mid '80's compact 750

[DrewL]

mid \'80\'s compact 750

When turning the key to the left for the pre-heat feature, what is working? What does this 3 cylinder diesel have for it's pre-heat?

Drew

 

[DK35vince]

Re: mid \'80\'s compact 750

My 850 has a glow plug in the intake manifold that heats a small amount of fuel to help in starting.
There is a small canister on top of the intake manifold that supplies fuel to the intake to be heated.
I believe the 750 has the same setup..

 

[EquipmentJunkie]

Re: mid \'80\'s compact 750

The Deere 750 has an indirect injection diesel with glow plugs. What does this mean? Let me use an analogy to explain how it works:

Imagine that each cylinder's combustion chamber as a bedroom. A direct-injection diesel has just a bedroom. But a indirect-injection diesel has a slightly smaller bedroom with the addition of a closet. It is in this closet where the glow plug and fuel injector reside. The theory is that the glow plug will more efficiently heat this closet as opposed to the whole bedroom. This is a very simplified explanation with some holes in the analogy.

 

[Davey K]

Re: mid \'80\'s compact 750

my 1981 JD 750 with a yanmar diesel has a thermostart not glow plugs. go to Hoye Tractor Parts.com and they will explain how it functions

 

[airbiscuit]

Re: mid \'80\'s compact 750

my 1981 JD 750 with a yanmar diesel has a thermostart not glow plugs. go to Hoye Tractor Parts.com and they will explain how it functions

Huh? How about posting a direct link?

 

[airbiscuit]

Inside a Yanmar thermostart (glow plug) unit.

Inside A Yanmar Thermostart

What is a Thermostart?

A Thermostart is a very efficient glow plug used in most of the Yanmar tractors. Instead of relying on just a heating coil like other glow plugs- this unit also drips a small amount of diesel fuel (fed from a small plastic container mounted just above it) onto the red hot coil. This produces thick smoke, lots of heat, and occasionally small flames. All of these things help the engine to start in the coldest weather.

So how does it work?

The fuel line is connected to the thermostart through the fitting (A). The fuel is not allowed to leak out because the set screw (C) is screwed up into fitting (A) and is tightened up against the check ball (B) - forcing it against the ball seat deep inside fitting (A).

When you are ready to start the tractor the glow plug gets energized through the terminal (D) and heats up the element (F). This causes the hollow tube at the bottom of (A) to expand. When the tube expands it also pulls the set screw away from the check ball (B) because the set screw is threaded into the tube that is expanding. This allows a very small amount of fuel to drip down onto the heating element which starts to smoke and burn.

Why do they go bad?

Over time the thermostarts, just like any glow plug can go bad. This is typically because the heating element, which is sort of like a very heavy duty light bulb, burns out. The check valve can also start to leak over time. Running the thermostart for too long (over 10-15 seconds) at one time can also damage it.