Zen and The Art of Chainsaw Modification

[timberwolf]

Where do all these port timing numbers come from? What about the angle of the transfers, polished ports vs textured, or intake resonance, indexed sparkplugs or otherwise just grinding away at the piston? Or the countless other ways to set up swirling motions in the intake, base and chamber?

It seems amongst the builders there is a great range of approaches ranging from; using guarded secret numbers and formulas handed down for generations, to quantum physics and super computers running real time 3d graphical simulations, to a "get to know your saw" then do what feels right, yet for other builders its more a story of a wonderful journey to find ones self, having relativly little to do with saw building.

So what do we really need to build saws, inner piece and enlightenment, supercomputers and an encyclopedia of formulas, or just the inside track on the magic numbers. Or is it just a lot of wrecked saws and a bit of this :bang: ?

Lots of people have posted the success stories of their porting work, but what about the rest of the cases, broken rings, jammed pistons, busted rods....

 

[Crofter]

I wonder if you were to take the jug off the saw and really get to know it, if it would start to commune with you and tell you what it needs to have its spirit freed. Perhaps sleep with the jug beside your head on the pilllow for a few nights! I don't believe all that technical stuff is necessary. You think sometimes things go wrong and we don't hear about it?

 

[Chainsaw Master]

First time I had the jug off my saw, was on a stump, way back in '76 or was it '77...anyway my only saw quit, a jonsred 621, a real silver beauty, with lotsa hump. Anyway there she was dead on the stump, so with allen wrench in hand, I pulled her jug off, right there in the middle of the woods. I ran to the saw shop, got a new piston, rings, and a head gasket. I was falling timber with that 621, an hour later!!!...... Life was never the same again.

 

[Husky nut]

First time I had the jug off my saw, was on a stump, way back in '76 or was it '77...anyway my only saw quit, a jonsred 621, a real silver beauty, with lotsa hump. Anyway there she was dead on the stump, so with allen wrench in hand, I pulled her jug off, right there in the middle of the woods. I ran to the saw shop, got a new piston, rings, and a head gasket. I was falling timber with that 621, an hour later!!!...... Life was never the same again.

How does this have anything to do with this post? Other then stating you can change your on cylinder and piston if need be...But lacks anything to do with modifying cylinders and pistons like in the main post...

 

[THALL10326]

First time I had the jug off my saw, was on a stump, way back in '76 or was it '77...anyway my only saw quit, a jonsred 621, a real silver beauty, with lotsa hump. Anyway there she was dead on the stump, so with allen wrench in hand, I pulled her jug off, right there in the middle of the woods. I ran to the saw shop, got a new piston, rings, and a head gasket. I was falling timber with that 621, an hour later!!!...... Life was never the same again.

Now thats what I call getting it done.................

 

[timberwolf]

Originally Posted by Chainsaw Master
First time I had the jug off my saw, was on a stump, way back in '76 or was it '77...anyway my only saw quit, a jonsred 621, a real silver beauty, with lotsa hump. Anyway there she was dead on the stump, so with allen wrench in hand, I pulled her jug off, right there in the middle of the woods. I ran to the saw shop, got a new piston, rings, and a head gasket. I was falling timber with that 621, an hour later!!!...... Life was never the same again.

Now thats what I call getting it done.................

Like I said, "...more a story of a wonderful journey to find ones self, having relativly little to do with saw building."

Great Nostalga moment from the 70's though. Get-er-done!

 

[rahtreelimbs]

I wonder if you were to take the jug off the saw and really get to know it, if it would start to commune with you and tell you what it needs to have its spirit freed. Perhaps sleep with the jug beside your head on the pilllow for a few nights! I don't believe all that technical stuff is necessary. You think sometimes things go wrong and we don't hear about it?

Frank, find the smallest cc chainsaw that you can for this application. Your rod ( I don't mean connecting rod ) will thank you!

 

[Chainsaw Master]

How does this have anything to do with this post? Other then stating you can change your on cylinder and piston if need be...But lacks anything to do with modifying cylinders and pistons like in the main post...

Everybody's gotta start somewhere

 

[rahtreelimbs]

Everybody's gotta start somewhere

True! Every builder learns something somewhere and goes from there adding their own element into it!

Some who have an understanding of the inner workings of the two stroke engine take this to a different/better/higher level.

Some don't have a clue as to what is going on and things go downhill.

Someones "dumb question" may be the biggest asset they have!

 

[timberwolf]

"getting to know my saw"

Did a little work on getting to know my saw. It's a bit long and if your not interested in fuel and engine efficiency and race chain vs round, you may want to head off to Hells Kitchen instead.

Date Jan 30

Temp -5C RH 95%

Husky 359 Stock stock Etech Muffler

Fuel 93 super 32:1 synthetic

Fuel Consumption

Objective 1: to measure fuel consumption at Idle, WO no load and WO full load.

Objective 2: to compare fuel consumption and cut times between comparable factory round ground and modified square filed chain and to compare the square inches of wood cut per unit time and unit fuel.

Method 1:

Idle: saw place on level filled to capacity and idled for 5 min with RPM monitored, then saw refilled with measured quantity of fuel, fuel temperature checked before and after to ensure volumetric thermal expansion does not influence measurements.

WO throttle no load: Saw filled to capacity and cycled through 6 cycles 10 seconds WO, 10 sec idle with RPM monitored, fuel measurement taken with same method and WO no load component will be determined by subtracting idle consumption from the total measured consumption.

WO throttle full load: three 3 cut sequences will be timed and fuel consumption measured with the same refill method. Wood 13 inch poplar.

Method 2:

Chains exchanged and WO throttle full load test repeated.

Findings:

Idle consumption:

5min idle measured at @3200 RPM ranging +/- 100 RPM
Fuel consumption 19 ml
Fuel temp constant -4 before and after

= 3.8 ml/min
= 1.2 ml per 1000 rotations (EDITED FROM 0.8)

WO throttle no load consumption:

1 min total idle @3200 RPM and 1 min total WO throttle @ 13,900 RPM
Fuel temp constant -4 before and after
Total fuel consumed =51 ml
Fuel consumed at WO throttle =51 ml - 4 ml = 47 ml

= 47 ml/min
= 3.4 ml per 1000 rotations

WO throttle full load consumption (factory chain):

9 total cuts average RPM 10,500 +/- 500 RPM tried to keep it close as possible but ranged between 10,000 and 11,000 RPM through the cuts.
Fuel temp constant -4 before and after

Total cut time 102 sec fuel consumption 60 ml
Best cut = 9.31 sec

= 35.3 ml/min
= 3.4 ml per 1000 rotations

Square inches of wood = 9 x 6.5^2 x pi = 1247 square inches

Best cut square inches per sec = 14.88 sqr in/sec
Average Fuel consumption ml per 100 sqr inches = 4.81 ml/100sqr in

WO throttle full load consumption (modified square filed):

9 total cuts average RPM 10,250 +/- 750 RPM tried to keep it close as possible to 10,500 but ranged between 9,500 and 11,000 RPM through the cuts. A bit more aggressive chain.

Total cut time 73 sec fuel consumption 45 ml
Best cut = 6.07 sec

= 37.0 ml/min
=3.6 ml per 1000 rotations

Square inches of wood = 9 x 6.5^2 x pi = 1247 square inches

Best cut square inches per sec = 22.83 sqr in/sec
Average Fuel consumption ml per 100 sqr inches = 3.61 ml/100sqr in

Conclusions:

Square filed race chain (sort of) was 39% faster in the test which translated into a fuel savings of 33%, Logically the if the chain cut 39 % faster a 39% fuel savings would be expected, however, the saw was loaded a bit more on the square filed chain, and more importantly the proportion of time the saw was at no load increased as the changeover time became a greater component of the total time with the faster chain. This might explain the higher than expected fuel consumption as unloaded full RPM demonstrated the highest fuel consumption per min. I need to back over the videos and see what ratio of cut time to changeover time was between the factory chain and modified chain.

Other Observations, idle fuel consumption is much better than what I measured on stihl 260 and 066 (but I had done some mod work before I checked them), seems the 359 is good on gas, but what will hapen if I try to get more power out of the saw, sure it will use more fuel, but just how much, will efficiency increase or decrease?

 

[Mr.]

Nirvana may only be achieved with a modded saw, so Zen is the correct terminology.

Lots of theory books have helped me. I am not anyone compared to the real builders, but since the heading was Zen. I am Zen with my mods.

Fred

 

[Crofter]

A little bit of meditation is good before any undertaking. Looks like a good bit of work went into putting those figures together. That is a fairly good gain over factory round chisel. There would be a bit more work on the chain than just a new tooth square filed I think. Put that chain away for later reference.

 

[timberwolf]

I went back over the video, and about 3 seconds was spent in the 6 change overs for both tests, 3 seconds is 4% of the time for the race chain and 3% for the round. that does not add up to much when multiplied by the difference in fuel consumption between WOT loaded and unloaded.

Change overs were slow, but I was going for consistancy, no cutouts and even RPM. Think I will look at my change overs more closely, lots of time to be had there.

Ed or others, what do you figgure is a good changeover time from the time the bar comes out of the wood until it goes back in.

 

[timberwolf]

D teched the 359 E tech toninght, added another .61 square inchs to the muffler opening by puting opening in the front cover all the way back to the back chamber.

Retested the fuel consumption at idle:

Idle jumped 500 RPM so I turned back the stop and tweaked the LS to get about 3200.

Repeated the 5 min idle test, fuel consumption jumped to 32 ml.

That increased the idle fuel consumption to 6.4 ml/ min or 2 ml/1000 rotations.

Thats a 68% increase in Idle Fuel Consumption!

I will have to wait until tomorow evening to recheck the WO consumption and cut times.

 

[Jim Mesthene]

Forgive me if this is a stupid question, but I'm a 4 stroke expert with only a working knowledge of 2 strokes.
The running theme on this site is: Open up the muffler, then you'll have to richen up the carb.
In the case cited above, the muffler was opened up, presumably power increased (as evidenced by the idle increase), and fuel consumption went way up without readjusting the carb.
Sounds to me like, without backpressure, all the exhaust was expelled and a fair amount of fresh mixture went out the port with it. That's OK, who cares about gas mileage on a chain saw.
With that much extra fuel used by just opening the muffler, why do you have to richen the mixture after mods? Sounds like it richened itself.
A muffler mod should make the saw pump more air, but why should it change the mixture provided by the carb?
Is the answer that when cooling the head by reducing backpressure, you reduce combustion temperature (thus reducing efficiency)? Reduced operating temperatures require richer mixtures (as in choking).
Every motorcycle hot rodder knows that just reducing backpressure is a hit-or-miss proposition, you need an engineered muffler or expansion chamber for best performance. Why are chain saws different? Drill some holes in the muffler and richen it up. Isn't that the same hot rod advice I got in the 50's?
Nowadays, people insulate their exhaust manifolds and turbos to keep the heat (energy) from escaping. Wouldn't that principle apply to chainsaws?
I'm not questioning the performance gains you're achieving, just questioning the mythology surrounding them.
Can anyone explain?

 

[timberwolf]

On the idle situation, it's like a water pump, open the valve up and more flows through at a lower pressure. In the case of the chainsaw motor the fuel air ratio must be kept in the same range, when the muffler is opened up flow increases, both of the air and fuel because a greater portion of the charge can escape out the exhaust port before being compressed and burnt. So even if the jet was not touched the consumption would go up as more air flows through the carb picking up fuel as it goes past. It is just that less of the fuel gets burnt without muffler restriction to keep the charge jammed back into the cylinder. Unburnt Hydrocarbons are one of the EPA targeted villains.

So you can see why EPA puts the restrictions on the muffler openings, it's 2 fold, firstly the emission of hydrocarbons and secondly if fuel consumption is reduced the other pollutants produced by the combustion process will in turn be reduced. Also increased muffler temps likely burn off other polutants for example burning CO and 02 into CO2.

I will check the cut times and WOT consumption tonight.

 

[timberwolf]

As for the need to adjust the LS, as air flow changes as does fuel delivery of the carb, no carb out there can deliver liniar fuel delivery through the range of air flow.

Also if you look at the LS orfices in a carb they are very close to the throttle plate. As this plate is held open a fraction by the idle stop even a small change to the throttle plate position will change the flow past the LS orfices. when I turned down the idle it would have changed flow past the the orfices, more air passed through a smaller space.

 

[Crofter]

Those questions take some thinking. I wanted to ask TW to make sure he did not some how get an error, which would be easy to do with that small a quantity.I did not think it would affect Idle consumption that much.
Here is a stab at what I think might be the explanation. When you open the exhaust greatly, at idle, instead of getting some of the exiting fuel charge that follows the exhaust, bounced back in by muffler pressure, it simply escapes. At idle the intake duration is longer than what is necessary to get complete crankcase filling and there is a tendency for the charge to bounce back out before the intake port closes and pull a negetave pressure that causes flow reversal in the transfers. This causes a bit of pure air to come back in the exhaust port. That is some conjecture on my part but I do know that if you take a muffler off entirely it will make your saw idle like it has a crank seal leak. In a crank case scavenged 2 stroke, the momentum and pressure occillations have a whole different scenario than a four stroke. At full throttle the momentum of the gas flow and the reduced time of opening creates a different flow pattern than at idle with only partial charge intake.
I admit that I am more of a four stroke thinker too so I wouldnt be insulted if someone comes up with a whole different explanation here.

 

[timberwolf]

Just got in from doing some cut times with the muffler modded 359, just like to say I am feeling some inner piece and enlightenment, think it's that zen thing.

Best cut time in the same 13" poplar with my chain was 4.41, thats down from 6.07 with the E tech muffler, and 9.31 out of the box with stock chain.

38% on the muffler mod
111% with muffler and chain together

Would not have believed it if I did see it with my own eyes and feel it with my own hands! lots more torque and holds 750-1000 more RPM in the wood.

Now for the bad news, redid the fuel consumption numbers.

This time I did 10 min of idle and did not touch the LS jet between tests, only the idle stop. Note the saw from new was set with HS jet maxed to the stop and LS only a hair shy of hitting the stop. That problem has since been resolved with a pair of toe nail clippers, easier than clipping your toenails.

10 min idle with the muffler closed back up (same stock opening but some of the insides changed)

40 ml of fuel @ 3200 RPM

=4.0 ml/min
1.25 ml per 1000 rotations (very close to original reading)

10 min with opened muffler (idle set back to 3200, same 500 RPM jump by reopening the muffler)

51 ml of fuel @ 3200 RPM

= 5.1 ml/min
1.6 ml per 1000 rotations ( lower than in the first test, adjusting the LS jet must have skewed the first test)

Still nearly 30% increase in idle fuel consumption.

Fuel consumption WOT no load @ 13,900 RPM increased to 58 ml/min or 4.2 ml per 1000 rotations. Thats an increase of 23%

Fuel consumption in the cut @ 11,000 RPM went up to 55 ml/min or 5.0 ml per 1000 RPM, Thats an increase of 49% consumption per min and 39% consumption per 1000 revolutions.

Square inches of wood = 9 x 6.5^2 x pi = 1247 square inches

Best cut square inches per sec = 31.42 sqr in/sec (Increase 38%)
Average Fuel consumption ml per 100 sqr inches = 3.85 ml/100sqr in (increase 6.6%)

Conclusions

Modded muffler in this case gave:
38% improved cut times
7% higher RPM / chain speed
30 % increased fuel consumption at idle
23 % increased fuel consumption at WOT no load
49 % increased fuel consumption in the cut (but at a higher RPM)

And an overall decrease in efficiency of about 7% when considering fuel burnt to wood cut.

 

[Lakeside53]

must be a slow work day up in Ontario