12 volts between the positive terminal of battery and glow plugs at all times, bad?

[Soundguy]

I just connected my multimeter to the positive battery terminal and positive connection on the glow plug and my meter read -13.49V (see picture at address below).

http://img.photobucket.com/albums/v347/kawiracer/Tractorvoltagereading_zpsce2ff547.jpg

When I place my negative lead on the negative terminal of the battery and the positive terminal on the positive connection for the glow plug, I get no voltage until I turn the key to the "heat glow plugs" position, and then I get a reading of only 10.96 to 11 volts. Perhapps that isn't enough to warm the plugs? Would that make more sense? I know that the engine is a little tired (about 1100 hours), but I'm hoping I'm not fighting an engine with low compression.

Thanks everyone!

it's exactly what I expect to see. that glow plug is a very low ohm, high current laod.

if you say battery volts there with key on.. i'd say the plug was OPEN.. but that voltage drop is entirely normal.. resistors have a voltage drop across them.. that glow plug is a resistor. ( heating element ).

 

[RickB]

Your conclusion that all causes except low compression have been eliminated is incorrect. Take a step back and be CERTAIN that you have an adequate supply of fuel at the injection pump. Make sure you have a decent battey, cables and starter so your cranking speed is sufficient to start the tractor. All else fails, tow it in high gear and see if it will start & run. Tearing into the engine based on current info is probably a mistake.

 

[aczlan]

Are you sure about those pressures? I always thought a diesel engine should be in the 350-400 psi range (gas engines usually go about 125-150 psi). The 700 psi reading would indicate a CR of roughly 50 to 1.

Thats what his numbers were and he is the only place I would go if rebuilding a D24. I think the Volvo spec is 313 to 455 psi, IIRC the D24T he rebuilt for Dad was at least 600PSI on all 6 cylinders.

Aaron Z

 

[Hooked_on_HP]

Have you tried fresh fuel. With todays bio fuel it can go bad in a hurry .
I would put in fresh fuel and rebleed the system. Do you have a service manual and are you bleeding it properly.
Bill

 

[SilverLakeFab]

Thanks to everyone for chiming in on this one. The battery is new and the motor turns at a sufficient speed to start (or at least that was all it took when the tractor ran). The fuel should be just fine as the tractor is stored indoors and it had a fresh tank of fuel when it ran last. My handy compression tester arrived today and I took readings from all three cylinders. The front cylinder measured in at 260 PSI, the middle measured in at 208, and the rear measured in at 300 PSI. I think it's safe to assume that it's time to rebuild something, and by the time I tear that motor down to do a full inspection, it would make sense to put a whole new rebuild kit in it (pistons, rings, bearings, seals, gaskets), as I don't want to have to tear it down again because I neglected to change something out. All that said, I received a quote for a full rebuild kit last week from Country Sales and Service. The bill comes in at $679.19 (standard or 0.5 mm oversize). Honestly, that's not a bad deal to get absolutely everything needed to rebuild that little motor. I figure if I have to get it bored, that will run me about $350 at the local machine shop, so I'll be out of it for just over $1,000. That's a chunk of change to put into a 700 cc engine from 1978, but I can't buy a new tractor engine for that, so it's worth it.

On a side note, the diesel compression tester I purchased from Harbor freight was of impressive quality, especially for the whopping $40 I paid for it. If anyone needs one of those for non-professional use, I don't see a better deal.

 

[Soundguy]

i didn't see wet numbers and dry numbers.

 

[SilverLakeFab]

Those numbers are without the injectors connected to the cylinders because the fuel lines are right in the way to be able to connect the compression tester. The pressure numbers are different enough cylinder to cylinder for me to assume that I either have a piston compression problem or a cylinder valve leak problem. I plan to purchase a service manual before tearing anything down to make sure I don't mess anything up. I'll post details for what I do to test or repair further. I'd love to do a full rebuild, but I first need to save some pennies.

 

[aczlan]

Before you tear it down, run a wet compression test. See Technical Articles at Greg's Engine & Machine for directions. That will tell you if the problem is rings or valves.

Aaron Z

 

[crazyal]

Before you tear it down, run a wet compression test. See Technical Articles at Greg's Engine & Machine for directions. That will tell you if the problem is rings or valves.

Aaron Z

If the engine ran couldn't the addition of oil into the cylinders cause the engine to fire up?

 

[brain55]

If the engine ran couldn't the addition of oil into the cylinders cause the engine to fire up?

Yes, if it had sufficient compression. Not likely with those numbers. If they were in the 400+ psi range there is a good chance it would, but only for a few revolutions, not a big deal.

Brian