What is the correct use of the decompression/compression release knob?

[Bluest]

I use the compression release, with the fuel shut off, to spin the engine and circulate some oil before starting. I guess that is not its real purpose though, so what should I be using it for?

 

[Jtullis13]

I use the compression release, with the fuel shut off, to spin the engine and circulate some oil before starting. I guess that is not its real purpose though, so what should I be using it for?

What do you mean that is not the real purpose? You are suppose to turn the decompression lever with fuel off and turn the engine over until you build up oil pressure or at least have some oil circulating to get to your crank, bearings ect. The decompression lever also allows you to turn the engine over easier with out starting, this makes things easier on your starter, bearings and battery especially when it is cold out. You can also use the lever if you are working on your engine and wanting to get it to top dead center, it would make it easier to turn by hand. I use mine no matter if it is warm or cold out.

So what did you think it was used for? Just curious

 

[Bluest]

Well, what you describe is what I use it for, but only because I thought it was a good idea, I never read that anywhere. But, I only really do that when it has been sat for a while, not every time.

I’d sort of though it may actually be used to aid starting somehow, like on big kick start motorbikes, but as I don’t have any starting problems, I didn’t give it any more thought than that.

 

[Jtullis13]

You are using it appropriately, and I would keep using it that way. Do you have to use it every time, well that is up to you. I do catch myself not using if I just shut it down in and going to start it again in the next hour, otherwise I use it pretty much all the time.

 

[thepumpguysc]

I don't see any harm in using it that way.. but its used for starting.. u get the engine spinning fast to create heat so the fuel from the injectors will "catch fire" & the engine will start..
Some people use it to shut down the engine.. which ISNT what its for..

 

[Industrial Toys]

I doubt you get much heat with no compression. It just allows you to get the engine up to speed so the momentum will allow compression when the lever is released. Never heard of the oil pressure question.

 

[normde2001]

I use the compression release, with the fuel shut off, to spin the engine and circulate some oil before starting. I guess that is not its real purpose though, so what should I be using it for?

I use mine the same as you, only on cold starts til oil light goes out, (about 2 sec.). My tractor starts almost instantlly so no need to waste starter building revs.

 

[Industrial Toys]

I have only used one on my single cylinder Yanmar air cooled. Do they release compression on all cylinders via some kind of linkage.

 

[Jtullis13]

I use mine the same as you, only on cold starts til oil light goes out, (about 2 sec.). My tractor starts almost instantlly so no need to waste starter building revs.

The decompression lever has linkage that attaches to the exhaust valves on the engine, when the lever is pulled or turned it opens up the exhaust valves resulting in minimal to no compression and for the engine to turn over very easily and for the oil pump to circulate oil prior to starting the engine.

 

[Industrial Toys]

I wonder why they find it necessary to prelube the engine when no one else seems to think it's important.

I would think it is far harder on a starter to make compression on it's own, than spin an engine without compression and let the flywheel do the work.