power and gets good fuel economy even better than when it was newer. At less than five hundred hours the engine is just getting broken in. The tractor engine has never been started without first the inline coolant heater being plugged in for at least an hour. That way it can start working immediately. The little Kubota only is used, now and again within four months, during the summer time. Only the storage battery has been changed about five years ago, and it is recharged every two months when idle. The engine oil and oil filter are changed every two to three years. All the gear lube and hydraulic transaxle fluid was change to Amico 100% synthetic lube and hydraulic oil about six years ago. This radiator leaking is the first major problem with this little tractor. The radiator is only one foot by one foot and is illogically expensive to purchase compared to larger radiators for other applications. It would be practical if the Kubota radiator had stiff radiator cooling fines like the John Deere articulating tractor radiator, so I could take the high pressure air compressor and blow out the debris that collects in the fins.


The tractor is stored in a shop with a concrete floor that is heated during the winter months. For the first three years that I owned the Kubota I stored it in an unheated garage with a concrete floor. Cold iron attracts the small percentage of moisture in the dry frigid air during the winter time, and it rusts and pitts unpainted ferrous surfaces. The V groove in the pulleys in the mower deck became so rusty and pitted during the winter I needed to remove the belt each spring and use a wire wheel on an angle grinder to clean up the grooves so as not to wear the belt from abrasion. The Kubota mower belt broke after four years use. I started to house the tractor in our heated shop and never once have I had to buff the pulley V grooves. The belt running in the grooves keeps them shiny. I replaced the first Kubota mover deck belt with a Kevlar stranded belt, because a replacement Kubota belt cost over $55, and that Kevlar belt has never broken. I just had to retension the belt to compensate for wear. I am replacing it this winter as it has had twenty cracks for several years and this past summer developed three, one inch to one and a half inch, missing chuncks. If the belt's V moulding was still intact, I would run it to see how long it would go before it broke. That Kevlar belt was installed in 1991 and it only cost around $25.

 

If I'm not mistaken Kubota recommends adjusting the valves every 500 hours.
You're getting darn close. The first valve adjustment is the most important on a diesel, that's when they are usually off the most. I'd do it before summer mowing season starts.

Might have to try a Kevlar belt on my John Deere zero turn mower, I broke three autoparts belts this summer. $28 each. Replaced an idler pulley bearing that I thought was causing the problem but broke another belt in less than 15 hours mowing. The original JD belt went for five years, maybe my trying to save money is really costing more in the long run.

Found an excellent source for blades http://www.agri-supply.com/
Their blades inexpensive but made in the US by Oregon, the same company that makes top of the line chain saw bars.
Might not work for you with Canada shipping though.

 

infidel, having to set the valves this winter will kill two birds with one stone. The valve cover needs to come off to set the valve clearances, and then I can check the left side head bolts while the cover is off. The problem is that I use Haynes manuals for information to work on my vehicles, but where do I find out the head bolt torque values and the valve clearance specs. for the intake and exaust valves in a little Kubota B4200 tractor?

 

infidel, I do not know how long you store your Kubotas during the off season and exactly how humid your area happens to be during that time, but if you are having clutch problems it may be from not blocking the clutch in an unengaged position while stored. My Kubota manual says: Lock the clutch pedal with the provided wooden block. If the tractor is stored for a long period with the clutch left engaged, the clutch disc may rust, rendering it inoperative. Possibly all those hours on your tractors wore out the friction disc through excessive repeated use.

 

infidel, I'am not familiar with a JD zero turn mower or its belt's mechanical arrangement. The only possible helpful suggestions I can offer is related to belt breakage on other small tractor/mower units with a clutch operated mid PTO shaft that functions at the higher rpm than the rear PTO shaft. Another thing is if a V belt is not designed to turn back on itself, over the idler tension pulley, then in a short time of use it will crack and break under stress. Is the belt tension adjustment correct? The cheaper belts you purchased may not be constructed with the intention for them to pass over an idler pulley. Your drive belts breaking in such short time could be cause from operator initiated severe stress and strain on the mower drive belt. Users are having problems from engaging the clutch and thus the PTO while the engine RPM is too high. The tractor transmission has to be in gear to start the tractor moving at the same time the PTO is engaged. To save my clutch and drive belt, I initially have my engine running very slightly higher than idle speed. The tractor clutch is engaged somewhat gently as the mower blades initially just start turning. As soon as I hear the blades instantiously start rotating I immediately increase the fuel to the engine to prevent it from stalling under the load of the blades and forward propulsion. The drive belt can withstand a progressive aggressive excessive amount of strain, but it can't hold up to the snap adding to more excessive strain from high engine torque and dumping the clutch. A Kevlar stranded belt is only about one third stronger than a standard belt.

 

Your owners manual should have the specs on the valves, mine does and even details the procedure. Doubt if it's the same for yours though.

It's very dry where I live, average 8"/year, hardly ever see rust even on equipment that's parked outside all year. I'm certain hired help and high hours are the reason for clutch replacement.

You could be right about the belts I'm using not being designed to bend over backwards on the idler. Probably try a JD belt out next year and see how it does.

 

I have looked through my Kubota operator's manual for my B4200 every year for so long I practically know where to find the information on doing any type of maintainance, but never have I seen the valve clearances or head bolt torque specs anyplace. Actually there is a Specifications Table on page seven, but the section on the engine says it is a Model Z600-A. It gives the Type, No. of Cylinders, Bore and stroke, Total Displacement, Rated Revolutions, Fuel, Starter, Cooling, Battery and nothing else on the engine. I will look up Kubota on the Internet and see what I can learn about the specs.