Minimum squish clearance test

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mweba

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Well the other day I sat down in front of AS and started reading. Gathering info on minimal squish and maximum compression. The general consensus for safe work saw squish is .020. I have two saws (80+cc) currently running .0175 with no issues and decided to find the limit. Test saw is a ms660. Started with the squish at .016 and ran it for a tank with not an issue. Tore her back down and repeated with the squish less every time. Granted there are many variables in measuring but did the best I could.

Any guess's how tight she got? Will say this, I had to slice my solder in half just to get the saw to turn over.
 
The problem is over time. With a squish too tight, I believe you can get erosion on the piston crown in the squish area. I find no need to go below .020, but that's just me. I can get 195psi on a 395 with .020, but also a popup.
 
Well the other day I sat down in front of AS and started reading. Gathering info on minimal squish and maximum compression. The general consensus for safe work saw squish is .020. I have two saws (80+cc) currently running .0175 with no issues and decided to find the limit. Test saw is a ms660. Started with the squish at .016 and ran it for a tank with not an issue. Tore her back down and repeated with the squish less every time. Granted there are many variables in measuring but did the best I could.

Any guess's how tight she got? Will say this, I had to slice my solder in half just to get the saw to turn over.

How tight is she?
 
Besides bumping into the roof of the chamber, squish also affects flame speed. I'm not up to speed on flame speed, but if I understand it right, tighter squish increases flame speed, which can lead to detonation.

I can't see pushing my luck for one or two extra psi.

Admittedly, some saws like the 066 need all the help they can get in the compression department.
 
The problem is over time. With a squish too tight, I believe you can get erosion on the piston crown in the squish area. I find no need to go below .020, but that's just me. I can get 195psi on a 395 with .020, but also a popup.

O I agree completely Will. It is more curiousity than anything. Also I just wanted to know how safe .020 was.

I'm gonna guess .010"
Dang close
 
Besides bumping into the roof of the chamber, squish also affects flame speed. I'm not up to speed on flame speed, but if I understand it right, tighter squish increases flame speed, which can lead to detonation.

I can't see pushing my luck for one or two extra psi.

Admittedly, some saws like the 066 need all the help they can get in the compression department.

Yep. Compression did not go up after .015. I believe running it hard would cause detonation. Had her up to 235ish

My 066 is .017" using a factory gasket. I'm guessing you're down to .012".

.017 is just right IMO. Nothing really to gain after that.
 
It's highly unlikely I'll ever go that far into modding my saw, but just for curiosity sake, how are you measuring the squish?

I assumed something like plasti-strip stuff for engine building?
 
Tap dancing

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This was .011 at 235+- compression
 
Yes I saw that, hence my post!

Ha ya figured you would catch it. Funny enough I almost didn't before shaving the jug again and getting ready to assemble it. That would have been BAD.
 
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