4440/4250/4450 revs on start up

4240 Turbo · Dec 14, 2019

These tractors are designed to do this, how and why? just curious.It appears to be an oil pressure related aneroid that allows the engine to rev until a certain rpm/ oil pressure/ boost is achieved then it idles to the throttle setting. Is this an oil pressure system? Mine I can kill the fuel and crank until oil pressure coes up then throw the fuelto it but it still does the rev thing. How does this system work?

Bob · Dec 15, 2019

A strong magnet in the injection pump holds the "rack" in the "full-fuel" position 'til the engine revs high enough that the governor has the strength to yank it away from the magnet. It can't get back there until after shutdown, when the little oil-operated cylinder retracts and allows the extra rack travel to get back to the magnet.

fdt860 · Dec 15, 2019

They do it more if you push the throttle for starting. If you shut them off without pulling the shut off all the way the android will not re-engage.

4240 Turbo · Dec 15, 2019

makes perfect sense that is why then. a magnet and the oil pressure let it throttle up.

Dieseltech · Dec 15, 2019

The rack magnet holds the rack full forward so the plunger retard start notch sets timing back for easier cold starts. The aneroid is disconnected from restricting rack travel until engine oil pressure comes up, then the oil cylinder shifts the bellcrank placing aneroid back into play to limit rack travel during normal use. The operator can stop the cold rev up by watching the tach, when it's close to 1000 RPM QUICKLY pull out/push back the stop control. This pulls the rack away from the magnet so engine won't rev up to 1300 plus RPM range. Some Bosch pumps use an electric solenoid to shift the bellcrank instead of the oil cylinder.

Bob Bancroft · Dec 15, 2019

This goes to a horse of a different color. If I understand this correctly, if the pump has an electric shut off, there's nothing you can do to stop that high revving?

Dieseltech · Dec 15, 2019

All depends where the solenoid is, if it's where the oil cylinder is then it's job is to shift the bellcrank after starting so aneroid will limit rack travel with no turbo boost. If the solenoid is at the front of pump it's job is to push the rack rearward for engine shutdown, plunger pulls in to allow rack to move forward for starting. No way to disable the rack magnet UNLESS pump governor has a separate stop lever, some do, but it may not be hooked up.

Dieseltech · Dec 15, 2019

That only applies to the early pumps with the "rat trap" aneroid cutout linkage. It was so troublesome the hydraulic cylinder came to replace the early design. Some owners would pull the rod out and hold it with a spring and cotter pin to hold the rod out.

r.w.b. · Dec 16, 2019

On them nippendenso pumps i pull kill cble knob out start cranking and push knob in slow.you will find the distance where it starts firing. After couple trys you get where you can start it lots easier than letting it crank wide open n fuel flood. Actually start real easy n not smoke or knock.

4440/4250/4450 revs on start up

4240 Turbo

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Bob

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fdt860

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4240 Turbo

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Dieseltech

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Bob Bancroft

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Dieseltech

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Dieseltech

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r.w.b.

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