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.004˝ per inch. of bore is the standard but a little more is better than a little less when choosing.
You DID oil the parts up before assembly right?
I coat the piston/ring(s) with some fresh 2 stroke oil before I slide the jug on, looks like you were pulling through dry, metal to metal contact is the key to wear. When a 2 stroke is running, the oil is all over everything, creating a thin film that prevents metal from touching metal. It is only when this layer breaks down, or there is debris intrusion that wear occurs.
Let me ask you this. If you rebuilt your car engine, would you put the rods on dry, main bearings on dry, and slide the pistons into dry cylinders, then crank it for 15-20 seconds? Of course not. Same principle applies here.
Kenny I applaud you of your bravery w/no 2-stroke knowledge to get in there and grind on your cylinder. Port timings are very precise and need to be for a 2-stroke to perform well. When you lube your cylinder next time you assemble it, it may even bring your compression up. My bet is that your compression guage is off(fairly common in the world of cheap compression testers) especially seeing your compression reading when you only had a .008 squish. It is possible to have hogged out the ports enough to make your compression numbers lower substantially. But you said you just touched on them I believe...
+1 I'l rep ya too, shareing your learning experience as it was takes some balls.
There are a lot of details involved in moddifying an engine, and they are all important, sometimes for reasons that are not clearly evident from just looking at things.
It was mentioned earlier on squish that the clearance was needed for thermal expansion, I don't think this is realy 100% true. Only the portion of the piston from the rings up realy heats up and lengthens, and it's a very small amount, the rod is cooled by the charge so it should not be getting hot at all. On the other hand the jug heats up and lengthens so in reality I think squish clearances might be greater in a warm engine. And problems start long before there is physical contact betwean piston and head.
The issue of squish though is more complex, one aspect is that the rod of an engine is under tension as it comes towards TDC, in some cases there could be as much as 1000 pounds pulling up on the rod streaching it out. The other issue is in knowing the peak flame temperature in an engine can be over 2000f but yet aluminium melts at about 1200f, so then why does the heat of combustion not melt and burn away the surface of the piston? This is to do with boundry layers, there is a thin layer of fuel and air about .005 to .010 tick that does not burn during combustion and protects the piston and head from the heat of the flame front. If squish is run too tight this boundry layer is forced away allowing the combustion flame to directly contact the pistons and head surfaces heating them and literally boiling or burning away metal. I have seen this on an experimental saw I ran down to about .007, there were little craters and visible signs of errosion in the squish band. Once the boundry layer has been stripped away more heat will be directed into the piston crown heating it up over 500F this swells the piston crown and you risk seizing the saw up, but the killer is once the piston crown heads up over 500F it hits the auto ignition temp range of gasoline and starts to light up the charge in the squish area which makes for additional heating and a runaway situation.
Call this overthinking, say that you don't need to know this to build a saw and you may be right, but if you are interested in building a fast saw understanding some of these things and why to do or not do stuff helps goes a long way to wards avoiding problems. There is a fair be to good reading out there.
From the dammage on the piston and cyl, makes me question what are the chanfers or bevels on the port edges like? Got a phot of your port work?
I suspect his compression tester is also low reading and when coupled with his elevation can make for readings that can cause worry over nothing.
But whats bad is you will be planning your next saw before you know it!!!!!
LOL
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