It's the little things......

[Simondo]

The 7900/7910 transfers are bottom fed so not as dependent on the piston windows. Not sure why they used the earlier design.

The 242 however is side fed so the windows play a much bigger role. If you're stuck with using the non windowed piston it might help to drag/grind the 242 lowers down as much as the base/skirt allows.

I see what you mean.... that would explain the 5105 having the same sort of new piston as the 7910, its (Dol 5105) configuration is so similar (by sight) to a Husq 346 and that uses a none windowed piston.
I would have liked to use the Meteor for the 242 xp but in the end after "Much" searching i went down the rout of a "Golf" piston that was windowed . The Meteor is good for the 42 special as that is "none windowed " from factory.

 

[wcorey]

The Meteor is good for the 42 special as that is "none windowed " from factory.

Though the 42 is open port, it's also side fed.
I have to wonder if the windowed piston could have an advantage there.

 

[Wilhelm]

I don't know, visually I like the beefy windowed PS-7900 piston more!
The PS-7910 piston looks kinda weak?!

But I'm not a porter and I am more than satisfied with my PS-7900's stock performance.

 

[Jon1212]

@Mastermind when I saw the Thread title I naturally thought it would be about your legs dot dot dot

 

[Simondo]

Though the 42 is open port, it's also side fed.
I have to wonder if the windowed piston could have an advantage there.

Yup ..it is open port .I did try a windowed in one but i couldn't tell any difference in standard form .
Pic of OEM Gilardoni piston &cylinder.

 

[drf256]

The jugs are the same design.......with the exception of the exhaust port (because of the muffler change) and the port widths. The way it feeds from the bottom is the same. The non-windowed piston seems to be to provide more primary compression, and better direction to the transfer charge.

How?

Seems like the old style windowed slug has much more mass below the ring.

 

[Deets066]

How?

Seems like the old style windowed slug has much more mass below the ring.

I was wondering the same thing Doc. Must have to do with the windows

 

[Mastermind]

How?

Seems like the old style windowed slug has much more mass below the ring.

I was wondering the same thing Doc. Must have to do with the windows

Yes......because of the windows.

Like holding a cup upside down under water. The entire area inside the skirts will displace volume.

 

[Deets066]

Yes......because of the windows.

Like holding a cup upside down under water. The entire area inside the skirts will displace volume.

 

[mdavlee]

I was wondering the same thing Doc. Must have to do with the windows

Windows will flow out the windows dead heading into the cylinder wall on a bottom feeding jug. Just wastes the charge with the most pressure. You can feed that with a well placed hole to match the window and feed into the upper or a finger port or boost port.

 

[Deets066]

They have the new design piston in the smaller saws as well? Or is the 7910 the first?

 

[Simondo]

They have the new design piston in the smaller saws as well? Or is the 7910 the first?

Its in the 5105

 

[drf256]

Windows will flow out the windows dead heading into the cylinder wall on a bottom feeding jug. Just wastes the charge with the most pressure. You can feed that with a well placed hole to match the window and feed into the upper or a finger port or boost port.

Excellent

Guess it matters how deeply the piston goes down into the case as well?

Looks like the new piston could be a good candidate for the Mike Lee ring pin through the crown method.

 

[mdavlee]

Excellent

Guess it matters how deeply the piston goes down into the case as well?

Looks like the new piston could be a good candidate for the Mike Lee ring pin through the crown method.

That is important. It's nice if you have a case half with crank mounted to check it all out on.

That's one way to do it.

 

[junkman]

Will the lighter piston be a loss for tourque running a 32 inch bar ? With a short bar i can see a speed increase,but what if you like an engine that keeps chugging under more load,like a heavier flywheel does ?

 

[Mastermind]

Will the lighter piston be a loss for tourque running a 32 inch bar ? With a short bar i can see a speed increase,but what if you like an engine that keeps chugging under more load,like a heavier flywheel does ?

I don't think piston weight affects the torque like a flywheel would. It's reciprocating weight rather than rotating mass.

 

[P.M.P.]

My MMWS 7910 is my favorite saw.

 

[Deets066]

Will the lighter piston be a loss for tourque running a 32 inch bar ? With a short bar i can see a speed increase,but what if you like an engine that keeps chugging under more load,like a heavier flywheel does ?

Lighter piston will gain with any bar