066 Poly vs Metal

[Crofter]

Lakeside, is it your feeling that it was the engines power pulses that was breaking the crank or the impact of engaging the chain brake at high Rpms. In either case a higher inertia/momentum flywheel puts more strain on the crank. Where was the most common break; flywheel side or clutch side?

 

[Lakeside53]

The break was almost always on the flywheel side...

Stihl's theory was that it was primarily due to the engine.. The flywheel/crank was pretty much the same as the 064, and the 064 didn't have that problem. Some operators didn't help either though...

 

[bwalker]

Flywheel weight doesnt effect output.........

 

[klickitatsacket]

Flywheel weight doesnt effect output.........

what do you mean by this? It may not effect HP but it certainly effects the torque band and RPM.

 

[Lakeside53]

Why would it affect rpm?

 

[bwalker]

It may not effect HP but it certainly effects the torque band and RPM.

A lywheel weight will not change the out put, torque, horsepower, power curve etc....
It will change the operational charachteristics in that it will slow down response to changes in load. The rpm will remain the same it may just take a but longer to get there.

 

[bwalker]

BTW if horsepower isnt effect, either is torque as HP is calculated using the formula horsepower = torque * rpm / 5252.

 

[klickitatsacket]

because the rotational mass weighted to the outsidetakes more torque to spin, thus robbing RPM.

I explain HP to most people like this. A little mental picture

HP is a function of RPM and Torque. Think of HP as a center fulcrum on a see-saw. Torque on one end and RPM on the other. IF the HP does not change and as one goes up the other goes down, with both being set on a bell curve and neither being able to zero out (let's not get into a steam engine discussion either on this point) The only way to raise both is to increase HP. So if more Torque is required to turn a greater rotating mass then the RPM will be reduced.

Now earlier you asked about timing. There is not a woodruff key I do not remove when building a saw. Remember if all things are equal. Let's stick to the basic idea with out trying to throw other factors in the mix.

 

[klickitatsacket]

Back in the morning. I have to take my son to a wrestling match. BTW this is a great discussion.

 

[Lakeside53]

Sorry.. I don't buy the RPM argument.. It MIGHT take a little longer to get here (real little) but only the bearing friction or air friction (from pumping air) will hold it back.. and I doubt that's significant.

 

[klickitatsacket]

Andy, you do not have to buy it. You have access to saws go try it.
(I am waiting for my wife to show up so that we can go)

 

[Lakeside53]

Andy, you do not have to buy it. You have access to saws go try it.
(I am waiting for my wife to show up so that we can go)

There must be other factors involved other than a relatively minor change in flywheel weight. You can't jusify changes in the laws of physics based solely upon observation.

 

[bwalker]

Dean, physics aint on your side.
I dont know why two differant 066's act differently, but can only guess that somehting is differant between the two other than the flywheels. Timing, rod length, porting, ignition box, porting, tolerances and the last goes on.
My point is you can compare two differant saws and say one behaves the way it does based on one factor when many otherfactors can be differant as well.

 

[klickitatsacket]

you guys crack me up. Ben you just put the math on the thread (basic elementry math at that) Plug in the numbers.

Does it take more or less torque to move a heavier rotaional mass and maintain spead? Any one? Any one? Any one? Yes, you kid in the back sleeping. Uhhh???? More? Yes. You can go back to sleep now.

So if it takes more torque to attain this and knowing that HP has not changed then what must decrease? Hint, it's the other one. You got it; RPM

 

[hautions11]

Let me jump in to this discussion. Two saws, theoretically identical HP and Torque. In the cut both running 10k RPM. One saw has more rotational mass then the other. With the variations in load during a cut coming from operator input, pushing on the dogs, density changes in the wood, thicker and thinner cross sections as you move through a log etc etc etc. If these changes and variations are subtle, the saw with higher rotational mass will maintain a more constant RPM. We all know from running saws, due to their fine line of power band, when the loads on the saw become too great, the RPM falls off just a little bit more, the saw falls on it's face and bogs. The saw with a higher rotational mass will be more likely to power through a momentary high load and stay in the power band then the saw with less momentum. They will all be overcome at some point, the momentum simply stave's off the momentary high loads that often occur during a cut.

 

[bwalker]

Dean, I dont have the time nor energy to argue with you. Your incorrect, althought intuitivly what your saying seems reasonable.

 

[spacemule]

Does it take more or less torque to move a heavier rotaional mass and maintain spead? Any one? Any one? Any one? Yes, you kid in the back sleeping. Uhhh???? More? Yes. You can go back to sleep now.

Inertia says that objects in motion tend to stay in motion. The only forces within the saw that counteract inertia is friction from the bearings both supporting the crank and within the connecting rod ends. Therefore, it follows that the only additional force counteracting inertia between a heavier flywheel and a lighter one must be any additional friction on the bearings imposed by the increased weight. Since the bearings in a saw are inherently efficient, they eliminate nearly all rotational friction. We must, therefore, conclude that the additional force necessary to maintain momentum of a heavier flywheel must be negligible.

 

[Lakeside53]

I thought I said that, but Space, you did the longer verison and did it well!!!

Sorry Dean, you are wrong on this one...

 

[klickitatsacket]

lake I am sorry that I wasted my time with people who only want to argue. Plug in the #'s in the equation. Walker quit argueing because he finally realized the math does not lie. You; I have no clue why you would even argue the point unless it was that difficult a concept to comprehend.

Space you are right; I slipped the "maintain" in there when I was actually thinking on the lines of acceleration. My bad and thank you for pointing it out.

 

[Lakeside53]

I have no idea what you are now talking about. I'm saying what Space is saying, and you're now saying Space is correct... Maintaining the momentum is what we are talking about - RPM...