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tommymacher
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tommymacher

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I was looking to bump the compression up a little on my play saw, is there any rule of thumb for how tight you can run the squish?
I've played around with snowmobiles and alot of guys will run the squish a little tighter the smaller the piston gets, but saws are a little smaller than I'm used to playing with.
I just don't want to set it up too tight and get myself into trouble.
 
timberwolf
timberwolf

timberwolf

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.020 min is safe in any saw I have done. 40cc to well over 120cc.

The tighter the squish the higher the squish velocity and the less wasted endgas. Getting the maximum squish velocity up over 25 m/s makes for good charge mixing and promotes fast and complete combustion. Tighter squish and higher RPM give higher squish velocty.
 
timberwolf
timberwolf

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1/16 inch soft electrical solder, just turn ignition off, pull the plug stick a stub of solder in against the cylinder wall and pull the saw over, then pull the stub of solder out and measure it. You should measure a few different places around the piston and may want to put in 2 pieces across from each other to take piston rocking out of the measurment.

Don't use solder over 1/16 of an inch or plumbers solder, it's too hard and won't give the best results not to mention stress on the saw needed to crush it. If you need to, lager diamiter solder can be pounded flat at the end and cut in half to reduce the amount of squishing the piston needs to do.
 
Last edited:
tommymacher
T

tommymacher

ArboristSite Lurker
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Messages
21
Location
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timberwolf said:
1/16 inch soft electrical solder, just turn ignition off, pull the plug stick a stub of solder in against the cylinder wall and pull the saw over, then pull the stub of solder out and measure it. You should measure a few different places around the piston and may want to put in 2 pieces across from each other to take piston rocking out of the measurment.

Don't use solder over 1/16 of an inch or plumbers solder, it's too hard and won't give the best results not to mention stress on the saw needed to crush it. If you need to, lager diamiter solder can be pounded flat at the end and cut in half to reduce the amount of squishing the piston needs to do.
Click to expand...

I was always tought too, to use two pieces at 180 deg apart and in line with the wrist pin to prevent the piston from rocking and give you a false read.
But that was with sleds that have a wee bit bigger cyl's.
Thanks a ton for the spec. though, I appreciate it.
 

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