Talk me off the edge of making a monster

[Backstage]

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.

Yep, checked squish. So the LRB piston in my hands is exactly the same measurements as the original as far as I can tell. Only dimensional difference is that there's MORE material on the top. Takes up chamber space and increases compression.

My feeling is the same as yours, this saw is pretty close to optimum out of the box. Sometimes you can get told something by everyone. But you really don't know it until you try for yourself. Sometimes you even have fun doing it. That's really what this was all about.

 

[Woody912]

If it ain't broke don't fix it!

 

[serdie]

Yep, checked squish. So the LRB piston in my hands is exactly the same measurements as the original as far as I can tell. Only dimensional difference is that there's MORE material on the top. Takes up chamber space and increases compression.

My feeling is the same as yours, this saw is pretty close to optimum out of the box. Sometimes you can get told something by everyone. But you really don't know it until you try for yourself. Sometimes you even have fun doing it. That's really what this was all about.

I used LRB pop up in my ported 372 I DID not use the wrist pin or bearing, used oem it has made a noticeable difference in the bottom to mid range power. Not so much top end though. Been in for 2 years now still running strong. I won’t use these in my Macs though, they can fail

 

[northmanlogging]

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.

View attachment 950419

I'm late to the party, that said, I'm really surprised by all the folks saying don't do it.

DO IT!

Port the cylinder while your at it and maybe even cut the base for yet more compression (be careful though) port the exhaust, and remove any baffles.


Then when thats not enough monkey with the timing.

When you're all said and done you might have a fast saw and it will sound really bitchin. You might burn up a cylinder a little early, but you WILL have the experience of building a hot saw, and thats worth more then money.

 

[Backstage]

I'm late to the party, that said, I'm really surprised by all the folks saying don't do it.

DO IT!

Port the cylinder while your at it and maybe even cut the base for yet more compression (be careful though) port the exhaust, and remove any baffles.


Then when thats not enough monkey with the timing.

When you're all said and done you might have a fast saw and it will sound really bitchin. You might burn up a cylinder a little early, but you WILL have the experience of building a hot saw, and thats worth more then money.

One result of this experiment has been that for the 5xx series Huskies (or at least the 572), improving the saw requires more than just throwing in an “upgrade” part. I’ll keep it around at this point though. No sense in throwing it away or trying to ebay it.

But I‘m self aware enough to know I’m NOT up to doing timing or real porting work at this point.

Future me? Quite possible I’ll have that skill, and that piston will be in the 572 again and screaming. 10 years ago, I nearly trashed a saw because I didn’t know how to sharpen it. Or buy a new chain. So yeah…people do grow, and hope is real.

 

[northmanlogging]

One result of this experiment has been that for the 5xx series Huskies (or at least the 572), improving the saw requires more than just throwing in an “upgrade” part. I’ll keep it around at this point though. No sense in throwing it away or trying to ebay it.

But I‘m self aware enough to know I’m NOT up to doing timing or real porting work at this point.

Future me? Quite possible I’ll have that skill, and that piston will be in the 572 again and screaming. 10 years ago, I nearly trashed a saw because I didn’t know how to sharpen it. Or buy a new chain. So yeah…people do grow, and hope is real.

timing is fairly easy, just cut a little off the correct side of the woodruff key, reassemble forcing the flywheel the right way... worst case, you need a $1 woodruff key and start over. Monkeying with the cylinder height takes a good deal of care though, you absolutely need to check squish and clearances before you start, and it will change port timing as well, which is another thing to mess with...

 

[huskihl]

I don’t believe you can delete the base gasket on a 572 without squish being too tight. I’m guessing the popup piston was hitting the outer perimeter where the plating rolls onto the squish band

 

[Backstage]

I don’t believe you can delete the base gasket on a 572 without squish being too tight. I’m guessing the popup piston was hitting the outer perimeter where the plating rolls onto the squish band

You might be correct on that based on how it was running. It was my initial assumption during the brief runtime and the first thing I checked for was marking on the piston. The entire top surface looked unmarked save for the oil/carbon wash deposit.

 

[huskihl]

You might be correct on that based on how it was running. It was my initial assumption during the brief runtime and the first thing I checked for was marking on the piston. The entire top surface looked unmarked save for the oil/carbon wash deposit.

It’s hard to read with smashed solder. You’ll get heavy readings with thicker solder, as well. I use 1mm (.040”) rosin core and roll the flywheel back and forth about 10 times and then measure with calipers in several places on the solder

 

[user 122190]

If it ain't broke don't fix it!

Exactly. If you gots to fix something, get a project saw. Some POS abandoned in an alley dumpster, and go at it. For something in good working order, leave it be.

 

[Oldtoolsnewproblems]

i bet it might run nice again if you put the popup in there with the base gasket still installed... everyone needs .2 extra hp...

 

[Backstage]

i bet it might run nice again if you put the popup in there with the base gasket still installed... everyone needs .2 extra hp...

Get thee behind me, Tempter!

 

[HumBurner]

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?

Only saying that cause other saws I've comp. tested in that same cc range were 170-190 in used form. Being fully broken in, I would think higher than 150. Do you know if your saw is one of the first few runs of saws? There were some issues at the very beginning, but my.understanding is they quickly got worked out. Bearing/rod issues, if I recall.

 

[Sierra_rider]

Could just be the gauge, I've got a gauge that reads low.

 

[Lightning Performance]

It’s hard to read with smashed solder. You’ll get heavy readings with thicker solder, as well. I use 1mm (.040”) rosin core and roll the flywheel back and forth about 10 times and then measure with calipers in several places on the solder

And you know that can still be off 0.003 rhetorical really my bad.
He knows this already.
_______________________
If your not checking four points with clay and wet bearings in the motor it's never accurate. This quench area has to be whacked out and like Kev said possibly hitting the chamber or so close the pumping loss is brutal.

I'm surprised anyone would want more than 160 psi on a saw designed to be running less and still running a choked up muffler?
The carb will run lean in the mid range and tend to go leaner with more back pressure at WOT. Sounds like you almost cooked it with a thick cheap heavy piston. Better offerings have thinner lighter stronger pistons for a reason. They balance better and dissipate heat faster just like two compression rings vs one.

Take your popup and have that stupid lip feathered off and remove some muffler baffles while adding another exit port. Then you can file your piston some to gain intake or transfer port time. That thick block could use a diet plan. Then if your lucky it will run so good the piston will break off the skirt from high RPMs so enjoy it while it lasts.

Carbon buildup boost compression in well used engines with good ring seal.

 

[huskihl]

And you know that can still be off 0.003 rhetorical really my bad.
He knows this already.
_______________________
If your not checking four points with clay and wet bearings in the motor it's never accurate. This quench area has to be whacked out and like Kev said possibly hitting the chamber or so close the pumping loss is brutal.

I'm surprised anyone would want more than 160 psi on a saw designed to be running less and still running a choked up muffler?
The carb will run lean in the mid range and tend to go leaner with more back pressure at WOT. Sounds like you almost cooked it with a thick cheap heavy piston. Better offerings have thinner lighter stronger pistons for a reason. They balance better and dissipate heat faster just like two compression rings vs one.

Take your popup and have that stupid lip feathered off and remove some muffler baffles while adding another exit port. Then you can file your piston some to gain intake or transfer port time. That thick block could use a diet plan. Then if your lucky it will run so good the piston will break off the skirt from high RPMs so enjoy it while it lasts.

Carbon buildup boost compression in well used engines with good ring seal.

I’d bet I’m within .001” or 2. And I’m plenty good with that. It’s not a rocket

 

[Backstage]

Could just be the gauge, I've got a gauge that reads low.

I’m actually using a very precise Broke-My-Freakin-Recoil-calibrate-oTron compression meter.

 

[Lightning Performance]

I’d bet I’m within .001” or 2. And I’m plenty good with that. It’s not a rocket

So... you are building rockets now.

 

[Lightning Performance]

<profane post has been removed by moderation>

Oh my....
Corks, 20% bandaids with pedigrees on big asses. You need a farmers RPM multimeter with new muffler bearings.

Sounds serious but it's really not. Just get a bigger exit port.