A while back(a long while actually) I started making plans to mod my MS660. I decided I was going to do it
in stages, and try different approaches along the way. The saw had the 0603 Magnum muffler installed
before it ever saw wood. Knowing that port work was in the future, and wanting to keep the original
cylinder stock to have a backup, I started searching for MS660/066 top ends. I found a set of two
cylinders on eBay that had stripped spark plug threads. I took a chance and bought the parts. It turned
out great. The bores were in excellent condition and there was no damage. I really liked the deal because
one cylinder was a Stihl and the other a Mahle. I had $28.00 in two basically new cylinders. I bought a
plug thread repair kit from NAPA for $30.00 IIRC, and I fixed the Stihl cylinder plug threads.
The saw was assembled with the Stihl cylinder and the squish measured. The squish varied across four corners between .021-.025".
The workstand helps.
The first thing I did was clean up the piston. I removed all of the casting flash and then opened the
windows for better flow.
I then started on the cylinder, cleaning up all the ports. I widened the ports to the skirt limits, but I
did not change any timing, save for the intake duration which lengthens when you remove the silly lip in
the floor. The upper transfers were widened toward the intake side and the port roof cleaned up. The lower
transfers were lengthened, along with the cleanup. I prefer not to cut the lowers all the way to the base.
The exhaust was widened at the bore, made more square, and the exit size increased.