Diesel Newbie

[Semper Fly]

I'm new to diesels and I don't have a clue what the Decompression Release does.

Can anyone clue me in?

 

[DavidNPro]

I'm new to diesels and I don't have a clue what the Decompression Release does.

Can anyone clue me in?

It is used to prevent the engine from creating pressure while it is turning over. In turn, it allows the engine to spin over much more easily and prevents it from starting. It is often used to allow the engine to build oil pressure before starting.

For example, you would pull the compression release, turn over the tractor until it has oil pressure, release the compression release and then start that tractor.

 

[deepNdirt]

I'm new to diesels and I don't have a clue what the Decompression Release does.

Can anyone clue me in?

Welcome to TBN..... You're sure to find answers to all your questions here,
to try and answer the one about "decompression" it can be used for a couple of things,
1- as the weather gets colder in some parts of the country the oil in the engine can thicken, causing the engine not to be turn over as easily as would be in warm conditions, the decompression lever can be used to spin the engine over more freely,
also helps to pre-warm the cylinders by creating rapid friction from the piston & rings,
I'll let the other members elaborate further

 

[Gary Sweat]

I've found that it's about the only way I can start mine if the temperature gets below about 50 degrees. I don't have glow plugs. Sometimes I have to pull it a couple of times. I would think it would help extend the life of the starter as well??

 

[Semper Fly]

Thanks for the replies guys. I couldn't ask for a better response and thanks for clearing that up for me.

 

[California]

And I'll add my 2 cents worth (mostly repeating what was already said):

These things have higher compression than a gas engine and heavy flywheels. It is gentler on the starter to bring the flywheel up to full speed, if it doesn't hit a compression stroke immediately.

And after the flywheel is spinning freely at maximum speed and you drop the compression release, the flywheel's inertia assists the starting motor in overcoming the resistance of compression. So that first compression stroke is accomplished at higher rpm. In cold weather with a chilled battery this inertia may make the difference between start on the first stroke/give up and try again.


2) For these rice-paddy tractors I wonder if the compression release is also intended to get the water out of the cylinders without damage after the operator underestimated the depth he was driving into.

 

[normde2001]

It's a manual version of the automatic compression release on a lawn mower engine.

 

[stormpetrel]

Welcome Semper! What tractor do you have?

I have a follow up question: can the engine start at all while the compression release is engaged, or does it start after it's dis-engaged? It's the compression that causes combustion, yes? I don't see how the engine can fire with NO compression. Thoughts?

 

[California]

It holds the valves open so the engine spins freely with no compression. You have to let go of the lever/cable/whatever to allow compression, and therefor starting.

For an example go to my page referenced from my sig, below, scroll to the bottom, and listen to the sound file.

Edit:

Here's a direct link to that sound/vid.

Sound file of cold weather start, warmup @ 1500 rpm as recommended in the manual, the Yanmar Hammer (fuel knock) racket at idle below 1000 rpm, and finally 1050 - 1100 working rpm to lift the implements and pull out of the barn.

(If you're at work turn it up LOUD!)

 

[Gary Sweat]

Welcome Semper! What tractor do you have?

I have a follow up question: can the engine start at all while the compression release is engaged, or does it start after it's dis-engaged? It's the compression that causes combustion, yes? I don't see how the engine can fire with NO compression. Thoughts?

I'm no diesel mechanic but from observing my tractor, it is apparently letting the fuel sucked in on the intake stroke just go out the exhaust. Lots of nice gray/bluish smoke till you let go of the release. I've actually gotten in the habit of using it all the time to start the engine. Hope that is not leading to problems down the road

 

[jonyyuma]

Assuming it is spinning and building oil presssure, what harm could be expected. It is priming for combustion in a simpler term? Unless your fuel has gelled and is not spraying properly, it should promote running.? Jy..

 

[deepNdirt]

Gary, it doesn't hurt a thing to crank it the way you are doing, without the glow start not working you have no other choice, Basically as I stated before you are creating friction/heat in the cylinder this helps,.... but what ever you do!
do not start using starter fluid/ether on it, this is very risky and hard on the engine,
perhaps its time should do a copmression test on the cylinders,

 

[IslandTractor]

The compressuion release can also be used to stop a diesel. I have had marine diesels where that was the routine and only way to stop the engine. It can also be used to shut down a runaway diesel.

 

[normde2001]

The compressuion release can also be used to stop a diesel. I have had marine diesels where that was the routine and only way to stop the engine. It can also be used to shut down a runaway diesel.

My YM240 ops manual says "DO NOT" use the decompression lever to stop the engine. I suspect they all do.

 

[Semper Fly]

StormPetrel,

I have a FX20D with a Koyker 120 FEL.

 

[winston1]

Welcome Semper! What tractor do you have?

I have a follow up question: can the engine start at all while the compression release is engaged, or does it start after it's dis-engaged? It's the compression that causes combustion, yes? I don't see how the engine can fire with NO compression. Thoughts?

Don't think it has been stated but release only holds down exhaust valves. The engine will not crank with decompression pulled which is the wanted result. Oil pressure and rpms are accomplished before the big bang that you hear on California's vidio.

 

[IslandTractor]

My YM240 ops manual says "DO NOT" use the decompression lever to stop the engine. I suspect they all do.

Interesting as the only way to stop the Yanmar 3GM marine engine was through decompression. I don't see how it would be harmful as it simply prevents combustion.

It was also possible to use the decompression levers independently so with a weak battery or manual crank you could get some momentum on the flywheel and then compress only one cylinder to get the motor running.

 

[winston1]

The injector pump will still be pumping fuel if you kill it with the decompression. Not saying it will hurt anything, but really don't understand why using the decompression over turning the fuel off could be better.

 

[stormpetrel]

StormPetrel,

I have a FX20D with a Koyker 120 FEL.

Nice rig. So, our tractors are very similar, yes? you have powershift and a 24 hp + - engine, and the same loader I do. All the F models are 3 cyl though, where mine is 2.

 

[IslandTractor]

The injector pump will still be pumping fuel if you kill it with the decompression. Not saying it will hurt anything, but really don't understand why using the decompression over turning the fuel off could be better.

I'm not a diesel engineer but I recall the 3gm had a mechanical fuel pump as it was possible to run the engine with no battery (if memory serves). I think the old Saab one lunger was like that too.