Echo CS-620 or CS-621, which to buy

[Piston Skirt]

So what's a ventilated piston, you mentioned the 621 has one.

Exhaust, that's the first thing I dig into, gutted my little CS-352 a few weeks back,
straight after its first start just to make sure all was well.

here side by side 620/621

 

[Ford3000]

This man's chanel seems to show the 621 working very well.
Don't know what bar he is using, looks short.
Ok, he states he uses 37 & 45 cm bars, suits his style of cutting.

 

[Ford3000]

here side by side 620/621

Could that be described as a windowed piston, or
are they different again, Stihl and Husqvarna use them.
Seems a bad place to put two holes close to a very high
stress point in a piston. I see other pistons with these holes
below the piston pin where they do not get stressed as much.
The full force of the combustion pushing down on top of the
pin which in turn depends on a whole lot less metal now.

 

[Piston Skirt]

This man's chanel seems to show the 621 working very well.
Don't know what bar he is using, looks short.

Looks like box stock European 18” or 20” Sugi.

 

[Piston Skirt]

Could that be described as a windowed piston, or
are they different again, Stihl and Husqvarna use them.

Probably. This is nothing new generally, just a different approach for an updated engine.

 

[Ford3000]

Looks like box stock European 18” or 20” Sugi.

I thought it was an 18", you can hear the saw racing up
the revs as soon as he takes any weight off.

 

[Ford3000]

Any shots of inside the piston.
Do they still use the two thrust washers,
one either side of the top bearing.

 

[Piston Skirt]

Any shots of inside the piston.
Do they still use the two thrust washers,
one either side of the top bearing.

Here you go sir.
And yeah, I almost forgot - the ribs are thicker/stronger under piston head too.

 

[Ford3000]

Thank's for posting and explaining.
Does anyone know what the two ports in the piston
are for, what do they line up with, do they allow the mix
to get into the transfers early on, or is it stratified air that
they flow.

 

[Piston Skirt]

Thank's for posting and explaining.
Does anyone know what the two ports in the piston
are for, what do they line up with, do they allow the mix
to get into the transfers early on, or is it stratified air that
they flow.

It’s definitely nothing about stratified scavenging.
Cooling, enhancing cold mixture circulation around pin/bearing.

 

[Ford3000]

Anyone know how many drive links are used with the stock
18" bar on these 621 or 620 saws, I know its a 3/8 setup.

 

[Ford3000]

It’s definitely nothing about stratified scavenging.
Cooling, enhancing cold mixture circulation around pin/bearing.

Does that top bearing basically rock back and forth,
as opposed to the bearing in the bottom of the rod that
makes contact with the entire circumference of the crank
as it rotates, and thus it is the heat up top that is being addressed
with the ventilated piston design.
@Red97 , or anyone.

 

[Piston Skirt]

Anyone know how many drive links are used with the stock
18" bar on these 621 or 620 saws, I know its a 3/8 setup.

64 in non-US version

 

[Piston Skirt]

Does that top bearing basically rock back and forth,
as opposed to the bearing in the bottom of the rod that
makes contact with the entire circumference of the crank
as it rotates, and thus it is the heat up top that is being addressed
with the ventilated piston design.
@Red97 , or anyone.

The main issue is that the combustion heat travels towards the coldest point.
Cylinder walls cool down by transferring heat to the fins which are cooled by airflow.
Part of the piston heat travels partly through the oil film into the rings, then through the oil film into cylinder wall and so on.
The other part of the piston absorbed heat is cooled by fresh fuel mixture from under the piston.
And obviously the decent amount of the heat travels into pin->bearing->conrod.
That’s why overheated engines sometimes also tend to have subsequent upper bearing damage and upper conrod side discolouration.