Top Head Clearance question

[Dwarner]

Everything went very well reassembling my B1759 engine until I got to the head. The manual stated to check top head clearance to see if a head gasket shim is needed. Looks like to me once the head is on and torqued, if the piston to head clearance is under the spec. (.0237 to .0315) you need to remove the head and add the .008 shim. My thinking is if the head gasket has been torqued it should be replaced. Using a dial indicator the pistons rise .011 above the block deck. The new factory gasket presently measures about .043.
Does anyone know how much crush to expect from the factory gasket?

 

[North Idaho Wolfman]

As long as you don't run and heat the engine up you don't need to replace the gasket again.

Just don't over torque the gasket.

 

[Dwarner]

Thank you I plan on using wire solder to check the clearance through the injection port.

 

[JeffL]

Using solder is a good idea. When I do rebuilds I always save the old gaskets until new engine is together. That way I can measure the old head gasket fire ring thickness to compare to new gasket. Jeff

 

[Dwarner]

I too always save old gaskets and parts until the job is done however this tractor had work done just prior to me buying it. They had used an aftermarket head gasket that was about .060 thick crushed. The new Kubota head gasket is almost .020 thinner new. Messicks agreed that although the new head gasket is installed and removed it should still be ok to add the shim and reinstall. I'm not real comfortable with reusing a head gasket time will tell.

 

[JeffL]

I also do not reuse head gaskets once torqued. Many people do without problems. I don't because the second torque will not have the same bolt load ratio between the fire ring and body as the fire ring crushes more then the body.
This may mean little on the older B series that were very low power for their size. Newer higher HP diesels and especially over the road trucks/tractors this will mean a guaranteed failure. Jeff

 

[JeffL]

0.060" vs 0.043" Kubota !!! Unless this was a special gasket designed to compensate for block deck milling then it is blatant stupidity on the part of the aftermarket supplier. And this does occur in aftermarket parts.
Any chance you bought this tractor for hard to start & poor performance?
Jeff

 

[Dwarner]

Was told the water pump went and the engine overheated. Overheated was no where close to the temps this engine endured. Oil had to be removed with a putty knife. Cylinders warped some spots were undersized, a rebore fixed cylinders. Head is still good. All bearings were well within spec but replaced anyway. Engine temps were high enough to cause the plastic from emblem to start to melt.

 

[North Idaho Wolfman]

What engine are you working on?
As there is not a B1759 engine, or tractor??

What tractor or equipment does this fit into?

Kubota engine are:
Z or ZL 2 cylinder
D 3 cylinder
V 4 cylinder
F 5 cylinder
S 6 cylinder
and the Numbers will be CC's

 

[JeffL]

Wow. Sounds like a good deal! I'm not afraid to pull one from the coffin. Some of my favorite toys were discards. Well after considerable labor.
Success is in the details, check everything. Jeff

 

[Dwarner]

Sorry for the typo the tractor is a B1750 and the engine is the D950.

Put the head on today and checked the top head clearance and I was not happy. The clearance is .045 thousandths. Spec is approx .021 to .030
Called Messicks (great people) and they fell put it together and see what happens. If the compression isn't high enough the engine will have to be torn down again and have the block decked.

 

[North Idaho Wolfman]

Sorry for the typo the tractor is a B1750 and the engine is the D950.

Put the head on today and checked the top head clearance and I was not happy. The clearance is .045 thousandths. Spec is approx .021 to .030
Called Messicks (great people) and they fell put it together and see what happens. If the compression isn't high enough the engine will have to be torn down again and have the block decked.

It's very very uncommon to have to deck a Kubota engine, In fact it should be avoided.
Decking a Kubota block changes the fuel timing and you would have to reset the injection pump, a real pain in the back side!

If you measured it via the Injector port it's very likely that you didn't get past the pre chamber plug location and are getting a false measurement.
If you haven't taken it apart yet do a simple compression test, that will tell you if it's right.

 

[adventure bob]

NIW: don't take this as criticism and I don't think you have any omissions (LOL) asking cause I'm not getting it.

How does decking the head change the fuel timing? Isnt fuel timing still predicated on crank position?

 

[D2Cat]

When you mill the block the position of the IP is now lower. Remember those shims under the IP, they're now needs to be more.... how many, how much?

 

[North Idaho Wolfman]

D2Cat nailed it.

 

[Dwarner]

Once the engine is assembled I do plan on a compression test and attempt to run it on my engine stand.
I turned the engine over by hand with a wrench and the oil pressure easily went over 35psi.

 

[JeffL]

Wouldn't you just add the amount decked from the block to the shim pack the reach the original pump height? Jeff

 

[North Idaho Wolfman]

Wouldn't you just add the amount decked from the block to the shim pack the reach the original pump height? Jeff

Yes, but your counting on the machine shop giving you the right measurement.

It's just very very uncommon to have to deck a Kubota Block, they are not subject to the normal block issues like other engines.

 

[adventure bob]

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.

 

[North Idaho Wolfman]

Can static pump timing not be adjusted to compensate for such a small fuel timing issue?

Simple answer is nope, the timing is only controlled by shims, no other adjustment is available.

Note: This does not apply to newer mechanical injection pumps, as they do have a adjustment for timing of the individual injection pumps.