The SCARR Husqvarna 592XP build thread.

[huskihl]

thank you thats what i figured was happening but i have a way of overthinking stuff sometimes

It makes more sense when you realize that cutting the band actually reduces the compression, but it allows you to cut the base and tighten squish to raise it back up

 

[Lee H]

I ran a buddy's stock like new jonsereds 90 that was 205# of compression. Torque monster for a stocker

I have a Jonsereds 80 with 225 psi. It is completely stock.

 

[pbillyi69]

i would really like to port some of my saws but i dont have the tools which doesnt mean that i cant have someone else make changes or send them out but where is the fun in that. it would get costly fast. making it cheaper to have someone else do the porting which would be fine and i have considered it. i like to tinker though

 

[huskyboy]

To an extent, when it comes to a 2 cycle engine. At some point, and it's a point that one would consider low, it starts to be counterproductive. The characteristics of these engines require a...freeness for a lack of a better term. Beyond 220psi for engines greater than 50ccs and *some* designs start to be less powerful or create excess heat. Beyond 70ccs I prefer to see them at 200 or less. Especially taking into consideration the starter design etc...now I'm rambling nonsense. Sorry guys.

Too much compression = heat. Heat soak = power loss after a couple long cuts. Heat is the enemy of a chainsaw when working it hard. When that point of too much compression is… probably depends on how good the particular model saw’s cooling system is and how effective it is at dissipating heat.

 

[Maintenance Chief]

Too much compression?
I think the bigger saws dissipate alot more heat off with more surface area. Design certainly would affect that.
I like a bump in compression and haven't found a limit yet? Maybe for a work saw, problems would be present ,but firewood duty amd a few mill runs I haven't run into problems.
I will say that my el'cheapo Ms441 build has a lot of compression and its been used hard and dropped a few big as$ trees with out heat issues.

 

[srcarr52]

No gauge will be more accurate than the math Shaun showed.

I do not recall the difference between his math and the first comp he took with gauge but after machine work Id hazard it will show the same % of difference.

The math has been within 5-10%. Single ring saws do read significantly lower than the theoretical.

 

[Dieselshawn]

It is true that more compression means more heat.

Good maintenance of cleaning the cooling fins goes a long way.

I haven’t seen many loggers really deep clean their saws yet. But I have myself.

The logging friends I have, I just recently explained to them that cleaning the fins and the whole saw goes a long way to extending saw life. Like not just blow the fins off with compressed air but like scrubbing the fins with degreaser and a brush.

I think a saw that’s running very hot from poor cooling also burns the oil differently which ends up cooking more and wearing the piston out faster with carbon packing around the rings.

 

[Funky sawman]

It is true that more compression means more heat.

Good maintenance of cleaning the cooling fins goes a long way.

I haven’t seen many loggers really deep clean their saws yet. But I have myself.

The logging friends I have, I just recently explained to them that cleaning the fins and the whole saw goes a long way to extending saw life. Like not just blow the fins off with compressed air but like scrubbing the fins with degreaser and a brush.

I think a saw that’s running very hot from poor cooling also burns the oil differently which ends up cooking more and wearing the piston out faster with carbon packing around the rings.

I take the sharp end of a round file and scrape my fins out once a week, I must be the only "logger" that maintains his money makers

 

[smokey7]

I dont think the fins need to be bare metal but not caked with packed dust is required. Semi frequent blow offs with the muffler off is all thats needed usually

 

[Maintenance Chief]

I cut firewood for 2 years with my ProMac10-10 and PM700 I frequently cleaned the cylinder, clutch ,and air filter/carb box.
I was absolutely blown away by the amount of saw cake under the recoil cover , so now those get taken off periodically.
Non Chlorinated brake clean and an air nozzle is the lazy mans way of getting the build up from the cylinder fins, I do that too.

 

[Stackowood]

Comparing the cylinder, again 585 on the left.

All the ports look of similar shape and size (ratio to bore). The transfer lowers are pretty much identical, of course the bores are different sizes but so are the skirt extensions. So the 585 skirt extension is floating around in the case. Both exhaust ports have an identical wave pattern in the roof. The 585 intake port is rough cast while the 592 port is smooth like it's been machined. You can see the stock squish measured at 0.023" and 0.022".

View attachment 317015 View attachment 317014 View attachment 317016 View attachment 317017

The transfer runners look similar to a 461. What is gained by having the runners mate with the case at the front of the cylinder instead of on the sides as usual?

 

[Sawrain]

The math has been within 5-10%. Single ring saws do read significantly lower than the theoretical.

Interesting, with well seated twin rings has the tested figure ever been higher than calculated?

Impressive to have it land right where you calculate.

No gauge will be more accurate than the math Shaun showed.

Many would, for closer mathematical accuracy you would need know the polytropic index of compression, a moving target depending especially on rpm & temperature.

And of course the previously mentioned ring sealing effectiveness is involved.

A pressure sensor that has little to no effect on clearance volume would still have the final say in my book.

 

[srcarr52]

Interesting, with well seated twin rings has the tested figure ever been higher than calculated?

Only if it's got a lot of assembly oil taking up some chamber volume.

 

[Stump Shot]

The transfer runners look similar to a 461. What is gained by having the runners mate with the case at the front of the cylinder instead of on the sides as usual?

I believe it's about cooling the cylinder at its hottest point, the exhaust port with the incoming fuel/air charge.

 

[srcarr52]

I was playing around with the 585 carb when I noticed both the 585 and 592 carbs have the high alcohol tolerant diaphragms. The pump side is also a clear membrane.

 

[Woodpecker]

I was playing around with the 585 carb when I noticed both the 585 and 592 carbs have the high alcohol tolerant diaphragms. The pump side is also a clear membrane.

Noice!

 

[species8472]

 

[qurotro]

Wow.. That's interesting. Almost forget that design. Heard that for a long time.

 

[pbillyi69]

if that new design is everything they say it is thats great.

 

[srcarr52]

Sorry guys, I know this is going very slow. I went to cut the squish and bases tonight but found the cylinders too large to bolt to my normal squish cutting plate so I had to make a new one. I'll also have to make a 53mm mandrel to cut the base of the 585, at least I have a 55mm one for the 592.