Is this Kubota d722 blown?

[Hyakkimaru16]

My name is Tristan and this will be my first thread on this site but, I'm excited to meet everybody. I have a Lincoln ranger 305d generator welder with a Kubota d722 3 cylinder diesel engine on it. I got it in a trade and I got other stuff as well but, I would like to get this thing working so it can be my new mobile welder rig. Well this particular engine comes with up to a 3,000 hour major engine parts warranty and I am barely over half of that. About 1800 hours. First thing I did was bleed all the air out of the fuel system and out of the injection system trying to crank it. Well after messing with it for quite a while and having no luck even spraying diesel directly into the intake, I did a compression test. Cylinder one, I assume it's cylinder one. It's on the flywheel side. 120 psi, cylinder 2 240 PSI, cylinder 3 350 PSI. Obviously there's problems. So I pull the motor and remove the head. The valves are rusted pretty good, and likely pitted although I have not removed them yet. The cylinders look like crap but I can't feel anything with my fingers. Everything feels smooth to the touch although it doesn't look great. A little while ago I was recommended to try some transmission fluid in the cylinders and turn it over with the starter for a bit to clean up some of the build up and see where I stand so, after doing that for about 10 minutes intermittently, this is what was left. Doesn't look great. The black spots at the top of the cylinders I can feel with my fingernail. I don't know if it's crud buildup or if it's a burn spot or what. I don't know if somebody ran gas through this thing, there's no telling. Again, the valves look terrible so I'm kind of tempted to rebuild the head and slap a head gasket on it and retest compression but, what do y'all think? I did make a short video showing off the cylinders and head before I did all of the stuff I've currently done and I will post a link to that as well. Let me know if you think I should just have the cylinders honed and put oversized Pistons or if I could get away with new standard pistons and rings and a light touch up hone or what. Let me know, thanks.

Everything but the first picture are from before turning it over with transmission fluid. The first picture is the after.

 

[ROUSTABOUT]

You could very easily have a broken ring. You can have a broken land. That is the raised part of piston between the rings. I have put kubotas together that looked way way worse than yours. Been running fine over ten years now. You can remove the valves and grind them yourself. You can pull the rods and Pistons to re ring it. I've rebuilt many engines. Never bored one. Don't turn the bottom of injection lines at the pump. You have to be very careful about that. If you turn that boss in the pump that the injection line screws to, there goes your timing. You'll have to send the pump off to get timing set, so don't turn it. Battery drills on slow are magical honing devices. Just hone it lightly. I use double Dee farty (WD-40) and clean white paper towels to clean cylinder after honing. Keep wiping cylinder out until you get a clean paper towel. Check your head for flatness while it's off. Don't fool with the crank. Just take rods and Pistons out. Keep them numbered and turned the right way. You can get some rod bearings if they show much wear.

 

[Hyakkimaru16]

You could very easily have a broken ring. You can have a broken land. That is the raised part of piston between the rings. I have put kubotas together that looked way way worse than yours. Been running fine over ten years now. You can remove the valves and grind them yourself. You can pull the rods and Pistons to re ring it. I've rebuilt many engines. Never bored one. Don't turn the bottom of injection lines at the pump. You have to be very careful about that. If you turn that boss in the pump that the injection line screws to, there goes your timing. You'll have to send the pump off to get timing set, so don't turn it. Battery drills on slow are magical honing devices. Just hone it lightly. I use double Dee farty (WD-40) and clean white paper towels to clean cylinder after honing. Keep wiping cylinder out until you get a clean paper towel. Check your head for flatness while it's off. Don't fool with the crank. Just take rods and Pistons out. Keep them numbered and turned the right way. You can get some rod bearings if they show much wear.

Thanks so much for the reply. I was thinking since the valves were so bad that maybe that was the cause of low compression. I figured after doing a valve job maybe I should slap a head gasket on it and retest compression before I buy new pistons and rings. What do you think?

I Lapped the valves yesterday but, this is my first time so, does this look acceptable? Also here are some before and after pics so you can see how bad they were. A lot of rust.

 

[ROUSTABOUT]

Valves look fine. Always lap them just enough to clean them up, and no more. I would get them Pistons out and replace the rings, hone it lightly, don't try to clean the cylinders up. Just hone it lightly. You don't know how bad it was before you got it. I just wouldn't get in it as far as you have without doing rings.

 

[mrmikey]

What he says. You're into it 3/4 of the way anyway, why not hone the cylinders to get a light crosshatch and check the rings anyway.

 

[Hyakkimaru16]

I do have a reason for not wanting to put to much time into rebuilding the engine if I don't have to. The generator may be bad, the welder may not work, then I would have money and time in a basket case and have to try to sell the engine. Also, this is my first engine rebuild. I don't have any of the tools. No hone, no torque wrenchs. I buying the tools I need for this as I go. I do a lot of diesel work on the side but have never messed with engine internals. Mostly just diagnostics and repair.

However, that being said I do feel like I should go ahead and pull the Pistons and buy a cylinder hone and some rings. Worst case if the welder is junk I will have a good engine for something or to sell.

Thanks for the advice y'all, I will get that done and retest compression and hopefully have a running motor!

 

[Mike1955]

And the Ginny will most likely work. If it doesn’t let us know. I can walk you through a lot of it

 

[Hyakkimaru16]

Awesome, I'm excited. Since this is my first engine, I don't know a whole lot about honing and what not. I've heard for this application a ball hone or, also known as a flex hone would be the best for just deglazing. What grit should I get though? Brand? Is a $50 ball hone from Amazon going to do any good? What type of material ball hone should I get? Should I buy or build an engine stand or can I get by without one? Only OEM pistons and rings? Or replace the rings and reuse the Pistons? I guess I'll figure that part out when I actually get them out.

 

[jjeff]

Get a torque wrench in my experiences even a cheaper beam type 3/8 and 1/2" drive. Good luck.

 

[ROUSTABOUT]

Awesome, I'm excited. Since this is my first engine, I don't know a whole lot about honing and what not. I've heard for this application a ball hone or, also known as a flex hone would be the best for just deglazing. What grit should I get though? Brand? Is a $50 ball hone from Amazon going to do any good? What type of material ball hone should I get? Should I buy or build an engine stand or can I get by without one? Only OEM pistons and rings? Or replace the rings and reuse the Pistons? I guess I'll figure that part out when I actually get them out.

I always use the three blade hone. Ball hone will work. I've wrapped a home with sand paper and trucked along just fine. That little engine, you just need a table. Use the same Pistons if they look fine. No welder is junk. You have to have a good running engine to get the welder right. It's all fixable. YOU CAN DO IT. Just mark them rods and rod caps with a punch. Right near where the cap joins the rod. One mark on rod and one mark on #1 cap. Two on #2, three on #3.