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ID cylinder.

wcorey

wcorey

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A 51 piston should work but since it’s designed for open transfers and lacks windows you will need to grind out the bottoms of your cylinders lower transfers so they function as bottom fed rather than side fed.

There’s pictures of this process in a few various threads, you’d have to search a bit to dig them up. Might be for different saws such as Jred 490/590 or partner 5000 but still applicable for the 55.
 
Huskvarna hotellgäst

Huskvarna hotellgäst

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Huskvarna hotellgäst

Huskvarna hotellgäst

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A 51 piston should work but since it’s designed for open transfers and lacks windows you will need to grind out the bottoms of your cylinders lower transfers so they function as bottom fed rather than side fed.

There’s pictures of this process in a few various threads, you’d have to search a bit to dig them up. Might be for different saws such as Jred 490/590 or partner 5000 but still applicable for the 55.
I'm skeptical about this. On a 5000+ or Husky 154/254, there's no unnecessarily thick lower transfer to be ground out. The outside wall of the port follows the curve in the inner sand/glass mould very closely and even with that, the starter side is ground to clear the flywheel.
 
cus_deluxe

cus_deluxe

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Huskvarna hotellgäst

Huskvarna hotellgäst

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this is what i did to my 5000 cylinder. as i said earlier, i just drilled holes in the piston that came originally on this 50, 44mm open port. i opened up the lowers the way bill mentioned.
View attachment 730373 View attachment 730374
Clearly it must be doable...because you did it! :)
Looking again at the Mahle 154 cylinder in front of me, there's not much "meat" near the base around the transfers. You must have patient, steady hands.
 
Huskvarna hotellgäst

Huskvarna hotellgäst

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Skeptical is ok.
I'm quite certain it's easily doable, has been done and has been documented.
There's speculation that it runs better that way than the stock piston.
I plan to do a few myself.
Without getting into inertia, eddies & boundary layer technicalities, the short, curved, reducing cross-section transfer ports in the 5000+ and Husky 444, 162, 154, 262, etc, are more expensive to make than finger ports. They're made that way in order to deliver maximum mixture at high rpm and so maintain the highest possible chain speed under load.
Lengthening them may move the torque peak lower in the rev range, which could indeed make the saw feel more powerful...or "better", in your hands.
 
wcorey

wcorey

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Without getting into inertia, eddies & boundary layer technicalities, the short, curved, reducing cross-section transfer ports in the 5000+ and Husky 444, 162, 154, 262, etc, are more expensive to make than finger ports.
Not sure of your direction on this with the reference to 'finger ports' but just to be clear we're not talking open port vs closed port here.
Factory bottom fed design on closed port transfers has been common practice on many models of very high revving/high output saws, more particularly with quad ports but there are also many examples done in dual port configs. Some were even factory recommended 'performance upgrades' that were implemented by dealers on new saws.
This is nothing new...

They're made that way in order to deliver maximum mixture at high rpm and so maintain the highest possible chain speed under load. Lengthening them may move the torque peak lower in the rev range, which could indeed make the saw feel more powerful...or "better", in your hands.
I don't see this as something that would significantly move the peak torque down in the revs, though that it adds a bit more crank case volume may have that effect to a degree.
You could also look at this mod as feeding the lower transfer in a more direct/uninterrupted path rather than having to convolute in from the side through the piston windows. Six 'o one, half doz 'o the other...
Yes there are some new flow dynamics but the entry and exit angles of the uppers remain largely unchanged.
 
muddstopper

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I was scroungeing a old repair shop the other day and saw a open port piston sticking out of a old 55 case. Outside in the rain and ring is rusty. I knew it was a 45mm when I saw it because the 46mm piston doesnt look the same. Anyways, didnt look real close, but the ring was still on the piston so I asked about getting it. The old guy gave it to me. Now whether or not the piston is useable or not, I havent even dragged it out of the back of my truck. I have 2 open port cylinders I got in a box of junk about a year ago and might try to put one together. Or I might could be talked out of the parts, I need a oe 346xp case. dont need a whole saw, just the 2 case halfs. Might even settle for just the flywheel side. Thats the side I broke when I knocked it off my bench.
 
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