Squish bands & Compression Overview of "Why" Simple Hop Up Concepts ANYONE Can Do To Chainsaws

Seems like I cover this once every few years, compression & efficiency along with squish bands and why it's worth getting to the .018 to .022 range on these little simplistic sub 100cc two strokes. I think the first time I covered this on video was in 2014 time frame. First time on the boards prolly around 2004. Problem was then I assumed everyone knew this so it was buried as incidental information in the video's of the time on something else. After watching some of the larger than my channel's attempts to cover things about making these things run better/different its apparent the basic physics of these little two strokes aren't really well understood and certainly not discussed. Not that is is my place to do that, but if I don't at least "kick" the bee's nest from time to time, it won't even be discussed and the freak show saws will dominate the conversation vs. good solid two stroke fundamentals. Funny to me is the history. Two strokes have been sorted out for decades. I doubt the power to weight ratio of the road racing Yamaha's from the 70's and 80's has really been improved on. Maybe with better materials pushing the edges of physics... Out board went one direction, snow mobiles another but the fundamentals are the same. Relative to saws.... Husqvarna as a company had pushed the performance of piston port single cylinder two strokes along with the rest of the Motocross manufacturers in the 60's thru 70's to the point of diminishing returns w/o things like water cooling, power valves to alter timing and even fuel injection. Not a surprise to me the Husqvarna EARLY on in the late 1960's entered the market with a light weight and powerful piston port design which is the genesis of MANY others spawned from the same research out of the major Swedish manufacturers of the time. Here in the States companies were selling heavy reed valve solution's while those Husqvarna's drove the marketplace to where every manufacturer has a similar layout. Always wondered how much of the Motorcycle RD team experience impacted the saw designs of the time. :) Any way going into the weeds. The "Tricks" and concepts I cover here were ones I learned back as a kid racing 125 motocross in the 1970's and as an engineer in the 1980's these same concepts were used to "tweak" my race bikes of the time. Of course they were WAY more advanced by then than ANY chainsaw build period. The cylinders looked like swiss cheese, pistons too as they squeezed more and wider power bands out of those little things. Eventually case reeds and water cooling with power valves won the day but who can forget the Piston Port KTM's Husqvarna's and Maico's of the late 70's :)

[@donnywalker4691]

That’s a good way to time transfers and if it didn’t work pistons are cheaper than wrecking a good cylinder eh good video

[@afleetcommand]

I think so as well. Actually was inspired by a fellow and company out your way years back to use that approach to "rough" out numbers.. :)

[@bmp0149]

Good way to test transfer and exhaust timing increases before grinding ports in cylinder.... does require new piston in the end though.

[@AndyH-13]

Thanks for sharing. This makes perfect sence and cheaper to recut a gasket if you stuff up than buying a new cylinder.

[@bryanhoy8785]

Thank you for being such a down to earth saw builder. It's so nice to have legit information. Love your channel.

[@IndianaDoug]

I’ve been seeing some great videos on these subjects recently, and this one is now exception. Freakin great stuff Walt👍🏻

[@alanreynolds2125]

That was a very very good video! makes a lot of sense even to an old bloke like me! thank you 👍👍👍

[@jamesconnors9388]

I recently bought an ebay junk 394 to build and the piston had one side filed down like that one you showed. You just explained why it was done. Thx walt good stuff as usual

[@jamesvieira8713]

Fantastic video Walter !

[@StuInTheSticks]

Pay attention children class is in session so take note's, don't know if Walt is the teacher we wish we all had or the mad scientist but one thing's for sure a lot of valuable info if you want to listen and learn. Once again a big thank you Walt for showing the rest of us your work take care.

[@fabzacres-blackcat]

Been using gaskets to adj squish and change intake/exhaust timing for years! It’s amazing how the engine “comes alive” when your MSV (max squish velocity) is correct(along with jetting , timing etc) . Nice thing about using gaskets is that they are inexpensive vs other more “permanent” methods. Once you remove metal it’s GONE forever , and unless you possess the ever elusive “put on tool” you could quickly find yourself SOL 😂

[@230e4]

Nice video Walt. I like how you did your 572 build. If one has the equipment and knowledge to crown the piston and machine the squish band to match fantastic! Being able to buy a $40 dollar pop-up piston, remove or replace the base gasket and do a muffler mod netting one a noticably better performing saw for all the reasons you mentioned is definitely a win. It really comes down to how much time and or money one wants to put into a saw and what the returns really are for that. Some may argue that modifying the piston causes a problem down the road when it comes time to replace it, perhaps for those not attune to such mods, but one can learn like most things, decide whether to duplicate going forward or make their own mod when the time comes to replace it. I find it interesting how alot of the porting and piston mods we see today are based off of what Stihl did to their saws in the 80's. I run saws with both the cost effective mods and full tilt custom machine work and definetly prefer both over stock for a production logging saw. My experience has been that they get the job done faster and more efficiently with a lighter saw which my body appreciates far greater than the cost. I have a Stihl 066 built by Madsons years ago that the only issue I have had with it was when it came time to replace the crank seals I discovered one of the nylon cages in one of the crank bearings was coming apart ;) Two of the dealers I buy new saws from offer new saws ported with a warranty. KZbin has been great for sharing this information, helping to educate folks, making saw mods more acceptable and giving them a basic understanding to decide what is best for their needs.

[@mattfleming86]

Oh boy. Thats twice today you hit me with something relevant to me.. I have been playing with a husky 51. Didn't have a way to raise transfers.. but I DID consider doing the piston top trick at one point. I have a good candidate piston (had one little score mark, now cleaned) to try it with :-D You're the best.

[@fabzacres-blackcat]

Gordon Jennings mentions these modifications to the piston in his book. I’ve used this trick many times with excellent results across many versions of saw both STIHL and Husqvarna. These 2-stroke engines were all worked out a loooooooong time ago , nothing new under the sun imho - however we do have some (an almost cult-like following I must add) that insist “their way” is the only way to build a saw - I assure you NOTHING could be further from the truth - this gent is showing you the straight-goods with no undue fanfare. You would be wise to listen to what he is telling you

[@timfunk5084]

Thanks very good explanation. Ready for the snow?

[@bmp0149]

Nice video, agree whole heartedly. Compression increase and setting the squish right gives me a nicer running saw with better response, just what you need for limbing. Bit more top end power too. And saw is more tolerant to mid throttle fueling issues which is a real bonus because we know these simple carbs dont always do the best job mid throttle even when set right at full throttle. One thing to think about - combustion starts with that spark at maybe 25 - 30 degrees btdc and goes on burning way past tdc when piston is no where near the squish band. How does that fit with the mental image of gas not burning in the squish band ? It doesnt. Tight squish is for turbulence primarily, which leads to better, faster combustion. Thats your efficiency gain.

[@fabzacres-blackcat]

Yes 👍… however you want the most force on the piston to occur around 15degrees ATDC for max power! This is a “moving target” and can really only be confirmed by the stopwatch or Dyno. Often overlooked is the fact the higher compression causes the combustion to occur SOONER so in effect you may find that retarding rather than advancing the spark will give the best power at the 9500-11000 rpm that these saws run in the wood

[@iraagans3144]

So I don't have a lathe and swapped out the piston in my G288XP and had to add a .080 gasket to keep it from being a head slapper. Basically raised all the ports and added a ton of compression, it runs alot better for me.

[@craigtimmons3468]

From .030 to .013 plus maybe a couple thousands once compressed with just a gasket is pretty good in my eyes. I just built another MS660 and with the stock metal gasket it was at .036 before compression, I cut a .010 gasket and after install and compression it's at .017 maybe a little tight but it's not a head slapper and runs like a rapped ape, LOL, but I'm not really sure how a rapped ape runs. I really only build work saws so the extra duration of being under pressure enhances my builds as I only try to clean up the transfers and ports and gasket matching to enhance and clean up the air flow.

[@clintdoucette2868]

Another great video! Appreciate the knowledge shared! Was wondering if you could explain a little on timing advance on saws on a video. I have a FT 372 I’ve done some mods on and wanted to try this

[@jerseyjoshua4818]

Mr. Brisco has been doing that to his pistons on his builds.

[@Rein_Ciarfella]

Do you do anything to increase airflow at the filter?

[@Mark_Tschetter]

Would these gaskets fit on a 372 x torque?

[@garengtutorial8923]

👍

[@Macgyver-ranch]

Have you used the Mrs's Cricut Maker for making gaskets or is that her next Xmas gift?

[@afleetcommand]

Actually bought one and never tried it. I BET that is a good approach. IF You have, put up a video please. And Please share also over at the FaceBook group "Husqvarna Autotunes Only "

[@Saw_Squatch]

I heard a rumour that husky is planning on changing the piston on the 562 to a dished piston, basically giving it the 261 treatment. What are your thoughts on this potential development?

[@afleetcommand]

It's true. Actually a document calls it an attempt to make them more "robust". Have to say it's an easy way to "take the heat" out. I think it is a marketing mistake as it will take the snap out of that saw.

[@Saw_Squatch]

@@afleetcommand yeah detuning the 562 seems like a really bad suit and tie decision

[@frankz1125]

I built a few now with motoseal for a gasket. Let it dry for 24 hrs. Seals very well and you get 25 + base gaskets from 1 tube. $8.99. Cheers

[@HanaBasara]

🙋🇷🇴👏

[@swsexton1829]

Who on eBay are you buying the gaskets from