John Deere 66SV / Echo 610 Twin Cylinder

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"Model 66sv with18 in bar. Runs good. Chain needs sharpened. 125.00 alsohave a wood shark havent used in 2 years 14in bar no chain 50.00 ..." Straight from the original add. Copy/Paste
Right. He double the price when he got so much response. I never saw it at the lower price.
 
So ever since I've heard about this Kioritz twin, I've envisioned a parallel twin like the snowmobile engines they made in the 70s. An engine that fires a plug twice per revolution. As cool and as rare as this saw is, i have to admit that finding out that it is a boxer, is a big let down.
 
So, here's what I started with. I really should have gotten pics of the parts before cleaning. It was FILTHY!

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Here are all the parts all cleaned up.

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While I did not port the cylinders, I did de-carbon, de-burr, and polish them up. The combustion chambers and piston crowns were de-carboned as well. They went through the ultrasonic cleaner as well. The muffler gaskets were port matched. The carb went through the ultrasonic cleaner and got new diaphragms and gaskets. Believe it or not, the fuel lines were nice and supple. The muffler was wire brushed and painted. While temped to mod it a little, I did not. All I did was clean the spark arrestor screen. I put both cylinders on without gaskets and checked the squish. One was slightly over .020, while the other was only .015. I put a thin gasket under it and only used sealant on the other. I have not yet checked compression. One of the wires from the kill switch was totally severed, with no damage to the insulation. That took a while to find. I soldered it back together and sealed it with shrink tubing.
 
It's interesting those are two completely different cylinders as cast on the outside. At least the rear one took some factory machining for that corner clearance. Does the rear exhaust come out that port on the right of the handle or underneath?
 
Both exhaust ports exit straight down. The two cylinders are very different. The spark plug comes nearly straight out of the center on the rear. On the front, it comes out at nearly a right angle. Because of this, the combustion chambers are very different. As I expected, the compression on the rear cylinder is significantly higher, because of the pocket in the combustion chamber required to let it come out at such an angle.
 

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