066 Poly vs Metal

[Crofter]

Removing all doubt!

Cut4fun, comparing the two flywheels with all subjective input removed would be interesting. The initial, as well as the running timing curves would have to be graphed to make sure that timing was not responsible for any differences observed in performance. Even two identical part # coils or flywheels may show different timing curves. Parts would have to be swapped on the same saw because two saws with consecutive serial numbers can have cylinder casting variations that can make considerable difference in port timing numbers and compression. You have to be very carefull something unthought of does not give you the wrong answer.

 

[Lakeside53]

Ever have an 066 snatch back the recoil handle from you? You need flywheel weight to help carry you past compression and I believe, before top dead centre ignition. A bit more flywheel is a plus for starting. Never had a 064 in my hands but with an 066 you gotta show it authority or it will laugh at you!

Nasty nasty saws...

A few times a year (usually on a frosty morning!!) I get an 064 that's been messed with... and the flywheel put back on the wrong slot. The ignition is way out and it literally rips your fingers off! Every time I get an 064 in with a non-elastostart, I get nervous (whoch make the likelyhood of a problem worse!!) .

 

[Lakeside53]

Poly flywheel pictures

Here's the pictures of the 066 poly flywheel. Any resemblance that that of Wagonwheelers 066 is purely coincidental:biggrinbounce2:

the rewind hub is aluminum; the rest of the metal is steel

 

[Lakeside53]

I didn't have an 066 Aluminium flywheel I wanted to cut up... Maybe next week, or if someone else has one to post...

 

[bwalker]

Do the 064 and 066 use the same crank cases?

 

[hautions11]

No. The bolt pattern for the cylinder is different for one thing.

 

[Mr.]

I stopped reading on page 4 or 5. If anyone has ever had a dirtbike they know that a heavy flywheel helps put it to the ground.

Freak stated another observation very well about his mustang.

IT STANDS TO REASON. If the stored energy is enough to break the crank it could be enough to be helpful.

Everyone here has a dog in the fight before anyone says anything about it.

WE cannot explain every characteristic of these engines. We can TRY. If we try together we learn if we try apart we make unnecessary mistakes.

Fred

 

[timberwolf]

Work saw or race saw? hot start or cold start? one cut or three?

I would venture that the ideal flywheel weight will depend on the application.

Would a drag race, a road or offroad racer use the same flywheel weight? Unlikely.

Improved spool up does not win many points for an 066 work saw, nor would poor idle and hard starting created by a light weight flywheel. But on a cold start 3 cut race, geting up to RPM faster and picking up RPM in changeovers should favor a lighter flywheel.

 

[Mr.]

Another point to be made is a single cylinder engine must conserve energy post "power stroke," enough that it seems seemless to us that the two stroke engine turned over once against force (compression stroke.)

Someone can tell me that fraction of a second, but it is much much smaller than .25 sec and earlier discussed.

IT STANDS TO REASON: If you can conserve energy from the power stroke until the end of the compression stroke more effectively.....then we have more useable power and less power robbing dynamics.

As earlier stated the flywheel STORES energy.

Fred

 

[Mr.]

Work saw or race saw? hot start or cold start? one cut or three?

I would venture that the ideal flywheel weight will depend on the application.

Would a drag race, a road or offroad racer use the same flywheel weight? Unlikely.

Improved spool up does not win many points for an 066 work saw, nor would poor idle and hard starting created by a light weight flywheel. But on a cold start 3 cut race, geting up to RPM faster and picking up RPM in changeovers should favor a lighter flywheel.

Was this post in response to me? I didn't even mention chainsaws.

Fred

 

[bwalker]

stopped reading on page 4 or 5. If anyone has ever had a dirtbike they know that a heavy flywheel helps put it to the ground.

Yep, but thats a far cry form making more torque and changing power curves..

WE cannot explain every characteristic of these engines. We can TRY. If we try together we learn if we try apart we make unnecessary mistakes.

Wouldnt you agree thats its tough to learn when poor and incorrect information is being passed around?

 

[CrazyCarl]

And here we go!!!!!WOO HOO!!!!!!!!!

Stored energy is a good thing,but once released the motor(engine) must be able to Repeat the process.Hence the need for horsepower.Torque is only good to begin the process.Horsepower is needed to continue the process.

 

[timberwolf]

Carl, Think you may want to look into HP and torque a bit more, HP is torque at a given RPM, they are all interelated.

Torque is only good to begin the process.Horsepower is needed to continue the process.

This is confusing, horspower does not exist on its own, it is a function of torque and RPM.

Fred, To take a saw at 12500 RPM, with a exhaust opening 90 deg ATDC, the inertia of the crank, flywheel, sprockets and chain to an extent needs to carry the engine roughly 270 deg until TDC, so that would work out to 0.0036 seconds.

If this saw put out 5 ft/lb of energy as a measured average, the peek torque will be over 4 times that value, likely closer to 8 times as all energy is imparted to the crank in only 90 of the 360 deg of rotation, in reality less than that as torque at TDC is zero and at 90 deg ATDC it will be dropping back down. I think it should be possible to calculate the energy the flywheel will store per revolution, assuming an even weight distribuation in the flywheel and compare this to the energy required to compress the fresh charge.

Energy can not be created or distroyed, so what ever goes into the flywheel must come back out.

So the motive energy going into the flywheel = the motive energy out of the flywheel minus losses to friction (air movement) and minus heating of the crank. Every time a rotational force is placed on the crank, it twists it, moving the metal internaly and causing heating, as long as the the flexing remains within the elastic limits of the crank material and as long as the thermal imput into the crank does not exceed it's ability to disipate the heat the crank should hold together. Thinking along that line it is easy to see where a heavy fly wheel could cause greater flexing (twisting) of the crank and would contribute to crank breakage.

 

[Kneejerk Bombas]

So the motive energy going into the flywheel = the motive energy out of the flywheel minus losses to friction (air movement) and minus heating of the crank.

What about the drag from the magnetic field past the coil?

 

[Mr.]

This is almost embarassing, but I have to ask.

Are you agreeing or disagreeing with me TWolf? I think you are building from my premise, so either way or no way it's good.

You are right about the flywheel not creating energy, but it definately can change characteristics of the engine.

Isn't the flywheel basically an extension of the crank when bolted into place? I do not believe any conservation THEORY is affected by the fact one can remove the flywheel from the crank.

Fred

 

[Mr.]

Good point Mike. I'm not sure the push and pull would not cancel each other out, but definately affecting it.

Fred

 

[timberwolf]

Good point mike, there would be the reluctance of the magnetic field as well as the energy use to generate the spark and any electical losses involved.

Fred I think we are in agreement. Except I think the role of a flywheel in a chainsaw and a bike don't compair that well. At least in terms of a cold start race saw with a powerband less than 1000 rpm up near 14,000 rpm.