4020 recent overhaul but running away down hills

[Jhun]

Have a JD 4020 diesel synchro range (serial #201,000-) that we overhauled this past winter with JD parts. It received new pistons, rings, sleeves, and injectors, and we also had the head machined and cleaned. The tractor starts quickly and runs well but with a lightly loaded wagon behind the tractor (maybe 4K lbs) the engine will run away a bit down a hill, with the throttle at idle it went up to 1700 rpm on me but then at the bottom on the hill would then slow to an idle again. The valves and seats where not replaced in the overhaul and from research Ive done thinking this could be the issue? Also read that the fuel pump could be the problem but oil looks normal and fine. If anyone has any insight of what to check or what the problem could be I would very much appreciate the advice!

 

[Le9102011]

I think that's a normal operating characteristic. Unless you push in the clutch when you go down the hill as you pick
up speed your engine RPM's will do the same even though its at idle, same principle when a truck driver comes down a
hill in lower gears the RPMS will climb up and give engine braking effect even though they arent touching the
accelerator.

 

[nlastovi]

By their nature, diesel engines in provide little engine braking as they are not equipped with a throttle body and thus cannot draw a vacuum in the intake manifold. During the compression stroke on a diesel, energy is used as the upward-traveling piston compresses air in the cylinder; the compressed air then acts as a compressed spring and pushes the piston back down. Any braking that happens is due to friction losses within the engine and drive components (such braking might be consequential).

 

[Jhun]

We have 2 other 4020s that we also pull the same wagons with on the same path and those two may only go up 100rpm or so on the same slope, this particular one is 10x worse where it will run 1000rpm higher than the throttle is set to. I do believe compression is being lost somewhere as this one acts so differently than the other two.

 

[MikeJM]

Dieseltech would know better, but Ive heard that a worn metering valve in the roosamasters can cause that.

 

[Jhun]

(quoted from post at 20:33:24 08/09/21) Dieseltech would know better, but Ive heard that a worn metering valve in the roosamasters can cause that.

Thank you, will check that out

 

[Dieseltech]

Stanadyne/Roosa pumps have a standard and oversize metering valve available, if the hydraulic head needs the oversized valve and a standard is used that will cause what you describe due to excessive fuel leakage past the valve.