Author Topic: How does this piston mod work?  (Read 288 times)

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Offline joe_indi

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How does this piston mod work?
« on: August 10, 2023, 11:25:00 pm »
I tried this first on at least four FS55  trimmers, then on a after market MS460, yesterday on a MS180 and an old FS200 brushcutter.
My intention was to increase squish without touching the cylinder. Also ground about .3mm from exhaust port to advance the exhaust , opened muffler slightly to give less resistance.
Only issue was an oily exhaust deposit. But since I was using 25:1 fuel, I tried 50:1 which cleared out the exhaust.
The result of this mod was very quick throttle response and power output and the trimmers and brushcutters are hitting their speed limiter range very rapidly. On the 460 and 180 there is an increase rpm at WOT.
Since my mechanical skills are only practical not theoretical I wanted to know what was the reason.
And what I did was very crude (evident from the photo), since I just used a dremel

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Offline Cut4fun .

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Re: How does this piston mod work?
« Reply #1 on: August 11, 2023, 07:46:12 am »
Reasoning for wanting bigger squish was?  Just guessing due to gas octane quality there?

No clue on anything else beside making the piston lighter a bit.

Offline joe_indi

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Re: How does this piston mod work?
« Reply #2 on: December 14, 2023, 12:17:17 am »
Sorry for the delay in responding.
Over the past few months my browser kept popping up warnings when ever
I tried to access his forum as well as Forestry forum
To answer your query, yes, with E12 i was trying out various remedies for over heating and a knocking sound that sounded like
Piston slap or a worn con rod. But these went away when I increased squish on the piston.
About 0.3 mm . Tried on the lathe but this burring seems to increase the surface area more
And the engine runs smoother, though a bit ' throatier'
During my experiment i could afford a new piston if things turned wrong, cheaper than a cylinder.
After the initial positive effects i have done this for customers who brought in their brand new 382s and 462s for any precautionary work i could do to prevent breakdowns from fuel related issues , E fuel that is.
We will be going to E20 next year or in 2025
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Offline 3000 FPS

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Re: How does this piston mod work?
« Reply #3 on: December 14, 2023, 12:29:24 am »
Wow sorry to hear that about the E20.   That has to be hard on some of the older saws that were not designed for it.

Here I am making smaller squish on my saws, and you have to make the squish bigger.   

I think some of the old Poulan contervibes have a squish that is around 030".   I wonder how those would perform on E20.
PP 505, 475, 445.

 

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