What are/do Reed assemblys do in my crossflow v-4's? Learning during teardown.

Hi All,

Sure learning alot while I am taking apart a couple of Johnson 115's for rebuild the winter, a 1984 and a 1993. Whichever comes out good goes on the boat, the other will sell or keep as spare.

Just about ready to open the case, all parts are photographed & labeled to the 9th degree

QUESTION IS: What exactly do the reed plates/assm's do?

Air fuel pases them I know, but what exactly do they do? Very curious. AND is there anything to look for with the old ones? they appear very clean. ( I am following a genuine manual).


Thanks

Mark

Re: What are/do Reed assemblys do in my crossflow v-4's? Learning during teardown.

It's a one way valve.

On the upstroke of the piston there is a vacuum in the crank case, this forces air and gas into the crank case, on the down stroke the crankcase is pressurized and would force some of the charge back into the carb but the reed valve stops it from doing this, so the charge is forced into the combustion chamber.

Re: What are/do Reed assemblys do in my crossflow v-4's? Learning during teardown.

Thanks, makes sense. With the valves "closed" while the case is pressurized, what is the path for the mix to the combustion chamber....some of the cylinder ports I assume?

Sorry if this sounds picky..Just I'm sitting in front of it now on the bench, just curious how things work a bit more then I knew before.

Thanks again!!

mark

ondarvr said:

It's a one way valve.

On the upstroke of the piston there is a vacuum in the crank case, this sucks air and gas into the crank case, on the down stroke the crankcase is pressurized and would force some of the charge back into the carb but the reed valve stops it from doing this, so the charge is forced into the combustion chamber.

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Re: What are/do Reed assemblys do in my crossflow v-4's? Learning during teardown.

If you have a head off, look at the ports in the side of the cylinders. On the piston upstroke, air/fuel is drawn into the crankcase. Then on the downstroke, that charge is compressed in the crankcase. As the piston nears the bottom of the stroke, the exhaust ports are uncovered first, letting the exhaust blow out. Then a bit later, the intake ports are uncovered, and the compressed air/fuel in the crankcase is blown into the cylinder. It hits the steep side of the piston dome, which directs it toward the top of the cylinder, and at the same time the incoming charge flushes any remaining exhaust gasses out its ports. Then the piston goes on the upstroke, compressing the air/fuel in the cylinder and at the same time drawing a new charge in through the reeds.

Re: What are/do Reed assemblys do in my crossflow v-4's? Learning during teardown.

Very cool...thanks for the play by play! I looked at those suckers, trying to figure out what they did. Appreciate the help. When I take something apart I like to have some idea of what does what.

Appreciated!

Re: What are/do Reed assemblys do in my crossflow v-4's? Learning during teardown.

You have the makings of a good mechanic. Once you understand how something works, the rest is just muscle. Are you a young person?

Re: What are/do Reed assemblys do in my crossflow v-4's? Learning during teardown.

Pretty much explained correctly but.... the vacuum of crankcase does not draw in the fuel /air charge, instead the outside atmospheric pressure rushes thru carb to fill crankcase void.

Re: What are/do Reed assemblys do in my crossflow v-4's? Learning during teardown.

Faztbullet said:

Pretty much explained correctly but.... the vacuum of crankcase does not draw in the fuel /air charge, instead the outside atmospheric pressure rushes thru carb to fill crankcase void.

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this is why i love this site . so, what are some symptoms of bad reeds ? ,...i've read a few posts where you can use a flashlight to inspect them .

Re: What are/do Reed assemblys do in my crossflow v-4's? Learning during teardown.

People worry entirely too much about reeds. They are very reliable and trouble free. If they lie flat against the plate, they are ok. Unless some genius tampered with them trying to make more horsepower.

faztbullet, you are technically correct. Likewise, fuel is not sucked from the venturi of a carburetor, atmospheric pressure on the surface of the fuel in the float bowl pushes it to a low pressure area. However, things can be explained in a way that is familiar to a person's thinking. We THINK we suck a drink through a straw, but atmospheric pressure on the surface of the drink pushes it into the low pressure area in our mouth. None of these things would work in outer space.

Now...shall we discuss which direction electricity flows in a circuit?

Re: What are/do Reed assemblys do in my crossflow v-4's? Learning during teardown.

F_R said:

Now...shall we discuss which direction electricity flows in a circuit?

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Sign me up. I love it when F_R shares his "secret stuff"!

Re: What are/do Reed assemblys do in my crossflow v-4's? Learning during teardown.

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Now...shall we discuss which direction electricity flows in a circuit?[/QUOTE]

negative to posative , the reason being, it starts from 0 , and graduates one volt at a time . holy guacamoli , i'm a geek ...:lol:

Re: What are/do Reed assemblys do in my crossflow v-4's? Learning during teardown.

Now...shall we discuss which direction electricity flows in a circuit?

Click to expand...

I thought everybody knew a positive ground system was correct???

Re: What are/do Reed assemblys do in my crossflow v-4's? Learning during teardown.

Benjamin Franklin described electricity flow as positive to negative. It was later descovered that he got it backwards. Confusion has persisted ever since. There are two schools on the thought. "Conventional Flow Notation" says it flows from positive to negative, which is incorrect. "Electron Flow Notation" says it flows from negative to positive, which is the truth. Just last week I discussed this with an electrical engineer at the largest nuclear generating plant in the U.S. I was totally surprised to learn that they use the incorrect conventional flow notation in the power plant because it is the way everybody THINKS is true, and therefor is easier to understand. But if you were studying other electronics, you would have to learn the electron flow notation. For instance, the negative to positive flow is necessary to understand how the vacuum tubes work in old radios. Vacuum tubes are obsolete so don't matter, you say? Not so, until recently all television sets had at least one vacuum tube----the picture tube. The cathode in the small end of the tube is heated and (negative) electrons are released and travel at high speed to the (positive) face of the tube where they strike phosphors which glow and you see it as a picture. In fact, you may be seeing it happen right now on your computer monitor----unless you have one of the new flat screen LED ones.

Re: What are/do Reed assemblys do in my crossflow v-4's? Learning during teardown.

The largest nuclear power plant in the U.S. uses the wrong " flow notation"!? Does Homer Simpson work at that plant?

Re: What are/do Reed assemblys do in my crossflow v-4's? Learning during teardown.

To help educate those at the power plant, and to not perpetuate the misconception, I have edited my post.

We use vacuum pumps in many production processes when building fiberglass parts and this is brought up frequently, so I should have known better than to use the term "sucks", but I guess using the term does suck.

Re: What are/do Reed assemblys do in my crossflow v-4's? Learning during teardown.

HAHA, Funny stuff--See what I started??

F_R, Thanks...Not so young at 49. Been a motor guy all my life only recently began rebuilding my personal outboards. I'm slow methodical and like to know what the "mysterious" stuff in there does while I've got it apart

Thanks again!

Re: What are/do Reed assemblys do in my crossflow v-4's? Learning during teardown.

ondarvr said:

To help educate those at the power plant, and to not perpetuate the misconception, I have edited my post.

We use vacuum pumps in many production processes when building fiberglass parts and this is brought up frequently, so I should have known better than to use the term "sucks", but I guess using the term does suck.

Click to expand...

so what you're telling us is , we've been using the wrong term for centuries . but i'll stick with old school and NOT ask my g/f for a preasure job . :facepalm: