Thread: MS660 Superstock

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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.























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The muffler was also further changed by removing the internal baffle box. The muffler is now virtually

identical to the ones fitted to early '90s 066s.











After this set of mods the saw was run at the WV GTG (Anybody interested in a wv GTG)at wvlogger's place. The saw ran fairly strong on its first tank of fuel, held

decent revs in the cut, and pulled the 8 pin OK with the 25" bar buried. When I arrived home I checked the

compression. It topped out at 167 psi.


The next step was to square the cylinder. I turned a mandrel from 2.375OD-1.5ID DOM tubing. The OD was set

to 2.125" which allowed a tight slip fit of the cylinder. The face of the mandrel was cut at a 7° angle,

.75° steeper than the 7.75° stock squish angle that I measured as best I could. This would allow me to

true the squish band and set a precise squish. I mounted the cylinder on the mandrel, then machined a

center in the top of the head. Once that was done I faced .010" from the base of the cylinder. This made

sure that the bore and base were perendicular to each other, though the stock runout was no more than

.001". Sorry for the blurry video, dirty iPhone lens.







After that was done, The work was removed from the lathe and a piece of self-adhesive sandpaper applied to

the face of the mandrel. A measurement was made from base to squish band, then the mandrel inserted in the

bore. Rotating the mandrel by hand allowed the squish band to be trued, and a precision squish to be set.

Unfortunately during this process I scratched the intake side of the liner with a diagonal score. I should

have cleaned the swarf out more often. The fact that I have less than $40.00 in the cylinder makes it hurt

a little less. I am not sure how much this has hurt the top end, but the saw is now making over 170 psi of

compression. Next, I reassembled the saw and checked the squish again. This time I measured .019" at all

four corners. This is the result I was looking for. Now the base, bore, crown, and squish band are all

square and true.





















for me it is running ok, but I know I have left plenty on the workbench. Not sure what I will do next, but

I'm sure something will pop up.





Thanks for looking.


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Not sure what I will do next, but I'm sure something will pop up.

What could You possibly mean by that?

Originally Posted by Steveo_supremo

What could You possibly mean by that?

well that clearly means he is planning on advancing the ignition....

how would one determine how and where to put the spark at? I searched for a minute, but the search function to me is like shooting in the dark. .

Originally Posted by 056 kid

how would one determine how and where to put the spark at? I searched for a minute, but the search function to me is like shooting in the dark. .

my understanding is that it is somewhat trial and error. You index the flywheel and advance a degree or two at a time and test it for improvement.

Looks like it's running good. So where's the popup, Mr. machinist?

Originally Posted by Zombiechopper

my understanding is that it is somewhat trial and error. You index the flywheel and advance a degree or two at a time and test it for improvement.

So it involves moving the flywheel like I was thinking. What does that involve? I was under the assumption that the flywheel is somewhat of a fixed deal,(key way). I feel that my 660 could benefit from some timing changes. Maybe Il pull up my old thread once I get some time to work on the saw if someone will help out. I know some are too big headed to help this "tool" LMAO.

Where did that talk about ignition timing come from?

Originally Posted by Tzed250

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That's already so bad you scared the #### out of someone's dog!

Originally Posted by blsnelling

Where did that talk about ignition timing come from?

Because he hinted that another modification would "pop up". That obviously means advanced ignition...

I know, I'm not funny. I'll shut up.

Originally Posted by 056 kid

So it involves moving the flywheel like I was thinking. What does that involve? I was under the assumption that the flywheel is somewhat of a fixed deal,(key way). I feel that my 660 could benefit from some timing changes. Maybe Il pull up my old thread once I get some time to work on the saw if someone will help out. I know some are too big headed to help this "tool" LMAO.

You remove the key and the taper holds it

Originally Posted by Zombiechopper

Because he hinted that another modification would "pop up". That obviously means advanced ignition...

I know, I'm not funny. I'll shut up.

I realized you said that tongue in cheek I guess not everyone else did, lol.

Originally Posted by Zombiechopper

You remove the key and the taper holds it

Interesting.

Originally Posted by 056 kid

Interesting.

same thing on industrial electric motors. The key is only to index it, the shaft taper and coresponding taper on the flywheel actually holds it. If the taper lossens the key will shear regardless, it doesn't have any strength to it really