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.

 

[Jtullis13]

Its not only for prelube, it also reduces the stress on the starter, battery and bearings with the oil being circulated. And maybe they saw something that we didn't at the time they were producing these engines

 

[Industrial Toys]

I know, many old big generators used to have a hand pump, for prelube. You never see that anymore. Everything is just so disposible, and that's the way the manufacturers like it.

 

[Jtullis13]

I know, many old big generators used to have a hand pump, for prelube. You never see that anymore. Everything is just so disposible, and that's the way the manufacturers like it.

Well you pretty much hit the head on the nail! Back in the day they made things to last a long long time, and now most things are made to be disposable, and that is how a very large portion of the population thinks too, "ehh I will just get a new one" and pay the money for it. I consider my self like most others on here a "dying breed" we fix the things we have and take pride in taking care of our things too (our tractors) so they last us a life time. But manufacturers want us to throw away and get new. I just hate that and hate how people think thats acceptable

 

[Industrial Toys]

You are right except for one thing. They generally don't pay for it. All the flyers I get from Kubota only STRESS financing and low payments. No price mentioned on anything.

And oh so many discard good old stuff for incredibly cheaply made "NEW" stuff.

Remember when almost all air filters were oil filled? You washed out the canister or washed a foam element in gasoline (oh the horror). One less thing where you were reliant on someone else, like a dealer or store.

 

[Jtullis13]

True they don't mention the price, but they pay for it in the financing. And a lot of people don't take the time to figure out how much more they are actually paying either.

And yes many discard old stuff, or what they consider old stuff and people like us and the others on this forum are here to nab it up and make it useful.

 

[kenmac]

from the manual.. ''The decompression lever is used to assist the capacity of the battery and starter motor when starting the engine''

 

[clemsonfor]

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.

The first part of your post is what most of us use it for not what's posted in the manual.

Your second statement is true that's why there is a decompression lever?

 

[Industrial Toys]

Does the average oil pump even move any oil at cranking speed?

I made a prelube system for one of my generators, without success. I found it had to be quite a pump.

 

[clemsonfor]

True they don't mention the price, but they pay for it in the financing. And a lot of people don't take the time to figure out how much more they are actually paying either.

And yes many discard old stuff, or what they consider old stuff and people like us and the others on this forum are here to nab it up and make it useful.

Yea man, I end up with so much "junk" and stuff not worth fixing that I use it for years after or sell!

My latest prize was my ZT mower. Airens brand 42" welded deck. Buddy said it had been leaking oil for years and it caught fire he was done with it. I have less than $100 bucks in it. I wouldn't have that much if he didn't trash the motor shroud and air filter cover that I had tO buy off ebay. Ended up putting a new bushing and wheel bearings in one front caster, new air filter, did both head gaskets , replaced the plastics on it, changed the oil and hydro oil and filters on it adjusted the steer levers. Now it's good to go!

 

[CalG]

A compression release is a great fall back in the event of a run away condition.