In 1893 Rudolf Diesel designed and built his first diesel engine. It was a rough starting and running design that refined through the years to the reliable, smooth, quiet and easy starters that we have today. All fine until something wears out.
Everyone who works with diesels has their favorites. Mine just happens to be orange with a 17 hp three cylinder diesel, straight forward, no bells or whistles and dependable. My Kubota B7200 1985 vintage has a glow plug controller on the dashboard that coincides with the key position for pre-start heating. Pre-start heating is an actual element that gradually glows brighter as it heats up giving an indication when it’s the correct time to turn the key. It’s a slick system that until now has worked like a Swiss watch. I noticed a hesitation and puff of black smoke when engine starting and found the cause to be a timed-out glow plug.
The only maintenance to glow plugs is to ensure that the wiring is clean and tight. That’s it.
When it stops glowing, replace it.
Diagnosis
Without the luxury of sensors that tractors and just about everything else today has, telling you what the problem is and where to find it, means that I had to determine which glow plug was to be replaced. There are three ways to do this. Before rolling out the tool box, if your tractor has a fuse in the preheat system, start by checking it first. This is a good one to remember for maintenance in general as a lot of the new tractors are servo operated. Instead of moving a lever by hand to engage a particular drive you flip a switch and through an electrically operated servo that drive is engaged. A good friend of mine got caught diagnosing a faulty PTO; he spent four hours trying to find the mechanical problem finally determining it was a blown fuse all along.
--Method one: using a multi meter I first set the meter on the lowest ohms setting and touch the lead ends together noting the ohms reading (OR). Next I remove the glow plug wires from all three plugs and then attach the positive probe of the multimeter to the glow plug where the wire was. Then using a good ground (such as the negative on the battery terminal) I attach the ground probe of the multimeter to it.
With the ground wire on the ground battery terminal I touch the glow plug positive connection for a reading of 2.3 ohms. Subtract your calibration number of 1.3 which gives you the glow plug draw of 0.7 ohms.
I record this reading and subtract the OR reading from it which determines the ohms draw on that particular glow plug. I then check the manual for acceptable specifications. If it falls within acceptable allowances I then move on to the next and so on until the glow plug that does not read properly is found.
--Method two: To isolate the faulty glow plug I first cycle through the pre heat sequence and then
My thermometer has a laser beam that directs to the exact place it reads from; that round red cap is covering the air intake to prevent any debris from entering during the repair
using a laser hand held thermometer take a reading of each one. These little thermometers are real handy, cheap to buy and a welcome addition to the tool box. The premise of glow plugs is to heat up, generating heat in the combustion chamber assisting in the successful burn of the injected fuel. So when they are working properly they get hot. This will be picked up by the thermometer.
--Method three: is to again cycle through the pre heat sequence and then quickly touch each glow plug by hand; the one that’s cold is the looser. Quickly is the key word here because they do get hot. This method, although somewhat crude, is a reliable choice as it’s fast and easy to do, remembering of course “quickly”. On the down side the second and third choices do not provide information that would determine the condition of all of the glow plugs which is the proper way to do this job allowing a thorough check of the components while you are under the hood. All the glow plugs that are not within the specs should be replaced.
I drove to the North Shore Kubota/John Deer dealer east of Sault Ste Marie and met with
I took with me my old glow plug and mechanic Joseph Boulanger checked it with his meter, coming up with the same reading of 0.7 ohms. Acceptable limits are 0.3-0.5 ohms, meaning that this one is on its way out
mechanic Joseph Boulanger to get a comparison between old and new, orange and green. Joseph showed me a new Kubota BX23S and a new John Deer 1025R of similar displacement. Surprisingly, the Kubota engines glow plugs are almost the same in the new tractor as my old engine except the price:
--KUBOTA B7200 NGK # Y-103V $23.60
--KUBOTA BX23S NGK # YE01 $69.44
--JD 1025R p/n MIU802457 $52.09
Replacement:
Changing off my old glow plug was not a huge issue and goes like this: as the wire is already off from doing the check I used a pick to scrape around the perimeter of the glow plug and then using my shop vacuum removed any built up grit as when removed you expose a void that could allow foreign material to enter. Using a wrench the glow plug was removed and replaced with the new one. Torque to manufacturer specs, attach the wires and that’s it; we’re done.
I mentioned the glowing plug that my B7200 has on the dashboard. Just ahead of the dashboard on the hood is the fuel filler cap. While filling with fuel I had a fight with a siphon tube this winter and the dash got a dousing of diesel. Wiping it off with a cloth buffed the pretty orange up but didn’t remove it from the glowing plug. For several start sequences to follow, I could smell burning diesel. Always exercise caution.
— Dan Kerr