HELP! Understanding piston design

[STOVE]

Can someone explain the piston design of my cs-400 ? I understand the concept of the pop up piston taking up space in the Squish band.

What do the cutout portions on the pictured one do?

 

[Mad Professor]

Cutouts change port timing of transfers and direct flow

 

[Sloughfoot]

Stihl did this? Impressive if they did.

 

[hacskaroly]

Stihl did this?

CS-400....Echo

 

[Sloughfoot]

CS-400....Echo

That adds up. Can't see the Boxheads in Waiblingen having the innovation.

 

[tree monkey]

old school porting when you don't have the tools to raise the ports

 

[Jusgunn3]

Very interesting!

 

[huskihl]

Kinda farks with the squish band and squish velocity

 

[Ketchup]

Cheaper to modify existing pistons than cast jugs with higher transfers?

 

[two4spooky]

Wow, EPA emissions are getting wild here with two stroke chain saws. Old school models are looking better and better. Even the poor quality CN clones are starting to look appealing.

 

[STOVE]

old school porting when you don't have the tools to raise the ports

So theoretically could you modify them instead of the jug itself?

 

[EFSM]

So theoretically could you modify them instead of the jug itself?

Yes, although it will reduce compression

 

[Sloughfoot]

So theoretically could you modify them instead of the jug itself?

Pretty common to take a little off the bottom of the skirt on the intake side instead of lowering the port.

 

[STOVE]

Yes, although it will reduce compression

Pretty common to take a little off the bottom of the skirt on the intake side instead of lowering the port.

Thanks for the responses. Learn something everyday.

Is that a more common practice on clamshells? Due to difficulty getting inside the jug?

 

[Sloughfoot]

Thanks for the responses. Learn something everyday.

Is that a more common practice on clamshells? Due to difficulty getting inside the jug?

Not necessarily. Quick and easy on any type, might be less to lose modifying the piston instead of the cylinder. Or you might not want to alter the shape of the port. Problem with clamshells is it costs a million dollars to lower the cylinder to increase compression.

 

[STOVE]

Not necessarily. Quick and easy on any type, might be less to lose modifying the piston instead of the cylinder. Or you might not want to alter the shape of the port. Problem with clamshells is it costs a million dollars to lower the cylinder to increase compression.

That’s a lot of cheddar. I’m not looking to do anything to my clamshell cs-400. Just like to learn why things are the way they are.

 

[Motorka]

So theoretically could you modify them instead of the jug itself?

In old days they modded piston . It was cheaper if someting went wrong.... And piston was lighter ...

 

[edisto]

old school porting when you don't have the tools to raise the ports

It also can be a good way of dialing in timing with a cheap aftermarket piston before cutting on an expensive jug.

 

[DillonBuck]

Not necessarily. Quick and easy on any type, might be less to lose modifying the piston instead of the cylinder. Or you might not want to alter the shape of the port. Problem with clamshells is it costs a million dollars to lower the cylinder to increase compression.

Maybe not a million.
I did it on a Jonnypoulan for Dad.
.058 squish…. Spent a lot of hours gluing pvc onto EMT, then turning the mandrel(with machined in stops) to cut the pockets with emery cloth. Once it was all set up, it took 5 minutes to cut the pockets. Then had to cut the base to match. 022 squish now. A little grinding to help it push air out of the case, tickled and opened everything. Kept it mild, he tends to lean on a saw, didn’t want him to fry it. We are both happy. A 2036 became a pretty potent 2040 for $100. And more value in labor than two of them cost new.