Ask the Mechanic

Blown Rings

(Progressive Farmer image by Steve Thompson)

READER: I have a little B7100 Kubota tractor that has become hard to start. It has glow plugs, but I'm not sure they work. My son borrowed the tractor and has been using starting fluid to start the engine. He tells me that it now blows blue smoke out the exhaust, and a stream of oil runs out the breather pipe, especially after the engine gets warm. What could be wrong with the engine?

STEVE: I am sorry to tell you that your engine will need an overhaul because of the use of starting fluid on it. The glow plugs will allow the engine to start very quickly, and you should never use starting fluid on an engine with glow plugs. This engine is what is called an indirect injection diesel, which means the head has a small concaved area made in it that allows this area to become very high in compression, because the indented area traps and raises compression in that small area when the piston comes up on the compression stroke. Plus, Kubota puts the tip of the glow plug (which gets red hot) in this concaved area, and the injector sprays fuel directly onto the red-hot glow plug. This combination allows for quick starting after the glow plugs are hot. The starting fluid is just too powerful of an explosion and has blown the rings out, and probably damaged the lands, or the area between the rings on the pistons.

READER: I have a Ford New Holland 555E backhoe. My problem with the machine is that it has to be jump-started. I had the starter checked three times and finally replaced it. The replacement starter did not improve starting. I replaced the battery and cables, and I still have to jump-start it. Can you tell me what else I should do to make the tractor start?

STEVE: You should check the compression on the diesel engine next. The compression ratio on this engine is 17.5 to 1, and the compression should be 420 to 510 pounds, plus or minus 50. The Ford diesel engine runs high compression, and it needs to be in specs for starting. Have the compression checked, and if it is within specs, then I would think the injector pump is not going into start position to deliver excessive fuel for starting.

> Write Steve Thompson at Ask The Mechanic, 2204 Lakeshore Dr., Suite 415, Birmingham, AL 35209, or email


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