I did the fountain test with the injectors and glow plugs in. I could do the test again with them removed but as it does not stumble under a load I think I will just run it as long as I will need it for the summer and fall. If the low compression and smoking on startup are still occurring I will tear it down this winter, get the front cover off and check the timing marks. That will give me a baseline for moving forward. Thank you for your help. Larry.
B7100 Piston Installation
- Thread starter Schmotown
- Start date
Hi Larry,
as far as I understand is the smoke at startup the problem, after that the tractor is running fine and has power.
The smoke is either oil or Diesel that got into the exhaust unburnt. You mentioned poor starting. This is what I would focus on. The glow plugs you changed already but I would ask you to measure the current into each of them when pre glowing. I had a faulty glow plug and this lead to the same symptoms what you are seeing, a lot of smoke at startup and then running fine. Low compression could be the cause of that too of course.
Wrt to the injection pump, without the injectors no pressure is building up and all you see is a small drop of Diesel, which is basically all a cylinder gets per ignition.
Kind regards,
Hugo
as far as I understand is the smoke at startup the problem, after that the tractor is running fine and has power.
The smoke is either oil or Diesel that got into the exhaust unburnt. You mentioned poor starting. This is what I would focus on. The glow plugs you changed already but I would ask you to measure the current into each of them when pre glowing. I had a faulty glow plug and this lead to the same symptoms what you are seeing, a lot of smoke at startup and then running fine. Low compression could be the cause of that too of course.
Wrt to the injection pump, without the injectors no pressure is building up and all you see is a small drop of Diesel, which is basically all a cylinder gets per ignition.
Kind regards,
Hugo
torch
Well-known member
Equipment
B7100HSD, B2789, B2550, B4672, 48" cultivator, homemade FEL and Cab
torch
Well-known member
Equipment
B7100HSD, B2789, B2550, B4672, 48" cultivator, homemade FEL and Cab
Just for fun and giggles, I investigated my B7100 (1994 version) exhaust manifold temperatures with a TIC. I set it to °F for consistency with your readings and turned on high, low and centre spot readings. After about 20 minutes of running:
180°F at #1, 220°F at #3. 40°F difference. Ambient temp 75°F.
I don't think you have anything to worry about. Ok, it's sample size of two, but thus far 100% of all D750 engines investigated show notably lower EGT at the #1 cylinder. <lol>
Last edited:
North Idaho Wolfman
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L3450DT-GST, Woods FEL, B7100 HSD, FEL, 60" SB, 743 Bobcat with V2203, and more
The numbers your looking at are not right
They did not make an HST in 1976
@torch gave you the link for an B7100D
Your HST has to be 1980 or newer
TractorData.com Kubota B7100HST tractor information
Okay, looks like I have a 1983 tractor as my S/N is 12104. Thanks for the info!The numbers your looking at are not right
They did not make an HST in 1976
@torch gave you the link for an B7100D
Your HST has to be 1980 or newer
TractorData.com Kubota B7100HST tractor information
www.tractordata.com
torch
Well-known member
Equipment
B7100HSD, B2789, B2550, B4672, 48" cultivator, homemade FEL and Cab
Ooops. Sorry about that. I forgot they divvied up the B7100s that way. I was just thinking "older".The numbers your looking at are not right
They did not make an HST in 1976
@torch gave you the link for an B7100D
Your HST has to be 1980 or newer
TractorData.com Kubota B7100HST tractor information
North Idaho Wolfman
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L3450DT-GST, Woods FEL, B7100 HSD, FEL, 60" SB, 743 Bobcat with V2203, and more
Hugo,
The total amps for the glow plugs is 19A. I pulled all 3 glow plugs and powered them with jumper cables. They all glowed bright red and I think they're in great shape.
I have one more question (for today) about the low compression (300 psi) on all (3) cylinders of my rebuilt B7100:
I verified that cylinder #1 is at TDC of the compression stroke and did a leak down test again on that cylinder. At 100 psi inlet pressure my leak down gauge was reading about 8% loss. With the intake manifold removed I sprayed a soap solution through the #1 intake port and took a video (see below for link) of the bubbles coming from the back side of the valve while there was 100 psi in the cylinder. Does it make sense that there is this amount of leaking (bubbles) when there is only 8% leak down?
During this test I also taped a lightweight latex glove over the breather tube to check for blow-by and the glove did not inflate. Thanks for any comments. Larry.
I verified that cylinder #1 is at TDC of the compression stroke and did a leak down test again on that cylinder. At 100 psi inlet pressure my leak down gauge was reading about 8% loss. With the intake manifold removed I sprayed a soap solution through the #1 intake port and took a video (see below for link) of the bubbles coming from the back side of the valve while there was 100 psi in the cylinder. Does it make sense that there is this amount of leaking (bubbles) when there is only 8% leak down?
During this test I also taped a lightweight latex glove over the breather tube to check for blow-by and the glove did not inflate. Thanks for any comments. Larry.
torch
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Equipment
B7100HSD, B2789, B2550, B4672, 48" cultivator, homemade FEL and Cab
They won't be if you keep doing that! They are supposed to be in series with the indicator, which drops the voltage. They are not designed or intended to be subjected to full battery voltage. Connecting them directly will burn them out sooner or later -- probably sooner.
torch
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B7100HSD, B2789, B2550, B4672, 48" cultivator, homemade FEL and Cab
8% isn't unacceptable, especially for a recently rebuilt cold engine. I assume you zeroed the gauge before starting the test?
It is certainly leaking past that valve. It is possible that lapping the valve might reduce the leakage. But bear in mind that the bubbles you are seeing are the result of a constant steady pressure. When running even at idle -- say 500 rpm -- that cylinder sees compression for about 3 tenths of a second at a time, so the volume of leakage per stroke is considerably less. I think this is a case of things looking worse in a static situation than they really are when viewed dynamically.
Similarly, rolling the engine over by hand seats the valves very gently without the normal velocity. It is possible that the valve can do better than that. Try doing the test again with the rocker cover off. With the cylinder pressurized put a piece of wood on the valve stem side of the rocker arm and give that a rap with a hammer to pop the valve open slightly and reseat it under pressure. See if that affects your percentages.
What happened with your compression readings when you installed the special valve core?
It is certainly leaking past that valve. It is possible that lapping the valve might reduce the leakage. But bear in mind that the bubbles you are seeing are the result of a constant steady pressure. When running even at idle -- say 500 rpm -- that cylinder sees compression for about 3 tenths of a second at a time, so the volume of leakage per stroke is considerably less. I think this is a case of things looking worse in a static situation than they really are when viewed dynamically.
Similarly, rolling the engine over by hand seats the valves very gently without the normal velocity. It is possible that the valve can do better than that. Try doing the test again with the rocker cover off. With the cylinder pressurized put a piece of wood on the valve stem side of the rocker arm and give that a rap with a hammer to pop the valve open slightly and reseat it under pressure. See if that affects your percentages.
What happened with your compression readings when you installed the special valve core?
Russell King
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