Engine issues

[prh77]

M 25 engine.....D 850 Kubota ?... started to blow a lot of grey smoke. Compr. test revealed 0 PSI on back cylinder with 425 on 2 front. Rear cylinder valve adjustment tight, adj valves, compr came up to 90 or so. Removed head. Found back cyl piston to be pock marked, looks like small craters on the moon, head also has some pock marks. Its almost looks like a piece of hardware went through this cylinder, but I am not sure. Also, when removing injectors, back one was only hand tight while others took a breaker bar to get loose. Back injector tip is also very sooty and oily, while front 2 are uniform dark carbon layer. Couple of questions; could a loose injector and tight valves cause some type of mis-fire/detonation that could cause this internal damage? And are real Kubota parts still around for this engine. At the least I need a new piston and some head work. Cylinder bore looks good with no ridge. In the Tech WIKI there is an old article about a guy in the Bay area doing a partial rebuild. The pictures of his rear piston looks a lot like mine. Appreciate any help.

[Stu Jackson]

https://www.tractorpartsasap.com/salvage-equipment/kubota-salvage.html

or a Kubota dealer

Yes, it is a D850.

[KWKloeber]

Couple of questions; could a loose injector and tight valves cause some type of mis-fire/detonation that could cause this internal damage?

And are real Kubota parts still around for this engine. At the least I need a new piston and some head work. Cylinder bore looks good with no ridge.

In the Tech WIKI there is an old article about a guy in the Bay area doing a partial rebuild. The pictures of his rear piston looks a lot like mine.

prh,

There's Kubota parts manuals for the D850 block in the TechWiki > Manuals page. The PDF is text, so you can select/copy a p/n and past it into a dealer website.  I like to use www.Messicks.com -- they show you realtime parts availablility.  Note that sometimes parts are different depending the engine serial number -- that's the Kubota s/n reportedly engraved into the injector pump land (need to remove the pump to see it - I have never seen mine,) not the Universal M-25 s/n, on your (possibly missing?) engine sticker.

Which air filter/silencer do you have? 
Is your crankcase breather hose run to it? Any parts missing?

I had Skylark v-6 In college that had a lifter tick.  One day the noise disappeared.  Uh-oh.  When I pulled the valve cover, #2 intake valve was MISSING.  The split retainer had let go, the valve dropped into the cylinder with not a piece was to be found.  Only a few marks on the piston head, nothing on the cylinder walls or head.  I can't fathom the cylinder chewing up and spitting out the valve, but it did.  I didn't get into replacing the piston -- just had the valve seat ground and a new valve.  Ran like a top until I got rid of her -- that was one bug chit withdrawn from my college luck bucket.  Maybe you'll be as lucky.

I have an M-25 guy who on #3 cylinder blew/replaced a head gasket but that wouldn't seem to help you much.

-ken

[Ron Hill]

Guys : A simple check for you to do on your injectors (especially after changing one or all) - take some soapy water and put it in the injector well and run the engine.      If you see bubbles the injector is loose!!!

A thought

[Dnimigon]

I think you just had a loose injector causing all the carbon buildup. Did the engine sound kind of funny while running. I'd just make sure the valves adjusted right and injectors tight. Fire it up. It'll take a bit to clean out that one carboned up cylinder but should be fine.