Outback1
ArboristSite Member
If you are running a non - ported barrel is there any advantage to running a pop-up piston vs. a conventional piston.?
Pop-Up Piston vs. Conventional Piston
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A hair more compression in exchange for reduced swirl and cross flow from the transfers
Outback1
ArboristSite Member
Ok so does that equal to more torque?
I think a pop up gives a little more torque but the ones you buy have small pop ups so they don't give a huge compression bump. A pop up and a base gasket delete will give a nice increase in compression, lower your exhaust and increase your intake, that should give you some more torque.
Outback1
ArboristSite Member
Ok so if I don’t have a pop -up piston but delete the base gasket for the permatex one what would that do ? I measured the gasket that was on the saw and it was a .5 mm thick was that for more compression and torque as Stihl offers one that is 1 mm and the one that came on the saw that was .5 mm?
I use copy paper to make a base gasket that is then coated in copper coat for a thinner base gasket, it drops the cylinder down approx .3-.4 mm. It is more rigid than just silicone sealant and is much easier to re remove and clean up. It also gives a thickness that stays the same with 0 required drying time or fear of squished out material inside the engine. Using a thinner base gasket moves the cylinder down meaning the piston travels that much further into the bore generating more compression, it also moves the timing numbers about a degree per ten thousandth.
It should give you a little more torque, make sure you check your squish.
A pop up alone without dropping the base might increase compression, but it also raises the effective exhaust port height, which will can kill torque. Really it all depends on the motor. Some are helped some are hindered.
I don't like the idea of a pop up. They have the effect of making the top ring run hotter and they have the effect of making the squish less effective.
I don't like the idea of a pop up. They have the effect of making the top ring run hotter and they have the effect of making the squish less effective.
Before you delete the base gasket use a piece of solder to measure the "squish". Easy to do. Some cylinders come with tight squish and if you delete the base gasket the piston might hit the top of the cylinder (stihl 066 comes to mind) this can also happen with AM pistons that have the wrist pin location lower than stock . You probably want to determine why you need more power, sometimes a larger saw is better than a modified smaller saw. There is no substitute for cubic inches.
Outback1
ArboristSite Member
So what should the squish measurement be?
Generally about 0.020"... may want a bit more or less depending on the size of the saw.
What are you working on & what do you you plan on doing with it?
What are you working on & what do you you plan on doing with it?
The Shooters Apprentice
Addicted to ArboristSite
If the squish stays the same it won't change the timing. Most unless making a pop op from the existing piston, all the ones I've seen keep the top edge of the piston close to factory hight.
Outback1
ArboristSite Member
I’m rebuilding a 036 Pro that had a bad scored piston but the barrel I saved just waiting for all the part’s then back together. I polished up the exhaust port but left everything else alone . Barrel cleaned up beautifully. Traded a new 18” chain for the saw. I’ll use it cutting firewood as we have permission to clear 80 acre’s of wood! It will run with my MS461 & MS362MC. Probably put one of my 20” bars on it but have others as well 25”.
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What ever else you do make certain why the original top end burnt up and you've addressed that problem or the same thing is likely to happen again. My guess without further info is the pitiful, tiny flywheel side seal has failed...common on those. Vac/pressure test will tell the tale unless you already know what caused the first failure.
You'll definitely want to do a pressure/vacuum test before teardown to determine the cause of failure. If the unit is already apart closely inspect all rubber pieces or just replace (with OE if possible) all things rubber. FWIW a a dull chain can melt down a saw also, and a well sharpened is almost equivalent to porting your saw.
I'd say you came out a winner on that trade.
My suggestion would be to put the cylinder back on with your new piston & no gasket, measure squish & go from there.
As stated by others, check the rubber intake parts & seals over as best you can & DEFINITELY VAC/ PRESSURE TEST IT BEFORE YOU RUN IT
