Husqvarna 365 special pop up

[farmguywithasaw]

So I had 3 48mm jugs laying around. I decided to do a “machining only” build as I have never tried machine work on a cylinder. It went well except for the fact with the new hyway pop up piston that I got the squish was terrible. With the base gasket it was .062”. Now with the base gasket it’s at 0.023. Initial compression is at 170 psi. Not sure where the numbers are as I planned not to do port work until after I try it. Haven’t cut any wood yet but seems snappy. Anyway my point is I don’t think those pop ups are worth it without machining. I think it would have lost compression over stock piston. Basically they take a stock flat top and machine 0.010” or so of the top to make the “pop up”

 

[ballisticdoughnut]

Gotta be careful with some of the pop up pistons. I’ve seen more than a few that were essentially stock (dimensionally) that simply had the crown cut to make the step if that makes sense. I will say from experience the Hyway pop up pistons for 266 are legit.

 

[farmguywithasaw]

Gotta be careful with some of the pop up pistons. I’ve seen more than a few that were essentially stock (dimensionally) that simply had the crown cut to make the pop up if that makes sense.

Yes that’s what I believe the one I put in was like. After decking the cylinder it’s irrelevant so a guy could make there own from a stock piston and 10 min in the lathe

 

[ballisticdoughnut]

Yes that’s what I believe the one I put in was like. After decking the cylinder it’s irrelevant so a guy could make there own from a stock piston and 10 min in the lathe

What brand position did you use?

 

[farmguywithasaw]

Hyway

https://www.hlsproparts.com/product-p/h31364.htm

 

[farmguywithasaw]

What brand position did you use?

 

[ballisticdoughnut]

Interesting. I’ve always been a little sus about aftermarket chainsaw parts and as a rule I don’t use them especially in customer equipment. I took a chance on the Hyway 266 pop up piston and to my surprise it was a legit pop up. Quality of the casting, machine work, etc really impressed me. Measured it against a NOS 266 “B” piston and it was bang on in every aspect. Sounds to me they haven’t done their homework on the 365 special pistons.

 

[farmguywithasaw]

Interesting. I’ve always been a little sus about aftermarket chainsaw parts and as a rule I don’t use them especially in customer equipment. I took a chance on the Hyway 266 pop up piston and to my surprise it was a legit pop up. Quality of the casting, machine work, etc really impressed me. Measured it against a NOS 266 “B” piston and it was bang on in every aspect. Sounds to me they haven’t done their homework on the 365 special pistons.

Yeah I have used some hyway stuff with success. But it’s always on my own stuff. I quit taking on peoples projects as I’m just too busy. The only failure I have had so far is a little red barn piston for my brush saw. The circlip **** out and by by top end. I definitely put it in correctly but I believe the clips might have been too big for the grove. Definitely have to pay attention to the am stuff closely

 

[old guy]

I bought two LRB pistons (popup) for 359, they were just stock with .020 cut from the edge, they were also .006 diff. from top of pin to the top of piston, I put one in & it made less power than stock, it's back in the box.

 

[Gord404]

I think popup pistons are a waist of time, was reading where they actualy disrupt the flow from the squish band to the center of piston.

 

[farmguywithasaw]

I think popup pistons are a waist of time, was reading where they actualy disrupt the flow from the squish band to the center of piston.

Are you talking during compression before the plug fires?

 

[ballisticdoughnut]

I think popup pistons are a waist of time, was reading where they actualy disrupt the flow from the squish band to the center of piston.

Higher compression equals more power. The Hyway 266 pop up piston has a .015 step which isn’t much but it’s something. Certainly not enough to disrupt “the squeeze” as piston approaches TDC. Stihl 028 super came with a pop up piston from the factory. Did they get it wrong?

 

[Gord404]

just what i was reading, I have used a couple but didn't find much in the way of gains, had a few Simonized saws come in and his crown was not too wide and I imagine most of his gains were through porting and squish plus flow .- he did real nice work

 

[serdie]

just what i was reading, I have used a couple but didn't find much in the way of gains, had a few Simonized saws come in and his crown was not too wide and I imagine most of his gains were through porting and squish plus flow .- he did real nice work

I have a LRB pop up in my 288 and my 372. They made a noticeable difference in large hard wood. Gotta keep an eye on their wrist pins in the past. The later ones are ok

 

[Chevboy0167]

I would like to see the flow pattern in a pop-up configuration as well as a "dish" style like some of the Husky 350 came with.

 

[Chevboy0167]

https://www.researchgate.net/publication/273301165_ANALYSIS_OF_PISTON_OF_TWO_STROKE_ENGINE

 

[sean donato]

That article is basically worthless to this topic of conversation. Large, slow speed engine of unknown port layout.