Is this a source of those older "square" base 56mm kits?? or are these the same as those "junk" ones I had from another source...not liking the big chamfer taking sealing surface away in the pic though..
http://www.ebay.com/itm/New-56mm-Big-Bore-Cylinder-Piston-Assembly-kit-fit-for-Stihl-066-MS660-Chainsaw/172412802818?_trksid=p2047675.c100005.m1851&_trkparms=aid=2220071&algo=SIC.MBE&ao=2&asc=38530&meid=4c0877f87b594a70ad71be44f37a74f6&pid=100005&rk=6&rkt=6&sd=222357844246
I have seen at least five obvious different variants in these 56mm top ends now...

, really prefer the first ones I had got from Huztl 1.2, 2 years ago although just got one from Definitive Dave's store that is of the same casting style as the new Huztls, only everything is concentric. I Have to admit while the current batch from Huztl may not be as pretty, as demonstrated by "bling saw", they run just fine. I See the new "velocity" stack. Gen two has grooves to help hold the air filter it seems.
http://www.ebay.com/itm/Stihl-Chain...-Elf-Velocity-Stack-Made-in-USA-/322251934455
AND BTW the only way to see what I was concerned about with clutch drum run out is measuring from the bore axis for the bearing relative to outside diameter of the drum and splines for the sprocket. Thats whats critical anyway. If the bearing bore axis is either off center and axially out of alignment, the resultant "distance" change with crank rotation, the chain from a slightly loose to slightly tighter state every revolution...like mine did. I did notice...so I kept adjusting to make it work as I needed to cut & just grab a work saw as time is compressed. Figured...what the hell can't hurt much. Ran that for a while. Took a while and maybe it didn't matter. Maybe it did, either way last weekend the roller tip on the bar came apart. Granted bore cutting may have effected this and everything was icy and dirty. But that wobble couldn't have helped.
In retrospect, having that part concentric probably lessens the stress on both the bar and the main bearings...so maybe over analyzing...(who me??) but I am choosing to check each one now and or just go to a better option. I had a little tantrum and bought one from the local Stihl dealer..posted here with predictable results...lol, So.....how many of these builds have enough time on them to wear out a couple of chains? Thats a poll I would be interested in seeing. In my little set, the ones I personally use and the couple I have "lent" out there are 3 of the 4 I keep track of that not only have worn out a few chains, (Definition of worn out is filed to the point where you can't file or sharpen them anymore and they go to the scrap bin) but one has now blown up a bar tip...impatient operator error? or mechanical failure...that is the question. My answer....take away variables that common sense say my increase the chance of failure. Be interesting to hear for you folks as time goes on the experience and things that actually wear and/or fail in the actual service life over time. So far with mine the plastic get ugly unless plenty of pledge & elbow grease is applied and that rubber piece on top between the covers gets a hole worn in it, the decomps loose their plastic piece, and the sprockets wear pretty fast. But those saws make chips in a hurry!
Yet another little tib bit of information, I went back to a couple of the 660's to check the chain adjust...and the case castings on the ones I didn't have issues with had....predictably smaller slots. AND to add confusion, ONE of the earliest ones still had the AM adjuster and the SHAFT diameter was actually large to the point (Same dia as OEM) it didn't make sense to add either an OEM adjuster or a bushing on that saw. Then I had a run of threes where the AM adjusters failed immediately but OEM adjusters worked perfectly so there is and was no reason to add a bushing, this when I was putting together video's. So to this point in time only ONE of five actually needed a bushing. Of course it was this latest build and therefore representative of the current cases. I put a bushing anyway on the other "frequently used 56mm saw" that has a OEM adjuster and...its tighter but might be a solution to a problem it didn't have. SO like the clutch drums, and the cylinders, this is one of those deals where its possible you actually don't need to change things as these things are a constantly moving target, but if you do solutions are there and relatively easy. ME?? Once burned, twice shy. I just hard code into the next build the worst case lessons from the last. OEM adjuster, Better Clutch drum....AND a bushing in the adjuster if required. Looks to me a bushing might make the AM usable supported by a prior post here from someone who has done that. Save a few bucks?? why not. If it wears....then there always is OEM for better metal and if the case casting has those wider slots...a bushing.
What an AWESOME jigsaw puzzle these things are, don't you think so?? After the shop is built, hoping to try a "038" kit..

Looks to me like this "project" is in good hands...

Time to move on.