b7500 Glow Plugs removal and testing

[drewzee87t]

Hi,

new to me b7500 w 1600 hours. Slow starting when cold. The GP light works when key is turned right. I have checked and with switch on GP's I am getting 10.3 to 10.5 volts. Has 3 GP's with a buss bar on the positive that connects all three. I cannot get to them well enough to remove the bus bar so I cannot pull them to do a proper test. W or even get to them individually with a meter. Withh all three connected to the bus bar I get .5 OHM reading and my leads zero out at .2 Ohm, so the three together are reading .3 ohm. I don't know the math for series resistance on these, so does that sound right?

I can't really tell but it seems the two I can touch the top of are not getting noticeably warm (or HOT) after holding the circuit on for up to a minute. So I really suspect they are toast and hopefully that's all that's wrong.

WSM for unit is coming next week. I have to remove the gas tank to even get to the GP's and I can't get to the bolts that hold the rear bonnet between the hood (removed) and the dashboard.

It won't start when cold very easily and by cold I mean 65F. I have run up the GP's to 30 seconds and feel that should be too long. It will start after about 20 seconds of cranking and a big puff of gray/black smoke. While cranking I do get unburned fuel mist. Once warm it fires up right away.

D1005 motor. Battery is in good shape, oil and filter changed. I haven't done anything to fuel system yet but seems to be okay. Needs a new air cleaner, but makes no difference if air cleaner removed when starting cold.

Does .3 ohm sound like a good reading for all 3 GPs on the bus bar, or do I have to take this whole thing apart to get to it? It's really not obvious at all how to get the metal sheet that covers the fuel tank off. I think I will need to pull the instrument cluster to get to it, but will wait till I have the actual manual so I don't ruin anything.

Is there a GP Controller or other stuff in there? All I can find is just the positive going to the GP bus bar. It would appear to be a manual GP switch where you need to count off the time for yourself.

Thanks for any info. I am kind of in prayer mode that I haven't bought a heap that needs a ring job. Rest of tractor seems well maintained, clean and no leaks. Everything works...

 

[1970cs]

You need to remove the buss bar and pull each glow plug and ohm each one individually! 7 ohms or less is a good reading. Check for swelling of heating end.

If the above does not reveal anything, you may want to run the valves and re-lash them and yet another maybe delivery valve washers in the injection pump.

You talked about a rebuild! Do you have a lot of blow by coming out the vent?

Pat

 

[Diydave]

Another way to test them is with an IR thermometer. Glow the plugs, and check the temp of each. If you have to take them out, it would be a good time to check compression, through the GP holes...

Oh, and welcome to the forum...

 

[drewzee87t]

Thanks. I don't have any way to get to the buggers without removing the shroud and I can't figure that out quite yet, so I guess I will get back to you all whenever I can get to them and pull them for a proper test. I don't think 7 ohms is a good measurement for any glow plug, but I will leave that alone until I get a proper test. There is blow by, it's an old tractor. Runs great once you get it going.

Patience is what I need unless someone can help me get the shroud/bonnet thingy off.

 

[1970cs]

Thanks. I don't have any way to get to the buggers without removing the shroud and I can't figure that out quite yet, so I guess I will get back to you all whenever I can get to them and pull them for a proper test. I don't think 7 ohms is a good measurement for any glow plug, but I will leave that alone until I get a proper test. There is blow by, it's an old tractor. Runs great once you get it going.

Patience is what I need unless someone can help me get the shroud/bonnet thingy off.

First off, I don't think I have run into a shroud over the glow plug area on any small diesel. The hood or bonnet if that what you are referring to? Twist the chrome knob on the front of the hood/bonnet or what Kubota calls the mascot.

Also here is the NGK testing procedure procedure for glow plugs:http://www.ngk.com.au/glow-plugs/technical-information/glow-plug-analysis. Which their value for ohms was very close to suggested test value that I gave you!

Also if you could have an open glow plug which read no value which is bad also.

Look I have worked for an agriculture dealership for 22 years. I started as a tech and worked on everything from lawn and garden tractors to combines. I have worked parts, and sales also. So I am no stranger to these products.

Pat

 

[chim]

....................... Withh all three connected to the bus bar I get .5 OHM reading and my leads zero out at .2 Ohm, so the three together are reading .3 ohm. I don't know the math for series resistance on these, so does that sound right? ......................

With a bus connecting to one end of each glow plug and the engine block grounding the other end, the GP's are in parallel. If each of the three has a cold resistance of 7 ohms, the reading with all 3 connected should be around 2.3 Ohms.

 

[mendonsy]

I suspect that "7 ohms" is off by a decimal point. It is more likely to be something like 0.7 ohms.
I have never had to fool with the glow plugs on my B7500 but I do know from bitter experience that the Bosch glow plugs in a Mercedes diesel are 0.71 ohms when new and anything less than 0.5 ohms is a bad one.

edit: Page 9-S9 of the WSM says that the B7500 glow plugs should be approximately 0.9 ohms.

 

[D2Cat]

What you call the bus, kubota call the "glow plug cord". It is held onto the glow plugs by a nut. Typically, that nut has a slot across one side. You can insert at flat-blade screwdriver into the slot to remove the nut. Then the connecting "bus" can be removed. You can then use your meter to test each glow plug.

If you eventually need to replace the GP I'm pretty sure you will need to remove the intake manifold to get the front GP removed. The intake manifold may be what you are referring to as a "shroud".

 

[drewzee87t]

Hi - What I will refer to as a shroud is the metal that connects to the dashboard/instrument panel. I have attached pictures. The gas tank and some firewall/protective plastic stuff is in the way of the second and third GP. I have pretty dainty hands and I have wrenched on a lot of Japanese imports, so I am not averse to tight spaces. I can barely get a finger to even touch the GP that's under all that. I need to remove the shroud. The bus bar I refer to is the metal bus bar that connects all three GP's. I will figure out how to get this apart then I will properly test them.

Pat, that's a mighty fine looking...um....tractor.

 

[1970cs]

Ah, fuel tank and cowl removal will make it more better to get to.

The seat cover is optional, a very high priced option!

Pat

 

[drewzee87t]

Updated

So I was able to get to the glow plugs. I ended up learning a whole lot about all the stuff between the steering wheel and the back of the engine, then just cut the insulation stuff out that was in my way and now I can get to what I needed.
I pulled the bussbar off the GP'S and it had some oil on it, not super tight but the bus was clean and shiny. I don't think any potential issues.

I was then able to test the GP's for resistance, all came in at 1.2 or 1.3 OHM with my leads zeroing at .2. So all at about 1 ohm. GOOD.

Well, not really. I was hoping the GP's were the problem with starting. I pulled them and bench tested for actual performance and they are all good on a battery, they are full glow within about 10 -12 seconds. So they are all good. Why is it hard to start?

The interesting thing is that they were all completely covered in oil when I pulled them out. Like little dipsticks covered in oil.

When I got this the oil was overfull at least a quart. I figured that and Gp's would be the reason for hard starts. I have changed oil/filter and run the machine for a couple hours in various RPM including actually doing some stuff before I decided to figure out the hard cold starts. I don't see any more oil than what I put in it yet. I have heard of hydrostat seal that will dump hydrolic fluid in the crankcase, and so far I don';t think that is at play.

Is it possible that the over oiled condition would cause the GP's not to be able to preheat since they seem to be sitting coated with and drowning in oil? If so, how would you recommend cleaning out the pre ignition or whatever it is called on the engine? I am thinking I might blow crank the engine with fuel cutoff engaged a bit and then run some carbie cleaner into the GP ports and let it sit for a while, then spin it up and hope it might clean out any gunk that might be blocking it up?

The other reality is that I don't have a diesel compression gauge and I do have blowby when it is running, more when at low rpm's and less at higher rpm';s .

Next steps? It will start the way it is and it runs fine. It's just hard to start and my monkey mind thought its just GPs and will be fine. Now I am worried that it's overall compression problem. I have heard of people running these things for 1000 hours or more after they started getting blow-by.

Ok, now Pat and others, hopefully that gives you more info's to work with. Thank you again for your help***8230;.

 

[1970cs]

I would believe that a compression test and cylinder leak down are needed at this point.

It's also possible that the mechanical fuel pump could be overfilling the crankcase with fuel? Creating an overfilled crankcase.

Pat

 

[drewzee87t]

I have not had any luck sourcing a compression tester. I did finally end up with finding one and it does not have the correct adaptor for the glow plugs. Any idea what the right size adaptor is and where one might be sourced? I am just going to put it back together for now. I can get to the GP's pretty easily now that I cleared out some room.

 

[Daren Todd]

I have not had any luck sourcing a compression tester. I did finally end up with finding one and it does not have the correct adaptor for the glow plugs. Any idea what the right size adaptor is and where one might be sourced? I am just going to put it back together for now. I can get to the GP's pretty easily now that I cleared out some room.

Harbour freight has a pressure test kit with the correct fitting.

 

[drewzee87t]

I got the HF one and it's for a bigger GP 10 *1.25 the one I need is 8 * 1.00. I had to order one from a tool supply (not HF). I can't do the test until that gets here in a few days or a week or whatever.

I put it back together, cleaned up all the contacts, checked that I am getting good volts at the wire that connects to the bus when switch is on heat. Good.

I tested with the GP's plugged back in and when key is on heat, the GP are only getting 9.5-10 volts and the engine will not start. I guess not enough current?

I hotwired the GP's direct off the battery and tested that with them in circuit I was getting full battery volts. At about a minute or so of heating (however much time it took me to read the voltage), I cranked and it fired up after only about 5-8 seconds on the starter.

I will re-do the test again tomorrow if I get a chance, but it seems there is not enough current capacity in the stock GP wire. I may go mad-max and rig up a spare relay to switch it to power direct off the battery using the existing GP wire just to close the relay. It's probably the ignition switch at fault.

I still need to do the comp test and will get back with results of that and my continued adventures in GP circuit. At this point I have good GP's and have verified that I have a problem with my GP circuit that seems to be at least part of the hard start issue from not letting the GPs properly heat up.

 

[D2Cat]

The power comes through the key switch to the glow plug indicator to the GP. Maybe your battery isn't up to par.

 

[drewzee87t]

Battery is fresh and test was done with battery hooked up to an external "extra" battery. Based on your input, I think the switch itself is not flowing the required current. I will see if I can clean up the contacts since I already have the cluster pulled out and can get to it. Will post back tomorrow if I get to it. Thanks all for your helps!

 

[D2Cat]

Maybe the glow plug indicator has too much resistance and causing the low voltage at the GP.

I think for a test you could put a jumper wire on the switch and then to the back GP where the bus is connected (by the firewall). Hold for a count of 10-15 seconds and see if it fires up.

If it starts quickly, then you need the GP indicator.

 

[drewzee87t]

This doesn't have a "cigarette lighter" GP indicator like the older tractors. There is an actual light in the instrument cluster that turns on when the GP circuit is active. If there is resistance it is coming from the key switch itself or other parts of the circuit. Is the GP indicator a dropping resistor in the older tractors? My test yesterday pretty much confirmed that it starts up if you get enough juice to the GP's, but I don't want to over-volt them and burn them out if they are not supposed to get 12 volts...thanks

 

[mendonsy]

Page 9-S20 of the WSM says the glow plug voltage should measure approximately the same as the battery voltage. I don't think there is any chance of damaging them. You must have a bad connection somewhere.