44mm Piston Dimentional Data Wanted - Stihl + Husky

[drf256]

An 026/260 base is only around .250-260 stock with the 260 being on the thicker side.

The 260 has a bigger chamber, which I prefer.

I'm still having an issue wrapping my head around piston compression height changing exhaust geometry on its own. A longer skirt allowing less Freeport I do see.

I see an opportunity for even more compression and even more out of the band.

 

[Brewz]

Piston height is the same (edit - by height I mean the pistons physical height, not its position in the cylinder)
Wrist pin is higher on the Husky pistons (288 v 660)

If you mount a 288 piston in a stock 660 cylinder you will have about .090 of squish.
The entire piston is the same height, it has just been moved down about .050 when mounted on the rod.

that is the geometry change.

 

[Brewz]

You then need to move the entire cylinder down to match it, which gives you awesome exhaust port timings

Take a small amount from the squish and you have a super low jug with lower compression because you have removed minimal from your squish band.

You need to forget the usual thinking around just lowering the cylinder.
The theory is to lower the piston and the cylinder by using a Husky piston in a Stihl cylinder.

This is all assuming the 246 piston crown sits lower when bolted on an 026 rod

 

[drf256]

I hope the ring stays above the intake roof at BDC.

Any change in these piston ported motors affects 20 other things.

For the price, it's worth the experiment.

If you're just dropping the jug, and not cutting the chamber, you're not gonna get much compression.

 

[Brewz]

na, I plan to cut squish too

I was going to contact you for advice

 

[Brewz]

It is so difficult to put this theory into text
I have it in my head

I dont have a lathe

Ahhhhhhhhhhhhhhhhhhhhh

I cant afford one either

 

[Brewz]

I bought one. For $27 shipped, I can be a sport.

Will cost me a bit over $50
I have ordered a 288 piston for my 066 as well while they are on sale.
I messaged D Dave about one but have not heard back yet

Imagine everything you do with chainsaws and double the price, or more.

Welcome to Australia
I need to chase every $ saving I can find

 

[drf256]

Look at this program

http://torqsoft.net/piston-position.html

A different comp height will affect other areas, but I tend to doubt it will effect ex roof height on its own.

When you make a popup piston, you cut the perimeter of the piston crown only. Then you drop the jug on it

The exhaust roof height stays the same.

 

[drf256]

Will cost me a bit over $50
I have ordered a 288 piston for my 066 as well while they are on sale.
I messaged D Dave about one but have not heard back yet

Imagine everything you do with chainsaws and double the price, or more.

Welcome to Australia
I need to chase every $ saving I can find

If you can wait 2 weeks, I'll let you know how the 246 piston works out. It may be a throwaway item.

But, @Red97 , it may be able to fit an Echo 490? The Windows will help at BDC, but I bet the skirts won't be wide enough.

 

[Brewz]

All good mate
I was ordering the 288 piston and 13mm bearing anyway and postage was the same with the 246 piston thrown in

I have high hopes

 

[awol]

I wish I could help you out guys, but the 246 piston is in my 3 cube saw, and we have a race tomorrow!
I do remember that the crown height was lower than on the 026, as I had to drop the jug .040" when going from the 026 to 246. I did do some machining to both of the pistons though, I just don't remember how much. Oh, and the 246 has longer skirts, as it elminated the free porting problem I was having with the 026.

 

[drf256]

I'm going to redo my 024/6 soon. I will futz wth this Pistons geometry a bit.

I'm already at a base of .206 IIRC.

Dropping it another .040 ain't working on this saw.

Sorry Mate. I just don't see the same thing you do on this one.

I am gonna try to 700* aluminum braze the exhaust roof on an AM jug.

 

[Brewz]

Good enough info for me!

Thanks awol.......... I was hoping on a .030 to .040 lower piston crown which will lower skirts

 

[Brewz]

If this piston works out as planned, I predict 100+* exhaust port timings with under 200 psi
It should achieve exactly the same result as a 288 piston in an 066/660, power through timing, not compression.

 

[Gentleman]

@Gentleman

Would you be able to pull one of these 246 pistons out of a box and get some measurements with a set of verniers?

Sure. What do you need measured?

 

[drf256]

If this piston works out as planned, I predict 100+* exhaust port timings with under 200 psi
It should achieve exactly the same result as a 288 piston in an 066/660, power through timing, not compression.

It's always through compression. You're just increasing the dynamic compression by changing the timing.

 

[drf256]

If this piston works out as planned, I predict 100+* exhaust port timings with under 200 psi
It should achieve exactly the same result as a 288 piston in an 066/660, power through timing, not compression.

Would be awesome if you can achieve this.

 

[Red97]

If you can wait 2 weeks, I'll let you know how the 246 piston works out. It may be a throwaway item.

But, @Red97 , it may be able to fit an Echo 490? The Windows will help at BDC, but I bet the skirts won't be wide enough.

I think a 44mm notched piston would be better. Need to find out what the rod bore diameter is. Ill be willing to bet it is the same as the 590, being they both have 11mm pins.

Not sure how well a window piston works in a bottom feeder??

I wish I could help you out guys, but the 246 piston is in my 3 cube saw, and we have a race tomorrow!
I do remember that the crown height was lower than on the 026, as I had to drop the jug .040" when going from the 026 to 246. I did do some machining to both of the pistons though, I just don't remember how much. Oh, and the 246 has longer skirts, as it elminated the free porting problem I was having with the 026.

Regarding my post above, have you tried a windowed piston in a bottom fed transfer saw?

 

[Brewz]

Sure. What do you need measured?

Na... all good now.... we have bought pistons to try anyway.

If you feel like throwing in extras for contributing forum members, like a Meteor cylinder to play with, feel free

 

[Brewz]

@drf255
I just pulled my 026 to bits to do some measuring.
95
118
70

What intake numbers are you finding work best on the 026?

Lowering the jug to fit the 246 piston will drop my exhaust into the 100's and bring my Intake floor down to mid 70's

Will these numbers work ok?