MS660 Superstock

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Tzed250

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Some of you guys may not hit the other site so I thought I would get the info over here.


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.


<a href="http://www.flickr.com/photos/41385771@N03/5161655062/" title="insert by zweitakt250, on Flickr"><img src="http://farm2.static.flickr.com/1190/5161655062_45baef7094_b.jpg" width="820"height="655" alt="insert" /></a>



The saw was assembled with the Stihl cylinder and the squish measured. The squish varied across four corners between .021-.025".



The workstand helps.


<a href="http://www.flickr.com/photos/41385771@N03/5161057611/" title="chassis by zweitakt250, on Flickr"><img src="http://farm2.static.flickr.com/1206/5161057611_1c45f56374_b.jpg" width="820"height="544" alt="chassis" /></a>


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.

<a href="http://www.flickr.com/photos/41385771@N03/5161055573/" title="piston window right by zweitakt250, on Flickr"><img src="http://farm5.static.flickr.com/4062/5161055573_492178040f_b.jpg" width="820"height="655" alt="piston window right" /></a>


<a href="http://www.flickr.com/photos/41385771@N03/5161055065/" title="piston window left by zweitakt250, on Flickr"><img src="http://farm2.static.flickr.com/1315/5161055065_7779fe4a5a_b.jpg" width="820"height="655" alt="piston window left" /></a>




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.


<a href="http://www.flickr.com/photos/41385771@N03/5161657660/" title="intake 1 by zweitakt250, on Flickr"><img src="http://farm2.static.flickr.com/1405/5161657660_287bcd7a84_b.jpg" width="820"height="655" alt="intake 1" /></a>


<a href="http://www.flickr.com/photos/41385771@N03/5161053235/" title="intake 2 by zweitakt250, on Flickr"><img src="http://farm5.static.flickr.com/4002/5161053235_1bcb48bbca_b.jpg" width="820"height="655" alt="intake 2" /></a>



<a href="http://www.flickr.com/photos/41385771@N03/5161053675/" title="left upper 1 by zweitakt250, on Flickr"><img src="http://farm5.static.flickr.com/4066/5161053675_24bb9d08c0_b.jpg" width="820"height="655" alt="left upper 1" /></a>


<a href="http://www.flickr.com/photos/41385771@N03/5161657316/" title="exhaust 1 by zweitakt250, on Flickr"><img src="http://farm2.static.flickr.com/1384/5161657316_09bbb2caff_b.jpg" width="820"height="655" alt="exhaust 1" /></a>


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  • Thread Starter Thread Starter
  • #2
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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.

<a href="http://www.flickr.com/photos/41385771@N03/5161051549/" title="muffler 1 by zweitakt250, on

Flickr"><img src="http://farm5.static.flickr.com/4085/5161051549_fdcbd9ab08_b.jpg" width="820"height="655" alt="muffler 1" /></a>




<a href="http://www.flickr.com/photos/41385771@N03/5161653538/" title="muffler 2 by zweitakt250, on

Flickr"><img src="http://farm5.static.flickr.com/4131/5161653538_b941bf717d_b.jpg" width="820"height="544" alt="muffler 2" /></a>




After this set of mods the saw was run at the AS 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.


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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.




<a href="http://www.flickr.com/photos/41385771@N03/5161048015/" title="mandrel 2 by zweitakt250, on

Flickr"><img src="http://farm2.static.flickr.com/1047/5161048015_7891a4df7f_b.jpg" width="819"height="1024" alt="mandrel 2" /></a>




<a href="http://www.flickr.com/photos/41385771@N03/5161652336/" title="mandrel 1 by zweitakt250, on

Flickr"><img src="http://farm5.static.flickr.com/4086/5161652336_f600e51785_b.jpg" width="680"height="1024" alt="mandrel 1" /></a>




<a href="http://www.flickr.com/photos/41385771@N03/5161656020/" title="squish 1 by zweitakt250, on

Flickr"><img src="http://farm2.static.flickr.com/1095/5161656020_421ee6e112_b.jpg" width="820"height="544" alt="squish 1" /></a>






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.

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Thanks for looking.


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Cool documentation, the ports look real nice.

If you removed the gasket and turned down the base, it would seem that at least bringing the timing back up to stock would be a logical step.
 
  • Thread Starter Thread Starter
  • #7
I used the stock gasket. The base was cut .010" and the squish was cut .010" so the timing has not changed appreciably. I like to keep a gasket in place when possible.


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  • Thread Starter Thread Starter
  • #10
woodworkingboy said:
How did you get the reduced .019" squish? That isn't stock.
Click to expand...

The brass tacks of it all are that I removed slightly less than .01" from the squish band. The stock squish was from .021-.025"
 
Yah man that's sweet. I have a EHP modded 660 and love that saw, I'd really like to run one right opened up. Nice work.
 
  • Thread Starter Thread Starter
  • #15
squisher said:
Yah man that's sweet. I have a EHP modded 660 and love that saw, I'd really like to run one right opened up. Nice work.
Click to expand...

Thanks! I wish I had a big Dougie to sink it into!!!

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Thanks, that was a very tight stock squish, especially at the .021 area. It's what confused me. Closer to .030 is what I have always found on stock saws.
 
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  • #17
The newer 660s have very tight squish. My 660 would not even turn over if assembled without the base gasket. It makes it tough to find gains when there is no easy compression increase to be had.
 
Tzed250 said:
Thanks! I wish I had a big Dougie to sink it into!!!

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Click to expand...

Now thats something I always wondered. I see all these videos of guys cutting Douglas firs out west and up north. What wood do we have that cuts the similar around these parts WV Ohio Pa? White pine, Red pine, Spruces, Cottonwood, Yellow poplar, White poplar, etc?
 
I've never cut a tree out east. A softwood that hinges extremely well would be comparable. A very nice tree to work with.
 
I love the sound of a nicely done modded saw idling, like it is hot to trot. The dog at the end of the video going, "arf arf arf", seemed to approve too!
 
Tzed250 said:
I used the stock gasket. The base was cut .010" and the squish was cut .010" so the timing has not changed appreciably. I like to keep a gasket in place when possible.


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Click to expand...

First of all nice job .However as per the quote you said you cut 10 thou from the base and ground out about 10 from the perimeter of the combustion chamber if my interpretation of that statement is correct .

If you cut the base 10 thou you effectively lowered the exhaust opening by that much which would indeed make it a tad late with respect to stock timimg .Couple degrees more or less .By sanding or whatever on the perimeter of the combustion chamber you kind of lost the compression you should have gained .

I'm not trying to be a critic or a butt hole about this just pointing out facts .If you had domed or popped up that piston so as the dome entered the actual chamber instead of cutting down the edge of same with 19 thou clearance and good rings you should get higher comp readings than you indicate .
 
  • Thread Starter Thread Starter
  • #22
Al Smith said:
First of all nice job .However as per the quote you said you cut 10 thou from the base and ground out about 10 from the perimeter of the combustion chamber if my interpretation of that statement is correct .

If you cut the base 10 thou you effectively lowered the exhaust opening by that much which would indeed make it a tad late with respect to stock timimg .Couple degrees more or less .By sanding or whatever on the perimeter of the combustion chamber you kind of lost the compression you should have gained .

I'm not trying to be a critic or a butt hole about this just pointing out facts .If you had domed or popped up that piston so as the dome entered the actual chamber instead of cutting down the edge of same with 19 thou clearance and good rings you should get higher comp readings than you indicate .
Click to expand...

Hi Al,

If you look close at all of my info you will see more differences. One is the more shallow squish band angle. 7 deg. vs. 7.75. This yields less volume over the piston crown. Also, since the exhaust was lowered about .01" there is now more volume above the port edge. Since that larger volume is being compressed into a smaller volume (less squish, shallow squish band, ~.009 shorter combustion chamber) the static compression ratio is increased. The intake duration has changed the most. .01" lower, and the lip removed. Late 660s are notorious for excessive exhaust duration. I nipped that just a little. The saw won't stop here. It will see a pop up (my goal is north of 185psi), possible piston changes, more radical porting, and maybe even a two-piece head. Keep it tuned to this channel...


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Well like I said I think you are doing great ,it was just the figures or perhaps my misunderstanding of them that left me a little confused .

As for an 066.MS 660 or whatever ,I've had them apart for repairs but have never done any alterations so I don't know the exact particulars about them .It would be my assumption however regarding higher exhaust opening on the later models that same was done for more blowdown time and perhaps a few hundred RPM on the top end .

I've found in my own little experimentation that with higher comp readings that a few more degrees of blowdown combined with more transfer area has provided the more signigant gains as oppossed to longer exhaust .May not be the case in this case .

Keep on keepen on .:)
 
It's simple but complicated at the same time if that makes any sense .

You are dealing with an engine that uses loop porting theory and as such as the rpm's increase so do the size and perhaps shapes of the ports .Bigger isn't neccessarily better if done to extremes .

As the R's increase the time you have for intake,transfer and exhaust decrease so something has to altered in the scheme of things for the modifcation to work properly .

Some use known theories,some software to figure things out and in my case it's more or less a combo of written theory plus a semi educated guess .The guess BTW comes from first hand info from known builders .That said though ,as I've always maintained you don't actually know if your brainstorm will work until you try it out ---and so it goes ---:)
 
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