M6800 - 1500 hrs. Loud engine noise while brush hog running.

[Gus1957]

6' Woods brush hog mowing a hay field not cut yet this year to get weeds down. Set to leave stubble 6" high. Tractor had been running 3 hours with no issues. Constant RPMs with no bogging. Running in low range 2nd / 3rd gear. Stopped to go get more diesel fuel. Cooled down about 1 hour. Only about 75F out any how.
Came back and blew out radiator from weed seeds while adding diesel.
Continued to mow for another 2.5 hours when a loud noise shut engine down slowly. I turned off PTO lever quickly.

Neighbor pulled me out of the field about an hour afterwards as it started to rain. We tried to start tractor and it turns over and runs - sounds to be on 3 cylinders ?

Thinking a compression test and borescope are required.

Thoughts on causes and how to proceed?

TIA !

 

[JasonW]

Checked oil and coolant levels?
Any holes in the side of the engine block?
Did you hit anything with the bush hog?

 

[Gus1957]

Checked oil and coolant levels?
Any holes in the side of the engine block?
Did you hit anything with the bush hog?

No holes in block or leaking out oil. Coolant was good.

Didn't hit anything.

 

[JasonW]

I’m not sure if I would run it if it sounds like it’s missing a cylinder without an inspection camera.
But an easy way to tell is crank it up and check the temperature of the exhaust manifold with a temperature gun, if one isn’t hot that cylinder isn’t firing.

If you had a hole in a piston, it would have massive blow by, if you check for that also.

 

[North Idaho Wolfman]

Start it and immediately feel exhaust for dead cylinder.
Pull oil fill cap and check for excessive blowby.
Pull radiator cap and look for blowby or bubbles.
If it's got a dead cylinder, could be no fuel delivery or damage.
Compression test will do good.
Wouldn't bother with bore scope as most of these engines have a pre chamber and can't see past it.

 

[Gus1957]

Start it and immediately feel exhaust for dead cylinder.
Pull oil fill cap and check for excessive blowby.
Pull radiator cap and look for blowby or bubbles.
If it's got a dead cylinder, could be no fuel delivery or damage.
Compression test will do good.
Wouldn't bother with bore scope as most of these engines have a pre chamber and can't see past it.

Pulled oil fill cap and does have excessive blowby
Opened radiator cap and no bubbles

Engine runs smoothly with no noise-knocking. Starts right up.
Prior to this event tractor engine didn't knock or have white smoke.

 

[North Idaho Wolfman]

Pulled oil fill cap and does have excessive blowby
Opened radiator cap and no bubbles

Engine runs smoothly with no noise-knocking. Starts right up.
Prior to this event tractor engine didn't knock or have white smoke.

So it has white smoke now?

Go to the Injector lines and while running crack each line and listen for a drop in RPM's.

 

[JasonW]

Pulled oil fill cap and does have excessive blowby
Opened radiator cap and no bubbles

Engine runs smoothly with no noise-knocking. Starts right up.
Prior to this event tractor engine didn't knock or have white smoke.

Engine runs smooth now with no knocking? Before you said it seemed to be running on 3 cylinders.

 

[Gus1957]

Engine runs smooth now with no knocking? Before you said it seemed to be running on 3 cylinders.

It never had a knock.

I usually don't wear ear muffs operating this tractor, but the monotonous drone of mowing for hours is annoying. And at 69 my hearing is already fading. Wish I didn't have them on when this happened to get a better sense of incident.

It never had white smoke and still doesn't.

It still seems to be running on 3 cylinders, but very smooth.

I moved it about 50' in high range 1st gear with no hesitation closer to the barn.

Waiting for a mechanic friend who wants to take a look at it.

Trying to share information for learning purposes and that it may help others who are interested or experience similar problems.

Gathering more information on this as well as trying to find another tractor to finish the mowing and do field plowing shortly.

A local Kubota mechanic said if there is catastrophic failure in the cylinder it's not worth fixing. Haven't been able to find a dismantled M6800 with an engine. Messicks can get new engines for $13,750 + shipping - which I wouldn't go that route.

 

[JasonW]

Well running smooth and running on 3 cylinders(out of 4) must have different meanings to different people.

Did you ever check the exhaust with a temp gun? Or crack each fuel line separately to find the miss?

You said it has excessive blow by? Did it have blow by before the incident?

 

[JasonW]

I usually don't wear ear muffs operating this tractor, but the monotonous drone of mowing for hours is annoying. And at 69 my hearing is already fading. Wish I didn't have them on when this happened to get a better sense of incident.

I wear earplugs almost every day. And 100 percent every day while I’m at work, usually 6-8 hours at a time sometimes longer. You can still hear everything going on with earplugs. You wouldn’t have gotten a better sense of what happened without them.
Wear ear plugs. Once you loose your hearing it doesn’t come back.