JD 855 Won't Start

[Dennisfly]

The engine is a Yanmar 3TN75RJ 3 cylinder 24 HP. The tractor has always started hard in the cold. I bought it used and have had it for 7 years. It has a replacement tach, so I don't know total hours, but it appears to have been used quite a bit. I installed a block heater and could always start in the cold if pre-heated. Once started, it always ran well, had good power, no smoke, used no oil, and has no unusual noises. The last time I ran it, it ran well, but now will not start. I preheated it until it was warm to the touch, so it is not a cold problem. I bypassed the air filter, so it isn't an air problem. I replaced the fuel filter, used new fuel, and pulled two injectors, hooked them up out of the head, and watched them spray, so I know it isn't fuel. It must be compression.


I bought a compression guage and adapter, made a custom hold down bracket and did a compression check (1/2 check actually). The manual calls for minimum compression to be 384 PSI with no more than 71 PSI difference between cylinders. The check should be done with the engine warm, which is impossible because it won't start. My plan was to check each cylinder dry, and then squirt several shots of oil into the cylinder , turn it over and test it wet. Improvement in the wet test indicates bad rings.

The number one cylinder tested 250 dry and 320 wet.
The number two cylinder tested 220 dry and then the tester relief valve broke and that was the end of the testing for now. Testing will continue when the defective relief valve is replaced.

Based on what I've seen so far, it indicates bad rings.

I hope to remove the head and have the valves ground, and any other work required, by a machine shop.

If the taper is not too bad in the cylinders, I hope to remove any ridge, hone the cylinders, replace the rings, and put the whole thing back together. If it's bad, boring and new pistons may be necessary. I will check rod and main bearing clearances with Plasti-gauge and hope they are good. Since it doesn't knock, burn oil, or make other strange noises, I'm hoping I don't need a complete overhaul/remanufacture, but that is a possibility and I'll do it if necessary.

Comments please. Is my trouble shooting and diagnosis correct

 

[zzvyb6]

Have you tested the glow plugs to see if they are still heating? I have a similar motor in a lawn mower. All 3 glow plugs were dead. Now it starts easily in 15 degree weather. If you can put a few drops of heavy weight oil in the cylinders, it may seal the rings enough to get some compression. Then it may start.

 

[2manyrocks]

I had a F250 diesel that would not start without the glow plugs working. Since you have fuel spraying from the injectors, that's where I'd start. If air has gotten in the fuel system, it can be a pain to get it purged.

 

[Egon]

This engine may not have glow plugs but an inlet air heater instead.

 

[Jerry/MT]

The engine is a Yanmar 3TN75RJ 3 cylinder 24 HP. The tractor has always started hard in the cold. I bought it used and have had it for 7 years. It has a replacement tach, so I don't know total hours, but it appears to have been used quite a bit. I installed a block heater and could always start in the cold if pre-heated. Once started, it always ran well, had good power, no smoke, used no oil, and has no unusual noises. The last time I ran it, it ran well, but now will not start. I preheated it until it was warm to the touch, so it is not a cold problem. I bypassed the air filter, so it isn't an air problem. I replaced the fuel filter, used new fuel, and pulled two injectors, hooked them up out of the head, and watched them spray, so I know it isn't fuel. It must be compression.


I bought a compression guage and adapter, made a custom hold down bracket and did a compression check (1/2 check actually). The manual calls for minimum compression to be 384 PSI with no more than 71 PSI difference between cylinders. The check should be done with the engine warm, which is impossible because it won't start. My plan was to check each cylinder dry, and then squirt several shots of oil into the cylinder , turn it over and test it wet. Improvement in the wet test indicates bad rings.

The number one cylinder tested 250 dry and 320 wet.
The number two cylinder tested 220 dry and then the tester relief valve broke and that was the end of the testing for now. Testing will continue when the defective relief valve is replaced.

Based on what I've seen so far, it indicates bad rings.

I hope to remove the head and have the valves ground, and any other work required, by a machine shop.

If the taper is not too bad in the cylinders, I hope to remove any ridge, hone the cylinders, replace the rings, and put the whole thing back together. If it's bad, boring and new pistons may be necessary. I will check rod and main bearing clearances with Plasti-gauge and hope they are good. Since it doesn't knock, burn oil, or make other strange noises, I'm hoping I don't need a complete overhaul/remanufacture, but that is a possibility and I'll do it if necessary.

Comments please. Is my trouble shooting and diagnosis correct

Your methodology is somewhat correct but I think you are jumping to a conclusion without systematically eliminating the fuel system and the starting aids as the problem. Using a block heater on a diesel with precombustion chambers doesn't eliminate the glow plugs as a culprit. These engines are hard to start without glow plugs.

After you replaced the filter, did you bleed the fuel system? Are you getting adequate fuel from the tank? Often the tank gets crud at the bottom that clogs the out let screen or the valve. If the temperatures have been below freezing icing in the fuel system can be the problem .
Did you validate power tothe glow plugs in the installed position? Did you power them up after removing them to see if they were glowing?

Since you could not get the engine to operating temperature, I doubt the level of the compression pressures is correct and you didn't exhibit any of the signs of a worn engine prior to this problem. You don't get a worn engine overnight.

Before you tear the engine down, make sure that the fuel system and the starting aids are working correctly before you go blaming other problems. Most problems with diesel starting are fuel related and those diesels that use glow plugs often have problems with the glow plugs or their power supply system.

 

[Wyobuckaroo]

I also have a JD855 (1987)
According to the parts look up online, it has an air intake heater.
There seems to be two different ones, early and late model.

Never had a failure to start. Always preheated with the block heater, and air preheat. Even down to -20 below.

Do you have fuel in your crank case oil ?
Keep us updated.
Good luck
Wyo

 

[David-Davies]

Hello dennisfly. Some times When a diesel won't start when it's cold out side, it is a battery- starter problem. Over the years the starter spins sower and slower, due to the battery getting old, and or the starter is getting old, or both. A starter is hard to test. As you test it it works better, as it heats up. Do you have the specks for your tractor??? Or you can call the dealer. Your engine must turn over at a given RPM to start. What might seem good to your ears nay not be fast enughf, especially, when it is cold out side. If you know some one that has a diesel engine, see if you can lisen to it turn over, and count how fast it spins. JD shoud have the specks
Dave

 

[Dennisfly]

Thanks everyone for the input.

The engine does not have glow plugs, it has an air heater. I have confirmed operation by removing the inlet elbow above it and watching it glow red. I also tried a start with a heat gun pointed down the inlet plus the block pre-heated.

I figured it was the fuel system too, but I've checked it extensively. The fuel is new. I looked in the tank and there is no sediment. I replaced the pickup screen in the tank. I replaced the fuel filter. There was no sediment in the fuel filter bowl and the filter was clean. I bled it at least four times from three different points. The inlet to the filter, the outlet from the filter and at the injector B nuts. Solid fuel and no air bubbles. The mechanical transfer pump is feeding the high pressure pump and the high pressure pump is opening the injectors (which requires 2800 psi). Hooking the injectors to the fuel lines with them out of the head and watching them spray confirms this.

I have charged the battery before each start attempt and the starter turnes it over at a good rate. I received a value of 200 RPMs to start. I think I'm getting at least that, but will watch the tach next time I turn it over.

There is no fuel in the oil and no coolant in the oil or oil in the coolant.

My concern is that even though the engine was cold when I checked compression, 250 and 220 are far below the 384 that it should be and I should have seen more. The increase from 250 to 320 after squirting oil in the number one cylinder, to me, would indicate worn rings.

Does anyone have any experience with the relative values of warm verses cold compression values? How about the increase from 250 to 320? It seems significant to me.

I intend to complete the compression check as soon as the new gauge relief valve arrives.

 

[Dennisfly]

I replaced the defective relief valve on the compression gauge and tested the second cylinder wet. I've not yet been able to remove the third cylinder injector, so can't test its compression, but I would guess it is similar to the first two.

So, the book calls for 384 PSI with no more than 71 PSI (where did they get the 1?)difference between the cylinders with the engine warm.

My test results, with the engine cold because it won't start:
Cylinder one Dry 250 PSI Wet 320 PSI
Cylinder two Dry 220 PSI Wet 280 PSI

The wet testing was after squirting some oil in each cylinder and turning it over.

My analysis is bad rings due to the increase in PSI for the wet testing and the initial low values.

Anyone want to comment, agree, or disagree befor I pull it apart?

 

[YesDeere]

I know your not supposed to do this but, hit it with a little ether. If you can get it to go then you can rule out everything else. Only use a little bit. When starting turn the key to crank right away so the heater doesn't have a chance to get hot. Once it is cranking then spray. Done this many times on older trucks and reefer units that had low compression.

Got a little pup trailer through thanksgiving time this way. Would not start on it's own. Gas it and go. Although it did have over 20,000 hours