Bobcat MT52 mini-loader engine question

Craftsman Garage

Craftsman Garage

Well-Known Member
I'm currently working on a bobcat MT52 mini loader with a Kubota D722 engine. It came in blowing white smoke from a blown head gasket. Tearing it down, found some abnormal wear on cylinder 2 where I suspect coolant was leaking into. This engine does have around 2000 hours and the head gasket was MLS. Cylinder #2 has this black discoloration and scratches that you can feel with your fingernail. Would this be the piston skirt causing this? It was bought from a landscaping company about 100 hours ago, when head gasket was not blown and ran perfectly fine.
IMG_6420.jpeg
 
I am leaning more toward the coolant steam cleaning the oil off of the cylinder walls leading to a lack of lubrication failure. Skirt to cylinder wall damage would be perpendicular to the crankshaft, but in this case the cylinder damage is all the way around the cylinder suggesting lack of lubrication.
 
ILENGINE said:
I am leaning more toward the coolant steam cleaning the oil off of the cylinder walls leading to a lack of lubrication failure. Skirt to cylinder wall damage would be perpendicular to the crankshaft, but in this case the cylinder damage is all the way around the cylinder suggesting lack of lubrication.
Click to expand...
Thank you for your input, I didn't think of that. What would the dark coloring be?
 
Hello CG,

If you or the customer plan on keeping this and getting more use out of it, it will take more than a head gasket. If they just want to "flip it" clean it up and put a head gasket on it, but I advise you to not offer any warranty at all.

If it is a keeper, I recommend you pull the pistons, hone the cylinders and re-ring this engine. It may also be a good time to replace the rod inserts if they are scored up or showing excessive wear.

The black line in the cylinder suggests the upper rings are broken from overuse of starting fluid at some point. The piston skirt does not travel that high up into the cylinder.

The second cylinder with all the fine vertical scuff lines suggests fuel thinned oil and poor oil changes along with the compression rings being weak.

These small diesel engines are more forgiving than their gas engine counterparts
 
This engine is cheap to rebuild with new pistons and liners. You don't hone the cylinders you replace the liners. Hardest part of the job is pulling the liners. Tool off ebay around $100
www.ebay.com

Overhaul Rebuild Kit for Kubota D722 Engine B7300HSD B7400HSD BX1800D BX1850D | eBay

Fit for Engine: Kubota D722, D722EBH, D722E, D722E-BX, D722E-GX. 1 Set of Overhaul Gasket Kit. 1 Set Valve Guides. 1 Set Intake/Exhaust Valves. 1 Set of Thrust Washer. 1 Set of Rod Bearings. 1 Set of Main Bearings.
www.ebay.com
 
It is difficult to tell that this engine has liners. I'm used to larger tractor engines where they are more pronounced.

Sounds labor intensive just trying to get it all removed and torn down, but these machines are not cheap to replace either.
 
Auto Doc's said:
It is difficult to tell that this engine has liners. I'm used to larger tractor engines where they are more pronounced.

Sounds labor intensive just trying to get it all removed and torn down, but these machines are not cheap to replace either.
Click to expand...
I don't think it does. The engine had to be bored to install them.
 
So basically, it is a kit to install dry liners. I would be concerned about the original bore walls being too thin after the procedure. I hope you have a good machine shop with an up-to-date boring table that is kept in calibration.
 
You must log in or register to reply here.
Back
Top