Talk me off the edge of making a monster

[Backstage]

I have a 572xp in nearly new condition. It cranks to 150psi+, starts reliably, and cuts like crazy. I really should be satisfied right there. It’s more saw than I truly have a requirement for. End of story, right?

Then I see popup pistons are available for this model. It’s little red barn, not meteor. I bought one. It looks decent. Got the right size Caber rings.

Talk me out of cracking open a perfectly good saw that just started running right. Warrantee is not something I care about.

 

[ammoaddict]

If it were mine, I wouldn't do it.

Sent from my moto g(7) power using Tapatalk

 

[Bob Hedgecutter]

If you can afford to own the saw- it is yours to do with as you see fit.
Pretty simple "upgrade" to do and reversible if you decide it was not worth the $10 popup, or the Lil Red Flag piston lets go.... but that might cost you a new cylinder if it does.

 

[cookies]

throw that piston in the trash, if you want more oomph get it done right.

 

[Ronie]

I would do it and if squish wasn't to tight I'd delete the base gasket while I was at it.

 

[mbrick]

I would not put that piston in anything I own... mix some gas and cut with the 572!

 

[Backstage]

So I went and did it. I cracked Woody open and dropped in the LRB popup piston. Turns out, I’m the guy who has to touch the stove before believing it’s hot.

You have all failed me.

Compression before:


Compression After: WOW!


This is with deleting the base gasket while I was at it.

It starts HARD. Not just 180 compression hard to pull. It doesn’t want to fire. As in, starting it up is like waking up someone with a massive hangover who got in a barfight last night.

Once I fight it into starting, it idles poorly. Finally got it up and cutting, and it sounds like it’s going to explode and is producing excessive heat.

And this:


So I’ve gotten the original piston and base gasket back in and it’s back to running like the over enthusiastic homicidal kitten it was designed to be.

Detail inspected the crank and cylinder, and everything looks it came through. New pull on order.

This is not to say that the LRBpiston is anything but correctly made. It looks just fine.

Lessons learned:
1: This saw wasn’t designed to operate in this state. Maybe someone with more technical skill could make it do so, but…
2: I don’t have the technical skill to make this saw do this.
3: I’m basically the fat kid who managed to attract the prom queen’s attention. Probably best I just be deliriously happy and find some other hot stove to touch for now.

 

[user 122190]

Lots and lots of factory engineers put countless hours in designing and testing these saws before they are made available to the public. They are built to run long, run hard, and be usable by all potential buyers. It is a balance that makes or breaks a power saw for the companies reputation and profit. You want to monkey around with it -- Beware, you might just f'it up and bad.

Porting a saw is popular option on this site. Also available is to buy a more powerful and newer saw. Get a 500i if you are not getting enough thrills from your current saw. If you already have a 500i, take up parachuting or wingsuit flying.

This will put some lead in your pencil.



And if that isn't enough there is THIS (wingsuit flying *1000) -->

 

[Sierra_rider]

So I went and did it. I cracked Woody open and dropped in the LRB popup piston. Turns out, I’m the guy who has to touch the stove before believing it’s hot.

You have all failed me.

Compression before:
View attachment 1016839

Compression After: WOW!
View attachment 1016840

This is with deleting the base gasket while I was at it.

It starts HARD. Not just 180 compression hard to pull. It doesn’t want to fire. As in, starting it up is like waking up someone with a massive hangover who got in a barfight last night.

Once I fight it into starting, it idles poorly. Finally got it up and cutting, and it sounds like it’s going to explode and is producing excessive heat.

And this:
View attachment 1016841

So I’ve gotten the original piston and base gasket back in and it’s back to running like the over enthusiastic homicidal kitten it was designed to be.

Detail inspected the crank and cylinder, and everything looks it came through. New pull on order.

This is not to say that the LRBpiston is anything but correctly made. It looks just fine.

Lessons learned:
1: This saw wasn’t designed to operate in this state. Maybe someone with more technical skill could make it do so, but…
2: I don’t have the technical skill to make this saw do this.
3: I’m basically the fat kid who managed to attract the prom queen’s attention. Probably best I just be deliriously happy and find some other hot stove to touch for now.

I haven't messed with these pop-ups(not a fan,) is the material thicker in the center than a standard piston, or is it a milled down standard piston like guys were doing several years back. If it's the former, I could see why a base gasket delete and a pop up might be a bit much.

The other question, did you check your squish before and after all this? A base gasket is usually around .020", it's entirely possible that the squish was already close to optimum from the factory and the delete made it too tight.

I don't really use a compression gauge when I'm messing with saw cylinders. The reason being is that it doesn't tell the whole story...entirely possible to build a saw with a high-compression ratio that has a really small combustion chamber. However, it could have a tall exhaust port and only show so-so compression. The next saw I build, I'm going to machine a domed piston for it.

 

[Sierra_rider]

Lots and lots of factory engineers put countless hours in designing and testing these saws before they are made available to the public. They are built to run long, run hard, and be usable by all potential buyers. It is a balance that makes or breaks a power saw for the companies reputation and profit. You want to monkey around with it -- Beware, you might just f'it up and bad.

Porting a saw is popular option on this site. Also available is to buy a more powerful and newer saw. Get a 500i if you are not getting enough thrills from your current saw. If you already have a 500i, take up parachuting or wingsuit flying.

This will put some lead in your pencil.



And if that isn't enough there is THIS (wingsuit flying *1000) -->

Saw designs are usually a compromise, and gains can be made...some are better than others. When I do open up a saw, I sometimes wonder what the factory engineers were thinking. A perfect example of this is my 201tcm...looking at the factory numbers, it's no wonder why this saw gets so much flak. Ultra-wide squish band for the size and without much compression...then they just put in an ultra low exhaust port to try and give it torque. The problem is the saw had an incredibly lazy powerband.

A little bit of machine work, and a lot of grinding on the exhaust port...I can eat my cake and have it too. Retained and even improved the low-end torque, but that really woke that saw up...instant throttle response and pulls a higher rpm in the cut. Some saws are better, my 500i runs really good with just muffler mods. My 400 was pretty strong in stock form and the ports looked really nice...I like what I did with it, but it wasn't nearly the night/day difference that I've gotten out of some other saws.

 

[old guy]

So I went and did it. I cracked Woody open and dropped in the LRB popup piston. Turns out, I’m the guy who has to touch the stove before believing it’s hot.

You have all failed me.

Compression before:
View attachment 1016839

Compression After: WOW!
View attachment 1016840

This is with deleting the base gasket while I was at it.

It starts HARD. Not just 180 compression hard to pull. It doesn’t want to fire. As in, starting it up is like waking up someone with a massive hangover who got in a barfight last night.

Once I fight it into starting, it idles poorly. Finally got it up and cutting, and it sounds like it’s going to explode and is producing excessive heat.

And this:
View attachment 1016841

So I’ve gotten the original piston and base gasket back in and it’s back to running like the over enthusiastic homicidal kitten it was designed to be.

Detail inspected the crank and cylinder, and everything looks it came through. New pull on order.

This is not to say that the LRBpiston is anything but correctly made. It looks just fine.

Lessons learned:
1: This saw wasn’t designed to operate in this state. Maybe someone with more technical skill could make it do so, but…
2: I don’t have the technical skill to make this saw do this.
3: I’m basically the fat kid who managed to attract the prom queen’s attention. Probably best I just be deliriously happy and find some other hot stove to touch for now.

I bought 2 popup pistons from L R B for a 359, they only had .020 popups, they gave me no increase in comp.
One .006 difference from the pin hole to the top of the piston each side, the other was .004 difference, stock piston was .0005.
I have built a few saws with popups before with good success, but those L R B piston are trash.

 

[Maintenance supervisor]

The LRB pistons are known to have design flaws to the McCulloch crowd, and LRB has been aware of them, yet they do nothing but sell flawed pistons.

 

[camel2019]

Lots and lots of factory engineers put countless hours in designing and testing these saws before they are made available to the public. They are built to run long, run hard, and be usable by all potential buyers. It is a balance that makes or breaks a power saw for the companies reputation and profit. You want to monkey around with it -- Beware, you might just f'it up and bad.

Porting a saw is popular option on this site. Also available is to buy a more powerful and newer saw. Get a 500i if you are not getting enough thrills from your current saw. If you already have a 500i, take up parachuting or wingsuit flying.

This will put some lead in your pencil.

View attachment 1016856

And if that isn't enough there is THIS (wingsuit flying *1000) -->

View attachment 1016857

Lots of saws have some to be gained from modifications. From what I see from the big brands saws/equipment have a best before date for the most part now a days. restrictive mufflers and ports and some parts straight up made to fail over time most equipment owners would just toss and go buy new.

 

[HumBurner]

150psi seems a little low for a nearly new 572, no?

 

[Wombat Ranger]

Thanks for posting. Maybe you should have tried using the decomp button when starting.

 

[FlyingDutchman]

Built a Chinese big bore ms390 and did a little porting on it. I felt like it could have used a pop up. Didn't have stellar compression like a factory saw. Ran alright but just didn't have the huck i hoped, and that would have helped it. You can't do a base gasket delete on those.

I might do a pop-up on my next one, have a 290 with 100 psi compression on the bench, if I don't need to spring for bearings like the last one should be budget for it.

 

[ballisticdoughnut]

Husky 5 series are fairly high strung from the factory. They have hot start issues especially in hotter climates. Turning the wick up will only exacerbate existing “personally traits”.

 

[Backstage]

Thanks for posting. Maybe you should have tried using the decomp button when starting.

Um….yeah. I definitely tried that, thanks.

 

[Backstage]

Husky 5 series are fairly high strung from the factory. They have hot start issues especially in hotter climates. Turning the wick up will only exacerbate existing “personally traits”.

That's reduced or eliminated on the 572. It has this really cool space shuttle tile material baffle on the top cover that’s effective at thermally isolating the carb from the engine.

 

[Backstage]

150psi seems a little low for a nearly new 572, no?

Not by my gauge? This is an older 572 fwiw, but it reads exactly the same as a new one. Gauge/technique yields different results?