Technical rebuild assist with D950

[fastline]

Dealing with issues with this engine in a piece of equipment. Others gave up on it so I took over. I am not a rookie with engines but never built a Kubota. I just went through the head after someone else paid to have it "rebuilt". I could valve springs that were not down in their homes, and at least 3 valves that were not sealing. That has been resolved but it appears the engine probably sat for many years and rust had formed on the bored which was honed, but left erosion in the bores. When attempting to start on a test stand, multiple attempts were made with 5-45sec of glow time. All resulted in nothing but smoke and only one cylinder even acted liked it wanted to go.

I detected plenty of blowby from the valve cover even without starting. Next step is obviously run a compression test, but I am sure it will fail and the blowby is likely enough for me to go in.

The liners seem very thin even though I can find +.50mm pistons. Not sure if that will yield a good result? Do they make +.25mm pistons? The liners do not look like much fun and seems like it will need bored to size anyway due to that fact?

 

[85Hokie]

the compression test will tell a lot about this engine- let us know what you find out

 

[Daferris]

This is not for the 905 but it still might be of help... https://media.toro.com/servicemanuals/Kubota05-E3B.pdf

 

[GreensvilleJay]

hmm, do they sell 'kits' of piston,rings and sleeves ?
I know they do for others ,including my forklift..but to do that, I'd have to know whether it has 3 rings or 4 rings.......sigh.It has massive 'blowby' that I recycle back into the air intake..keeps the garage floor cleaner !

 

[North Idaho Wolfman]

Done quite a few of these.
Yes if you sleeve it you'll need to have it bored to size.
I don't recommend over boring old sleeves as they almost always fail.

 

[TheOldHokie]

Done quite a few of these.
Yes if you sleeve it you'll need to have it bored to size.
I don't recommend over boring old sleeves as they almost always fail.

Whats the wall thickness on the liners?

Dan

 

[fastline]

Done quite a few of these.
Yes if you sleeve it you'll need to have it bored to size.
I don't recommend over boring old sleeves as they almost always fail.

What was the failure mode? Are the sleeves fully supported at the bottom or hang free? When building race engines, I used to have issue getting people to tear down and do pistons. Excessive piston slap could cause some unneeded drama.

I am not really for boring, but i'd probably consider +.25mm pistons. Apparently those are not made. I don't see how I would fly the bores as is but sometimes decisions need made. I am really hoping to find sloppy pistons and ring end gaps you could pass a football through, signaling that pistons/rings, and a good hone would probably get most of the blowby under control.

I don't expect to put many hours on this engine, and it is my own, so I am willing to wiggle a bit.

I did manage to burn out two glow plugs. We had the test battery on a charger so the glows were getting north of 14V and I suspect they did not like that much. They say 10.5V on them. They were pulling about 10A each. I was just trying to get a little more cranking speed. Because I didn't know how these engines normally start, I did not attempt to leave glows hot while cranking. Obviously that would help but at some point, it should have given more signs of health.

 

[North Idaho Wolfman]

Whats the wall thickness on the liners?

Dan

I don't have one that's out of an engine right now. but the best guess around .020 of an inch or .50mm

 

[North Idaho Wolfman]

What was the failure mode? Are the sleeves fully supported at the bottom or hang free? When building race engines, I used to have issue getting people to tear down and do pistons. Excessive piston slap could cause some unneeded drama.

I am not really for boring, but i'd probably consider +.25mm pistons. Apparently those are not made. I don't see how I would fly the bores as is but sometimes decisions need made. I am really hoping to find sloppy pistons and ring end gaps you could pass a football through, signaling that pistons/rings, and a good hone would probably get most of the blowby under control.

No the sleeves do not extend past the bottom of the block.
.25mm pistons would make you bore about 1/4 of the thickness out of the already thin sleeves.

 

[fastline]

Just my take after being in the engine. The liners are to provide a harder, more durable bore than cast iron can provide. Offering .5mm pistons seems pretty stupid IMO, and not a wise play. the bores are hard, and trying to run a boring setup in those bores is asking for problems. And honing would heat the hell out of the liners and cause irregularities.

Since i cannot find a single spec for a new liner ID, we are going to try to avoid that step. It would be ridiculous to have to hone 10 thou out of new liners.

 

[North Idaho Wolfman]

Just my take after being in the engine. The liners are to provide a harder, more durable bore than cast iron can provide. Offering .5mm pistons seems pretty stupid IMO, and not a wise play. the bores are hard, and trying to run a boring setup in those bores is asking for problems. And honing would heat the hell out of the liners and cause irregularities.

Since i cannot find a single spec for a new liner ID, we are going to try to avoid that step. It would be ridiculous to have to hone 10 thou out of new liners.

New liners for these require you to bore them after install.
It's too much to hone down.

 

[GeoHorn]

Honing while flowing safety-solvent as a good way to wash-away particles while keeping the process cool. No heating problem.