Home owner MS170 Versus pro saw MS200 contest

[nimblebee]

Once the intake closes... the piston continues to descend, simultaneously compressing the crankcase gasses ... Anything you can do to get more ... from the block to the jug will make for more cylinder pressure and torque when the plug fires.  

Good information to know Mike! I've never considered modifying crankcase volume for increased power  :-)

This is why we play with the size, shape, layback angle and timing ...when the piston is trying to shove mix into the transfer leaving spots to hide reduces the quantity forced up.  

Satisfying to have your explanation of "why" behind increased power... I will need to look further into layback angle, as at this juncture, can't comprehend it's involvement ...

"leaving spots to hide" sounds familiar to the explanation of crowned pistons, where "leaving places to hide" results in unburned fuel...makes sense from that perspective.
Quote from: mike_belben on Wed Dec 30 2020 08:44:45 GMT-0600 (Central Standard Time)
"I have milled skirt windows in pistons to get the gas trapped under the pin to move over into the transfer port, with good results."

Mike, I have read of this concept before, and still have more learning to go to completely comprehend how and where best to apply this process on MS170 I'm learning on.

Quote from: mike_belben on Wed Dec 30 2020 08:44:45 GMT-0600 (Central Standard Time
Remember that combustion pressure is still high in the chamber and waiting to be exhausted.  when the transfer port opens higher pressure from the block helps the charge penetrate into the combustion space faster and more thoroughly.    Torque goes up.

I have certainly learned a lot through your posts Mike.  Thank you. That's one of the best things about being human: No one has to know everything. We can all learn from each other.  That works great!

Long as one can sort out the liars! ;-P ...  One of my favorite sayings: "Those who can, do.  Those who can't do, teach.  Those who can't teach, teach gym classes (Woody Allen).  Those who can't teach, preach. and Those who can't preach, are politicians"    :-D

[donbj]

A 2 stroke sucks through the carb and into the block while the piston is rising.  The high vacuum of the pistons syringe like movement will get the motion started and then the high inertia of the fuel/air mass at WOT will continue to ram mixture into the block even as the piston descends which should spit fuel out but does not.  The port floor and skirt length dictate at what crank degree the "intake valve" closes and ends the suction event.  
Once the intake closes... the piston continues to descend, simultaneously compressing the crankcase gasses [the first lump] and then revealing the top of the piston by unblocking the top of the transfer port.  Now the piston becomes a trash compactor of sorts.  It shoves the junk from one chamber to the other.  Anything you can do to get more junk from the block to the jug will make for more cylinder pressure and torque when the plug fires.  
This is why we play with the size, shape, layback angle and timing of transfer ports.  If your block has lots of casting cavities it can fit more mixture, true.  But when the piston is trying to shove mix into the transfer leaving spots to hide reduces the quantity forced up.
I have milled skirt windows in pistons to get the gas trapped under the pin to move over into the transfer port, with good results.  Remember syringes have flat bottoms. Hydraulic cylinders have flat faces. 4 stroke pistons have flat tops.  So a 2 stroke on the downstroke has a bunch of junk in the way of flow to the transfers
Filling in open corners and pockets with epoxy lowers the volume in the block which increases the compression ratio between block and combustion space.  Remember that combustion pressure is still high in the chamber and waiting to be exhausted.  when the transfer port opens higher pressure from the block helps the charge penetrate into the combustion space faster and more thoroughly.    Torque goes up.

Thanks for that Mike. I appreciate the time you took for that detail! Going to read that a couple more times to get more of it. I guess I should take an old cylinder and piston and note the ports as it travels up and down.
I never really did much wrenching on two stroke, just ran em. Picking up two pickup loads of chain saws I better get with the program! Thanks again.

[mike_belben]

Well, im a pretty good preacher too. 


Make the top of the transfers point the charge at the carb so it:

A. Pushes as much spent gas out the exhaust as possible

B. Doesnt blow fresh fuel right out the exhaust port during overlap. 

[mike_belben]

Youre welcome don.  Take one of the junk saws and cut the jug in half.  Also pull one side of the case and youll have your model.  



Whenever i do a saw i am porting the case and transfers together as one unit for flow quality, no ledges or lips left behind.  I will trade compression for laminar flow any day. 




  If theres anything turbulent and im feeling frisky enough to do all the work, it gets epoxied.  Devcon A2 with full paint removal, dimpling for tooth and usually drilling and pinning in tig filler rods for the epoxy to bond to if its a big chunk.  None has ever come off.  I did it in automotive intake ports and oil pumps for years.  And no i didnt learn it on youtube, i taught myself.  

[nimblebee]

I have milled skirt windows in pistons to get the gas trapped under the pin to move over into the transfer port, with good results.  

Mike, in a video series explaining porting by Scott Kunz, I've located an easy-to-comprehend (for me) explanation concerning removing some piston skirt, so as to create a "window" ... porting video series part 3, squish part 2 - YouTube ...  

This adds to my understanding of your post, about modifying piston and allowing gases passage from underneath piston ...

[mike_belben]

If i glue a dixie cup to your table and fill it withwater then say empty it, what would you do?


Drill holes in the sides. 


Picture it that way when looking at crankcase flow. The magic under the piston cant get over the wall created by the piston skirts, so help it get through them.  The transfer entrances are next to the pin, which isnt along the thrust axis.  Bottom of the skirts at north and south is critical but not east and west.  Im not saying a piston cant break but thats up to you to determine as the builder. 

[nimblebee]

...The magic under the piston cant get over the wall created by the piston skirts, so help it get through them.  The transfer entrances are next to the pin, which isnt along the thrust axis.  Bottom of the skirts at north and south is critical but not east and west.

Mike,

Researches into porting techniques has shown that there is definitely more than one way to get the job done, and my understanding is benefiting from seeing different methods and what results.

Your postings have been very helpful in pointing me to resources and ideas I never would have thought of, which helps to congeal understanding of the principles behind "why" modifications enhance performance.  

I'd say that's where the "magic" happens    ;-)

[nimblebee]

Don, 

Don't know if you've already made a "study model" from a junk saw as Mike's suggested? 

If it would be useful, here's video of cutaway model with accompanying explanations:

https://youtu.be/puKkc79kkww?t=25

[nimblebee]

Customizing my "B.S. 170+" chainsaw to best suit my particular purposes and preferences, I'm planning adding an additional top handle with throttle control.

I'm speculating that having two handles will give me the best of both worlds and the most utility out of my chainsaw?

What do you think about the utility of having a 2-handle saw?  Is adding top handle worth the bother?  I'm curious to know opinions.

[donbj]

Don,

Don't know if you've already made a "study model" from a junk saw as Mike's suggested?

If it would be useful, here's video of cutaway model with accompanying explanations:

https://youtu.be/puKkc79kkww?t=25

That's on the list for sure. Many thanks for the link! I watched a couple of that fellows videos. Very informative and straight forward. Helped alot.

[lxskllr]

Extra handles = extra weight. That eats into the big advantage of little saws. I think it might also throw the balance off in top handle use.

[nimblebee]

Extra handles = extra weight. That eats into the big advantage of little saws. I think it might also throw the balance off in top handle use.

All valid points you've brought up...  

Unclear concerning balance? ... top-handle for limbing, one-handed use... suppose I'd have to try & find out? ...  

keeping weight down, could form handle with larger sized PVC pipe... Once pipe's filled with hot sand & becomes pliable, one can bend/squash, pretty much (within reason) form whatever shape's needed ...  That's one method some utilize in forming frames for their DIY snow shoes ...  

Farmertec website has spare parts at ridiculously low prices; couple dollars gets trigger pieces for building secondary top handle ... Downside's ETA three weeks delivery, so most folk won't bother utilizing this resource...

To my way of thinking, tricky part's handle attachment... I've a few notions  along the lines of how to get there...

[sawguy21]

Saws are not designed to be used with one hand! If it kicks back you have no control. Be careful, we would rather talk to you not about you. I would not sell a top handle to a consumer.

[nimblebee]

Saws are not designed to be used with one hand! If it kicks back you have no control.

HHHHHHHhhhhhhhuuuuuuuuummmmmmmm...

Very good of you to bring that up! ...  I hadn't thought that far along ...  I know people limbing use saws (improperly) one handed...

I've concluded: necessary designing into handle a safety feature, such that in event saw kicks back, instantaneously brake's applied.  

One may not be able to prevent one-handed usage (there is that saying "You can't fix stupid"),  however, proposed safety feature would be equally  preventative with kickback as saw's chain brake is in two-handed use.

There's no getting around it: using a chainsaw is dangerous work; there is a limit to which preventive measures can prevail.

Many times I'm reminded, that the best "safety device" in preventing accidents sits underneath the hard hat.

[lxskllr]

Regarding balance... Dunno. That's something I'd have to feel to know. IMO, balance is king with a saw. I'd rather use a well balanced heavy saw, than a light one with bad balance. I'm also a little skeptical of homemade handles, both in comfort and longevity. Maybe a bar that connects to the front and rear handles? Would probably work, but then you're working around it in rear handle use. How to setup the trigger(s)?

Regarding one handing top handles... I think the safety aspect is a little nuanced. We all know why they were created, and it wasn't for two handed use. Two handed is better, but sometimes it isn't practical, and the safe approach is to use one hand. One should be cognizant of the increased risk, and take steps to counter it. The biggest danger is becoming blasé about it, and swinging it all over the place cause it's so easy to do. Sloppiness regardless of saw style will end up biting you.

[nimblebee]

...Maybe a bar that connects to the front and rear handles? Would probably work, but then you're working around it in rear handle use. How to setup the trigger(s)? ...

I've come along the same pathway in my thinking process concerning handle placement... needs to be sturdy; yet at the same time, out of the way for using original, rearmost handle.

Top handle also has to be detachable, so that you can open the top cover to change air filters and get at the guts of the saw.   The natural way to do that, would be to attach top handle onto top cover, but that won't work, because strength of top cover is insufficient to withstand loads handle would transfer to the top cover.

Natural conclusion would be that top handle itself would have to be attached, passing loads through the top cover getting strength/support by gripping something substantially strong underneath top cover at the rearmost of the top handle (near where the top cover has its attachment).

Top handle would need to grip at it's front, that bar which goes crosswise saw (doubtless someone will come along who knows proper terminology for this piece ), remain attached through top cover, and yet be strong enough while still removable with top cover.  Requires some interesting development work to be practical, eh? :-D

I apologize that conception is not easiest to describe and consequently picture in one's mind, but that's about the best I can manage. Perhaps it'd be best to illustrate with sketch of top handle concept I've in mind, posting with this description, thereby easing visualization of what's being considered? idk

I have some methods in mind to proceed along these lines, but it would take trial and error finding what worked best.  

One doubts it's the case for majority of people, but for me, this is a fun exercise, working/puzzling my way through to successful conclusion    :-)

Operating top handle's trigger would require internally operating rear handle's trigger at the same time, and as they would be linked, this would apply vice versa.  Interesting conundrums to resolve  :-)

[nimblebee]

Regarding balance... Dunno. That's something I'd have to feel to know. IMO, balance is king with a saw.

B.S.170+ ...I've been lucky trying approaches for DIY top handle so far... One of the things I've tried seems to be able to preserve balance and stay out of the way of the rear handle and the top cover removal... It looks like it will be doable  to run a linkage from top handle trigger down to bottom handle's throttle trigger ...  More work to go sorting it all out   :-)  Brad

[nimblebee]

Thought I would put in an update for folks following this thread as far as progress on the build.

I've purchased a shorter 14 inch bar (for 3/8 chain) to go on the chainsaw (came to me with a 16 inch bar), which is plenty enough for limbing.

3/8 inch chains and replacement 3/8 clutch drum chain sprocket,  with the idea of getting away from the Pico 3/8 chain and going to a beefier stronger more aggressive chain to  make best use of increased power porting will give B.S.170 +

Mostly I'm still studying porting threads by such gurus as Mastermind, Ironhorse, Tree monkey and others, sorting out which methods I wish to employ, and determining how far I want to take porting work.  There is a lot to  absorb with a steep learning curve, and a lot of differences in methodologies employed with the different builders :-)

Anticipating arrival of more tooling and parts; porting should go smoother with tungsten carbide bits.

[nimblebee]

Quick update for those following along this thread:

While I'm waiting for throttle trigger parts to ship in from China (for added 2nd top handle) and for eBay orders like tungsten carbide burr bits to arrive, I wanted to continue making progress with ;-) STILL (a) "B.S.170+" project, so I started constructing a toolbox case to hold chainsaw and accouterments.

Everywhere I looked online they wanted too much money for a chainsaw case but toolboxes were cheap, and sheaths fitting over bar were also quite affordable, so "badda bing, bada bang."  

Put the two together and you have a customized chainsaw carrying case to put your tools, bar and 2-cycle oil and whatever else all in one convenient location, in a lockable hard convenient plastic case.

Took my chainsaw without the bar and no oil or gas in it into different stores selling tool boxes, and I had no idea how many toolboxes would NOT fit my chainsaw properly.  

After the 4th store, I was starting to become frustrated, when at Home Depot found a Husky brand, 22-inch toolbox that fit my B.S.170+ chainsaw perfectly, with extra room left inside for various accouterments & tools AND top tray didn't even have to be cut to fit around my chainsaw handle!  :-)   We are happy now, with my purchase .

This really wasn't an original idea, because there's all kinds of DIY tutorials on "how to make a case for your chainsaw from a toolbox" if you want to look around online, but for me at least (being on a budget), this work-around makes for a good and practical solution.  

I have too many places for my money to go, to spend $50 to $80 on a chainsaw case, that really wouldn't do everything I wanted anyway.

Now all I have to do is find some Allis Chalmers orange paint, and I'll be able to have toolbox/bar sheath match high visibility clothing required at work.  

That'll make me look like I know what I'm doing, for all those "armchair experts," by having all colors matching    :-D   Beware: "straw-boss supervisors" are everywhere!    ;-P

DIY example: https://www.instructables.com/Toolbox-Into-Chainsaw-Case/

[nimblebee]

Brief update on B.S.170+, while waiting for ordered parts to arrive:

Having read on quite a few forums, unless you've a sharp blade, however powerful your saw, you don't have anything much impressive.

Taking this into consideration, I've ordered original Oregon PowerSharp starter kit, and for comparison, a Chinese knockoff sharpening cartridge, plus 5 chainsaw chains to experiment and modify/determining if something DIY works as well or better, via using a top-down sharpening profile.

With a three week lead time, some parts've arrived from FarmerTec and were installed, converting chainsaw bar to side adjustable & metal felling dogs installed, replacing ineffective OEM plastic dogs.

It didn't seem as though air filter on MS 170's was all that great a design,  so I have doubled up on my filtering by supplementing OEM with foam air filter.  

I'm speculating foam might restrict air flow, but loss's worthwhile, having superior filtration/keeping crud out of carburetor & preventing into engine.

Further investigating porting posts, watching guru's tutorials & reading  instructional forums  :-)