B7200 oil blow by

[Anonymous Poster]

I have a B7200 HST. At high RPM,S the engine oil runs out of the crankcase breather tube. Any thoughts as to the problem and the remedy. Complete re-built engine will cost more than the worth of the tractor. Can I do an in-frame overhaul on this tractor. What are the chances of getting by with a ring job. This tractor has been run hot in the past. :crazy:

 

[Kelvin]

JDHG,

This topic has come up a couple of times already this year. Like my responses to other posts, I'll give you my war story.

Shortly after purchasing my used B7100D (16hp; 4wd; gear drive), it starting exhausting blow-by smoke out of the valve cover breather tube. A short time later the smoke turned into oil droplets, then the oil basically poured out of the tube.

Defect: Two of the three cylinders had bad compression rings. The cylinder closest to the radiator was in good shape; the two furtherest away from the radiator contained the defective rings.

Primary Cause: I suspect an overheated engine caused the defective rings to weaken based upon their location relative to the radiator.

Secondary Cause: Again, I SUSPECT that at the time of purchase 100% antifreeze was used in the radiator, which can be very damaging to thermo-siphon type pressurized cooling systems. I do not know if the B7200 has the thermo-siphon system or whether is has a normal system with water pump and thermostat.

Fix: The engine was never removed from the tractor. The head and oil pan were removed. Pistons were removed. All engine components were in excellent shape except for the compression rings. I replaced the rings and rod bearings and honed the cylinders. The crankshaft (main) bearings were not replaced. I had the head rebuilt (new valves and valve guides & seals)since I had it off, even though it gave no indication of wear. Put it all back together. That was 1997 and it has worked fine every since.

Good luck,
Kelvin

 

[sandyc]

My suggestion is to pull the injectors and take a compression reading. I don't know what the specs are but the readings should be within a few percentage points of each other. If one cylinder is low then what I used to do is squirt in motor oil and take the compression reading again. If it comes up after the oil is squirted in then it is a ring(s) that is the problem. If it still doesn't come up (the compression, that is) after the oil squirt method then you could assume the valves or valve guides are shot.
Just some thoughts....good luck!

 

[Anonymous Poster]

Can you give me an idea as to the cost of the overhaul on your tractor. The approach you laid out is about what I had decided to do.

 

[Kelvin]

JDHG,

It cost me around $1000.00, parts & labor. Without going through the trouble of finding all the receipts, it seems like parts cost around $600-$700 of that total.

Parts: Any Kubota part that I wanted was available. The parts were more expensive than what you'd expect, but survivable.

Labor: I have access to a very reliable automotive shop that performed most of the work for me at a reduced labor rate, since I help keep their computers up and running when I am not out playing on my tractor or flying airplanes. Rebuilding the head at a machine shop cost normal full rates.

Hope this helps,
Kelvin

 

[Kelvin]

From my shop manual for the B5100/B6100/B7100:

"Compression Pressure - All Models

Compression pressure should be 398-454 psi. Allowable minimum pressure is 341 psi."

If I remember, the B7200 engine is slightly larger than the 16hp B7100 engine, so I would guess that the compression specifications would be similiar.

Kelvin