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Old 10-29-2013, 10:34 PM   #1 (permalink)
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Default squish on stock 800

Wondering if anybody has checked the squish on a stock motor.

Just curious what it is.
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Old 10-30-2013, 07:21 AM   #2 (permalink)
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Grab some solder, a spark plug wrench and a set of calipers and let us know.




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Old 10-30-2013, 11:21 PM   #3 (permalink)
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Yea. I did. Just wondering if anybody else had checked thiers.

Thanks for letting me know just how easy it is tho.
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Old 10-30-2013, 11:57 PM   #4 (permalink)
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What did yours measure?
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Old 10-31-2013, 08:03 AM   #5 (permalink)
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.074". About. .020" too much. IMO.

Wondering if cutting head would cause detonation issues.
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Old 10-31-2013, 10:45 AM   #6 (permalink)
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Mind you that there are allot of variables that need to be taken into account when setting squish. Timing, Fuel, Pipe length, squish angle, piston dome shape, and port timing are all factors that have to work together for a completely effecient engine package. Squish is just about the lowest influence on it.

I have helped build allot of different 2-stroke engines and allot of big tripple Imp Stock sled engines, and have seen enignes with less than .01" squish and engines with .100" of squish. While it is an important area to adress, on a stock sled engine that is setup to run on pump gas with a factory exhaust on it, you really doing nothing more than emptying your wallet.

Now move to race gas, put a good pipe on it, and re-chamber the head (more angle with less squish) you can usually get more torque out of the motor and maybe a couple of HP, but you are also setting it up for less margin of error. This is a little safer on a engine with a DET sensosr, but it isnt a fail safe.

If you are wanting to deck the head, I would take the time to find the thickest jug gasket (either from the OEM or from Cometic) or look into a shim (Cometic can cut you a copper shim that matches a jug gasket), and deck the cylinders up about .05" (1.5mm) and then deck the head the same amout your raised the cylinders. This will increase port timing yet leave you with relatively the same runnign compression you had.
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Old 10-31-2013, 10:17 PM   #7 (permalink)
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.074" seems like a lot, almost so much that it doesn't seem reasonable. Sure the solder landed in the right spot? Its tough to see if the solder is right over the wrist pin and with the way these pistons rock, missing the location would change the number dramatically.
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Old 11-01-2013, 07:16 AM   #8 (permalink)
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It was in the right spot. I measured both cylinders, both sides of pistons.
I've done it many times before.

As far as the piston rock, my sled has RK-Tek direct replacement pistons. shouldn't be rocking very much.

That is why i wanted to know if anybody measured a stock motor.

I neglected to check mine before the pistons went in last season.

I realize there is a lot more at play than just the squish number, but as orville said, it seems rather loose.

I just wondered if this was what polaris did to protect themselves from detonation issues and crappy gas.

Curious what cutting .030" or so would do for it.
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Old 11-01-2013, 01:11 PM   #9 (permalink)
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Quote:
Originally Posted by ottawaair View Post

Curious what cutting .030" or so would do for it.
Performance wise, you would probably not even notice a difference. All you would do is make it more suseptable to detonation

But again, the squish angle (the angle between the top of the piston and the angle of the sqush bank on the head) has just as much to do with it as the "squish" itself

More squish angle (flatter pistons or a steeper angle of the head) will let you get away with less "squish". Pistons with more dome and shallower head angles will need more "squish"

This is the kind of thing that you can mess around with and you "might" gain enough power to actually tell the difference (if any), but take it .005" too far and you can run into detonation problems very quickly.

If the goal is to try and get some more power, this isn't the way to do it. Two Stroke compression is a completely different game that how tight the combustion chamber is to the piston. 60% of your compression comes from the pipe
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Old 11-01-2013, 01:29 PM   #10 (permalink)
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Dis you get the correct replacement pistons. I'm sure RKtec could tellyou what it should be.
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