Another build thread - Farmertech MS660

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Rick Stephens

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I beg your forgiveness for starting another 660 build thread. I bought this box of parts during the members sale since it was so discounted. I really don't need another saw, Already have a couple 361s I am using to test various modification on. But you know how it is, CAD strikes where it will. At the time, I had a buddy who really wanted a 660 kit but at the last second bailed on our order. I figured he'd want it when it came in, but so far hasn't bit. I can't walk by the box any longer :p

I started out doing inspections, then assembled the cases to check squish and do some port planning. I had no intention of posting on the forums until I got surprised by, first, what seemed to be a better made cylinder than expectations. And second, by the squish I got. To go back one more step, when I opened the cylinder box they had packed the base gasket in with the cylinder and the gasket didn't survive the experience. I figured it wouldn't matter since in pretty much all my past Huztl builds the base gasket got deleted with squish being in the 40 thou range with a base gasket on every saw. Not this time. When I did a dry assembly without the base gasket the piston contacted the head. I installed the (worn through) base gasket and came up with between .018 and .020 measured all the way around. WTH - where'd a pleasant surprise come from on a kit saw? Much better manufacturing limits than I ever expected here.

The plating on this cylinder appears very consistent and heavier that I have seen in past builds. (I also did an MS250 back a while ago, and its cylinder was very well made and the plating was excellent - although other things were less precise on the MS250 manufacturing) The ports on this 660 are reasonably well done, but the edges are rough and sharp. I really wouldn't want to assemble this saw without cleaning up the ports at a minimum. I intend to do more than that with the ports and will need/want input from more experienced on increasing performance where justified. I want to open up a little, maybe add open finger ports for what looks to me to be a tiny upper transfer port. Suggestions more than welcome. Not looking to raise the power band. Maybe a misplaced goal, but seems if I am going to grind on it, might as well target reliable grunt power. Unlike the 361s where I am trying things like changing out carburetor and manifold to 440 parts, and getting progressively bigger ports, this saw needs to be a conservative target that I don't have to redo over and over again with the goal of reliable and not peak HP.

A couple starting place pics, comments suggestions welcome. Thanks for reading.

Rickdance.gif


exhaust1.jpg transfers1.jpg transfers2.jpg
 
I spoke a wee bit too soon. After doing my porting, I went to assemble this saw and found when the cylinder is compressed against an OEM Stihl base gasket that I had contact from piston to cylinder. I tried a bunch of things to find where and finally shoved a piece of carbon paper cut to piston diameter in and cranked it over a few times. Turns out the machining of the squish band didn't go out far enough and the piston was contacting between spark plug hole and squish. A little die grinder with a cutoff wheel and hopefully awe are rocking now.

clearance.jpg
 
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