Any way to tell if a air leak vs lack of oil caused a saw to burn up?

   / Any way to tell if a air leak vs lack of oil caused a saw to burn up? #31  
It kinda interesting the Stihl has the 4-mix 4 stroke engine in trimmers, weed whackers, and such. Can't find one in a chainsaw. Anyone know if they offer their 4-stroke in a chainsaw?
 
   / Any way to tell if a air leak vs lack of oil caused a saw to burn up? #32  
MossRoad said:
If you compare dirtbikes, 2 strokes VS 4 strokes, they pretty much had to double the engine displacement class to get the same speeds.
Click to expand...

Two stroke has a power stroke every turn, four stroke has a power stroke every other turn. A 250cc 2-stroke and 500cc 4 stroke actually have equal volumetric displacement.
 
   / Any way to tell if a air leak vs lack of oil caused a saw to burn up? #33  
Sodo said:
Two stroke has a power stroke every turn, four stroke has a power stroke every other turn. A 250cc 2-stroke and 500cc 4 stroke actually have equal volumetric displacement.
Click to expand...

There is a whole lot more to it than that. The displacementnis still the same. 2 strokes have twice the power strokes for a given rpm, but that don't quite equate to twice the power though.

2-strokes don't have valves. And don't have a cycle for exhausting gas or intaking gas. Rather everything kinda overlaps. Exhausting at the same time as intaking, then starring compression while exhaust is still open. And opening the exhaust early in the power cycle. That's why on dirt bikes there is alot of science in the exhaust and why they have " power bands". On a saw however without a pipe, it wouldn't take double the displacement to equal the same power. 25% more of around there. The issue is weight. Lots more moving parts and adddd weight
 
   / Any way to tell if a air leak vs lack of oil caused a saw to burn up? #34  
4 strokes are more efficient, too. I used to drag race a two stroke twin Yamaha RD400. It would eat pretty much every 4 stroke up to 750cc with ease. That's where it shined: going really fast. You had to keep it at high revs in the power band area to get good power out of it. But man it would suck fuel down! I wonder what the optimum speed for a chain saw blade is and how much power is required to keep it at that speed when it starts biting wood? I also wonder what the torque curve is on a 2 stroke chainsaw and a 4 stroke (if there is one). Would make for some good reading. :thumbsup:
 
   / Any way to tell if a air leak vs lack of oil caused a saw to burn up? #35  
BTW, chainsaws don't have blades, they have bars.

And I know from personal experience with 2 stroke engines, that the ethanal issues are real. I've been to shops that try to repair the carbs, and end up replacing them due to the labor cost of putzing with rusted internal jets, orifices etc. that can't be brought back to specs, or close enough to run right. There are so few adjustments that work effectively on the crappy carbs they make these days, that have to comply with the emissions regs that keeping things running right is next to impossible, unless one is very strict on what they run in what machine.

And a 79 Jeep engine is not a 2 stroke. Running carb cleaner through it's carb might have cleaned it up, but that has no reference to how 2 strokes have been plagued by emissions and ethanol/crappy carbs, etc.
50 engines, must be proved by a picture of them with #s attached! It's required.:thumbsup:
 
   / Any way to tell if a air leak vs lack of oil caused a saw to burn up? #36  
Well at least we agree part of the problem is that people have to take their problems to the shops. Where (IMHO) they will tell you that your large repair bill is the fuel's fault, not their inability to fix it efficiently while the next guy is willing to give them $85/hr. Perhaps exaggerate a little to soften the blow.

That is the new world.

I'm a tinkerer, this stuff your dad used to do is easy for me, so I'm not afraid of it, willing to take the chance. But in the last five years, since I gave up on the ethanol legend I've had to do nothing, to 50+ engines. Hence my conclusion. I feel like 5 years is enough time. I've had ethanol in my engines at least 15 years. I do not prefer it.

I'm certain that folks are having general problems but I'm not. I was surprised for a few years but the surprise has diminished.
 
Last edited:
   / Any way to tell if a air leak vs lack of oil caused a saw to burn up? #37  
The only problem that I've had that I will attribute to ethanol is my fuel lines in several chains saws turned to mush... and at that, I can't prove it was the ethanol. Other than that, I've been running everything, cars, trucks, motorcycles, tractors, lawn equipment, generators, etc... on 10% corn for probably 20 years with no problems that can be attributed to ethanol.
 
   / Any way to tell if a air leak vs lack of oil caused a saw to burn up? #38  
Couple of points to ponder:

A 4-stroke is less of a power/weight detriment to a saw than it is to a motor-cross bike. In the bike the mass of the engine detracts from the velocity accel-decal, and cornering of the bike. A chainsaw engine doesn't move it's own weight like a bike. Only slight arm powered movements from saw cut to cut.

As stated before: A 2-stroke is less powerful than 2x the cc 4 stroke counterpart because of intake and exhaust design compromises.

A "4-mix" is not a good representative of a 4 stroke. Too many design compromises.

Biggest obstacle for 4-stroke in chainsaw isn't weight. It's being able to provide fuel and lubrication in all positions ie..upside down.
( Honda has a small 'true' all position 4-stroke, but there are reports of varying longevity based on engine orientation)

Carburetor/air cleaner is big sizing problem in single cylinder 4-strokes. Must be made very oversized for engine output as these pieces spend 75% of their time inactive, and must be oversized for a single brief event.
 
   / Any way to tell if a air leak vs lack of oil caused a saw to burn up? #40  
You must log in or register to reply here.
 

Footer Links 1

Top