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Full-Circle Crankshaft in Stihl Chainsaw

Mastermind

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the swirling effect would be going in the wrong direction to aid the transfer action up the front.
Not in the mental image I'm seeing. The top of the crankshaft.....spinning rapidly toward the front....intake charge enters directly on top of spinning crank.....propels charge toward the front transfer entrance.
 

Stump Shot

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Not in the mental image I'm seeing. The top of the crankshaft.....spinning rapidly toward the front....intake charge enters directly on top of spinning crank.....propels charge toward the front transfer entrance.
Picture a fan blower housing from a home furnace or some such thing, now picture that same fan trying to run in reverse rotation. That's what I'm picturing.
 

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Mastermind

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Picture a fan blower housing from a home furnace or some such thing, now picture that same fan trying to run in reverse rotation. That's what I'm picturing.
Reverse rotation? The top of the crankshaft is spinning forward. The intended direction of the intake charge is forward across the top of the crank toward the transfer entrance. Where is anything in reverse in this situation?

Maybe my mind is cooked from years of alcohol and drug abuse, but I don't see anything being in reverse in any way.
 

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Reverse rotation? The top of the crankshaft is spinning forward. The intended direction of the intake charge is forward across the top of the crank toward the transfer entrance. Where is anything in reverse in this situation?

Maybe my mind is cooked from years of alcohol and drug abuse, but I don't see anything being in reverse in any way.
Well, the transfer is going up and the crankshaft is spinning in a downward direction. It would be more natural this a way, instead of having to be forced fed into it. No?
 

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Well, the transfer is going up and the crankshaft is spinning in a downward direction. It would be more natural this a way, instead of having to be forced fed into it. No?
Modify the image you posted in your mind. Close off the sides. Take away that outlet. Now just open a window on top. Now its not pulling air down into the fan housing....its just assisting the air travel across the top of the fan.

That's how I see it at any rate.
 

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Modify the image you posted in your mind. Close off the sides. Take away that outlet. Now just open a window on top. Now its not pulling air down into the fan housing....its just assisting the air travel across the top of the fan.

That's how I see it at any rate.
This is what I conjured up when the pea rolls around again.
IMG_20230419_093052974.jpg
Not to scale. Lol
 

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This is what I conjured up when the pea rolls around again.
View attachment 374534
Not to scale. Lol
At one time, I saw it the same way. But...

What your drawing is leaving out is the location of the intake spigot. It enters above the crankshaft, and at an angle that would make it very difficult for the flow to follow the counterweights down into the case. The flow would have to do a 180 change in direction. Instead, the incoming charge simply follows along the top of the spinning crank to the other side. I believe once it gets there, it experiences a pressure increase that pushes it into the transfer inlet.
 

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At one time, I saw it the same way. But...

What your drawing is leaving out is the location of the intake spigot. It enters above the crankshaft, and at an angle that would make it very difficult for the flow to follow the counterweights down into the case. The flow would have to do a 180 change in direction. Instead, the incoming charge simply follows along the top of the spinning crank to the other side. I believe once it gets there, it experiences a pressure increase that pushes it into the transfer inlet.

I get what you're laying down.
 

Al Smith

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If I recall notched counter weights have been experimented with in the hopes of somewhat internal super charging but with little success .
 

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7900 always makes me scratch my head, it’s a very tight case, tight trans, tight every port really, and torque for days!
That's why it has torque. Even as the rpms fall, it's still able to flow air from crank to cylinder with more velocity due to the tighter ports. The air is not as lazy.

But, I might be more than wet behind the ears.
 

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At one time, I saw it the same way. But...

What your drawing is leaving out is the location of the intake spigot. It enters above the crankshaft, and at an angle that would make it very difficult for the flow to follow the counterweights down into the case. The flow would have to do a 180 change in direction. Instead, the incoming charge simply follows along the top of the spinning crank to the other side. I believe once it gets there, it experiences a pressure increase that pushes it into the transfer inlet.
This is very similar to how I think about it. When the intake opens the weights are on the other side of the case. They reach the intake around the same time it’s closing. They should carry charge to the exhaust side very well. I have a theory that the leading face of the crank weights has a higher pressure zone than the rear. Kind of like an airplane wing or a semi truck driving down the highway. There’s a pressure wave that blows past the transfer lower like when you get passed by a semi and blown to the side. With a full circle the wave is less distinct but there is still a drag layer around the outside of the circle.

If I recall notched counter weights have been experimented with in the hopes of somewhat internal super charging but with little success .

This is another area where quality experiments need to be done. There’s weak evidence in both directions with enormous variation in design.
 

nbbt

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Didn't the op's location originally have Oregon as a location, now it's England with a USA flag.
 
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