Windowed piston in an open port cylinder ?

[Magic_Man]

Hello fellers, as a few of you have noticed I have been playing around with the Husqvarna 50/51/55 series. I was browsing the other day and found mention of a few guys putting an 028 super piston in a 46mm 55 cylinder. There is a video of one running on YouTube, seems to run ok. I'm just more curious as to the open transfer/windowed piston combination. What effects would it have over the standard full circle piston ?

 

[Stihlbro]

I think the 028 piston was used merely for the taller crown height, I maybe wrong.
There was a guy up north that did this, used a 50 special, 028 piston and the more current better filtration of the 55 air filter. Turned out to be a nice saw.

 

[Magic_Man]

My thought is that with the windowed piston the open transfers no longer have a "tunnel" that the full circle piston skirt was creating. But I also am just guessing, cause I'm still learning.

 

[Stihlbro]

I have tried both and honestly could not tell a difference.

 

[Magic_Man]

Interesting

 

[Stihlbro]

Well, let me clarify I had 44 and 45mm cylinders. I stuffed the transfers with epoxy to make a curve from the back wall to roof. Good experience. They just never performed like a closed port cylinder. Broke a few recoils by not using the decomp too.

 

[David Young]

028 s in a 55r jug makes a significant runner. Takes a little work but run well

Mostly because of the compression

 

[Magic_Man]

028 s in a 55r jug makes a significant runner. Takes a little work but run well

Mostly because of the compression

I'm gonna give it a try, any tips or recommendations ?

 

[David Young]

You have to open the pin boses a little and will need a base gasket spacer of 25-30 thou. Iirc. But depends on stock squish. Some of the early ones had huge squish and later on got much more realistic.

 

[David Young]

Also to what Joey said. Recoils are plastic. If you find a 55r jug with a decomp. Don't plug it

 

[Magic_Man]

Also to what Joey said. Recoils are plastic. If you find a 55r jug with a decomp. Don't plug it

The jug I have is cast for decomp but it hasn't been drilled and tapped.

 

[Stihlbro]

The jug I have is cast for decomp but it hasn't been drilled and tapped.

I would put one in.

 

[Basher]

028 s in a 55r jug makes a significant runner. Takes a little work but run well

Mostly because of the compression

Like 250 lbs.

 

[David Young]

I think that's I the realm of possibilities I think mine was 240 after a few cuts. I should dig that project out and continue some testing.

 

[Basher]

When I first posted about using the 028 piston I was ostracized, the world stopped turning and the earths poles lost magnetism.....LOL

 

[David Young]

When I first posted about using the 028 piston I was ostracized, the world stopped turning and the earths poles lost magnetism.....LOL

Well to be fair it is a pop up ..........

 

[Magic_Man]

Oh no, he said the p word, I think that's forbidden here... Lol

 

[Magic_Man]

You have to open the pin boses a little and will need a base gasket spacer of 25-30 thou. Iirc. But depends on stock squish. Some of the early ones had huge squish and later on got much more realistic.

So on the base gasket you say 25-30 thou. Is that to get squish where it needs to be or to bleed off compression. Would cutting the squish band on this combo take compression numbers over the top on this little saw ?

 

[David Young]

Just to get the squish to 18-22 thou range. It's pushing it now. It also keeps the numbers about stock.

 

[Magic_Man]

Makes sense, are you running stock timing numbers or did you change them ?