Let's Discuss 2100XP Pistons

[Mastermind]

Here's some pics of a project I'm currently tinkering on......



This is a KS 2100XP full skirt piston.



And a KS windowed version.

In this configuration, the designers added more intake timing, and lowered case compression.

Does anyone know which piston is the earlier design?



Now a Golf full skirt piston. It closely matches the KS slug.



Pin to crown height on the full skirt KS piston.



And the windowed KS. Not much different......so I'd feel safe running either design.



And the Golf......



I think I'd prefer the full skirt design because I like to see a lot of primary compression.......

 

[Mastermind]

The Golf piston is a crappy casting...........it needs work to even fit on the rod.

 

[Mastermind]

The KS slugs.....

 

[Mastermind]

I'm building a 2100XP, and a 285 with a 2100 top end. Yep......they will be for sale.

 

[Trx250r180]

I take it Golf is only aftermarket piston choice ? No meteor ?

 

[Mastermind]

No Meteor.

Epistan made, or makes one for these saws........but they are no better or worse than Golf.

 

[Trx250r180]

The middle one looks kind of like a stihl piston .

 

[Mastermind]

It sure does......

I've tried the windowed pistons (272XP) in the 372 before.....it just kills that saw. I figure that the full skirt piston in the 2100 will perform better too.

 

[srcarr52]

I've built one with a 395 piston... it runs better than the one I did with an original 2100 thin ring piston. You have to take a lot off the base to get the 395 piston to work, and the intake timing aproachs 160 without touching the port. A 394 piston has a little longer skirt, but the ring locating pins are not as ideal.

 

[Mastermind]

I've done quite a few of them. I'll be trying a few different things on these two.

 

[srcarr52]

I've done quite a few of them. I'll be trying a few different things on these two.

My choice of the three would be the full windowed KS. I bet if you measured the volume below the ring lands of both KS pistons they wouldn't be far enough off to make a significant difference in case compression.

 

[Mastermind]

The band at the bottom of the piston begs to differ........it would seal pretty well against the bore.

 

[srcarr52]

The band at the bottom of the piston begs to differ........it would seal pretty well against the bore.

That area on the other side of the of the full skirt is still considered crankcase area... just like the transfer ports.

Also when the piston is sealing the bore, it's forcing all the transfer flow through the piston. Which is smaller than the port, so the transfer flow has to speed up through the piston contraction and then enters the transfer port and outside of the piston where it's allowed to expand, velocity decreases creating all sorts of eddies and vortices which will be detrimental to the loop scavenging effect once in the cylinder.

 

[Mastermind]

You might be spot on Shawn. I've been really looking at this thing. I see a few things I can do to improve transfer flow and keep the full skirt piston. We shall see.......

 

[nenicu]

The EHP ported Redmax 5000 uses a piston similar to the last one [open bottom].The saw has a quad port jug with inside openigs[not from the bottom]. Husqvarna 372 has a bottom feed jug. The 2100 jug feeds from inside too. Maybe a talk with EHP is gonna make you decide what is the best option.

 

[srcarr52]

You might be spot on Shawn. I've been really looking at this thing. I see a few things I can do to improve transfer flow and keep the full skirt piston. We shall see.......

I put a lot of thought into the piston choice when I was building the last 2100. There are trade offs with each but one major thing I noticed was, what saw manufactures are using today as opposed to, in the past. Husqvarna originally had a full skirt large window piston in the 2100, 266, and 181 series. All have cylinder fed dual transfer ports and all except the 2100 eventually went to a windowed, partial skirt, skeleton type piston that we see a lot today. I can't think of one modern, large cc, cylinder feed transferred saw that doesn't have this style of piston. The 7900 first came with this piston but the latest design comes with a even skinner slab side without windows, which is going further away from the full skirt piston. Now, I'm not saying that the OEM's always get it right, but they are never that far off either.

 

[Modifiedmark]

I hope you have better luck with the golf piston then I did.

I put one straight out of the box in a 1100 saw. It didn't last long till it broke and the piston pin pulled the pin boss right out of the piston.

Just sayin..

 

[Mastermind]

I do have this.

 

[Marshy]

No Meteor.

Has anyone asked them if they would make some? I've done this with snowmobile pistons... Might be worth lookin into. Seems there is enough interest and saws out there.

 

[Mastermind]

I'm like Mark, scared of the Golf piston.

I've got a couple of used pistons that I'll be using.......or the 395XP piston.