Top Head Clearance question

Kubota Newbie · Feb 2, 2018

Once you deck a block you can't put it back. If it ran before it will run now if reassembled properly.

Besides, something is off in Denmark!
You said that (in earlier posts):
Measured piston pop-up is .011
Un-crushed new gasket was .043
So all things being kosher the piston to head clearance HAS to be something a little less than .032 with gasket crush.
Yet... you measured and got .045 which is more than the gasket.
So, either the piston's don't pop-up, or, your measurement is off.

The piston to head clearance should really be measured/calculated at the c/l of the wrist pin. Otherwise when using something "stiff" like solder the piston "rock" will cause your measurement to be high. The amount of rock can be significant if reusing old pistons on honed cyls. or if the shop got a little on the big side with the bore/hone job.

Dwarner · Feb 2, 2018

I agree the crush clearance is way higher then I figured however after using a piece of solder on the flat surfaces between the valves and cranking the engine slowly by hand all the head clearances were high. I did this without the push rods installed. Compression pressure with a harbor freight tester tonight showed all cylinders at between 275 and 300 psi not sure how accurate the tester is. I plan on reinstalling the engine when time permits and see if it will fire. Unfortunately this engine was severely overheated and worked on before I got it possibly I missed something.

Lil Foot · Feb 2, 2018

showed all cylinders at between 275 and 300 psi

Sounds pretty low to me.... I thought 340 was about minimum for these small diesels....

Dwarner · Feb 3, 2018

When I checked the head for flatness I did not put the straightedge across the combustion chambers which extend above the surface of the head. Is it normal for the combustion chambers to be above the head surface or should they have been flush? The manual says to stay away from the combustion chambers.

North Idaho Wolfman · Feb 3, 2018

Dwarner said:
When I checked the head for flatness I did not put the straightedge across the combustion chambers which extend above the surface of the head. Is it normal for the combustion chambers to be above the head surface or should they have been flush? The manual says to stay away from the combustion chambers.

Yes it is normal for them to protrude from the head slightly, doesn't effect it.
You can't get accurate pressure tests without the valve train working.
If you put new rings in it, it going to take a few hundred rotations before they seat fully.
Also if you put the solder where the valve is you won't get an accurate measurement, it would need to be between the flat of the head and the piston.

Dwarner · Feb 3, 2018

Yes the valve train was in and adjusted for the compression check. The engine cranked a bit slower than I would have liked using jumper cables. The solder was also positioned between the valves on the flat of the head.
Just looked at the after market head gasket I removed when the engine was first disassembled. The impression in the gasket where the combustion chambers sit was about .008 impression.

eserv · Feb 3, 2018

adventure bob said:
Can static pump timing not be adjusted to compensate for such a small fuel timing issue? To put him right in the middle of his measurement were talking decking by .018". That's going to be less than 1/2 of 1 degree in timing. We could figure out exactly what it is but I don't have the specs on one of these motors to do the math.

Not trying to make an argument for him to go have the head decked, just trying to get through the rationale for the complications of one of these tractor motors.

Every .006 is about 1.5 degrees. It appears to me that the piston protrusion is on the low side at .011, should be about .5 mm or .020. the engine could easily have bent rods if it was overheated. using the provided measurements, if you assemble it without the shim the top clearance will be slightly higher than max spec. this will make it a hard starting engine and these were hard enough starting to begin with but it will likely run OK otherwise. To clarify this post I'm suggesting to NOT use the shim! The shim will make the top clearance even greater when it is already above spec! as op noted spec is .0237-.0315. If the gasket compressed to minimum it would be .0413 giving clearance about max spec.

Dwarner · Feb 4, 2018

I want to thank everyone for their comments and suggestions.
Yesterday I installed the engine back into the tractor figuring it is easy to remove the head and get the machine shop resurface it. While the glow plugs were still out the injection system was bled. All of the other connections were buttoned up but the radiator and front end will be another day. The glow plugs were warmed up for about 20 seconds cranked the engine for a couple seconds and it fired right up. The engine ran rough for a second belched a ton of smoke and smoothed right out. Guess my worries of the top head clearance and possible low compression were for nothing. Now to put the rest of the tractor together and see what else doesn't work.

eserv · Feb 4, 2018

Dwarner said:
I want to thank everyone for their comments and suggestions.
Yesterday I installed the engine back into the tractor figuring it is easy to remove the head and get the machine shop resurface it. While the glow plugs were still out the injection system was bled. All of the other connections were buttoned up but the radiator and front end will be another day. The glow plugs were warmed up for about 20 seconds cranked the engine for a couple seconds and it fired right up. The engine ran rough for a second belched a ton of smoke and smoothed right out. Guess my worries of the top head clearance and possible low compression were for nothing. Now to put the rest of the tractor together and see what else doesn't work.

Glad it worked out for you! The clearance is right near recommended so I'm sure lots of them came from the factory like that! The D950 need more glow time than the newer engines when cold but they are very reliable engines and give years of service! I have one in a Cushman mower with almost 4000 hrs and it still starts and runs well and uses no oil. It was used commercially before I got it to mow grass for a small town

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