Big CC Chainsaws a thing of the past or will new models come out soon?

[Robin Wood]

Makes a fair old difference though. You think about the weight in a flywheel with the magneto inserts plus the weight of a large pro-saw clutch. The magneto inserts and the clutch pads all being on the outside of the "wheel" mean more mass effect too. All the old steam engines had massive flywheels so they could put more weight on the outside of the wheel as they could have less weight on the wheel but more torque! You could have a light weight crank and add a little weight to the outside of flywheel to give a lighter saw but keep the flywheel torque factor. 

Precisely, i call it the pendulum effect. The weight will self sustain a good bit when power drops from moving the load, feels like the weight will assist in a lever like effect.

My brother in law works in oil barge, their 40ft long engines have special weights on the crank web. He said we wasnt aware of that concept until we spoke about it, the other day he rang me and said everything make sense now and he said when they shut the engine off. It'll free spin couple rounds shaking the whole ship before coming to a full halt, he says he can feel the weight swinging and going back and forth abit before stopping completely. I hope im not boring you folks with too many details lol

[trigger_andy]

4 hours ago, Rough Hewn said:

I find the teeth can wear down to blunt from a new .404 chain in 2’ of very very seasoned ash. Guy I chat with in Australia uses a 25” bar on his highly modded 880.

I'm planning on resawing some well seasoned 5" Ash slabs in half. Guess I'll have to up my sharpening game if I wanna get through the full length of them.  

[Khriss]

1 hour ago, Robin Wood said:

Precisely, i call it the pendulum effect. The weight will self sustain a good bit when power drops from moving the load, feels like the weight will assist in a lever like effect.

My brother in law works in oil barge, their 40ft long engines have special weights on the crank web. He said we wasnt aware of that concept until we spoke about it, the other day he rang me and said everything make sense now and he said when they shut the engine off. It'll free spin couple rounds shaking the whole ship before coming to a full halt, he says he can feel the weight swinging and going back and forth abit before stopping completely. I hope im not boring you folks with too many details lol

Nice to have more technical weight on the forum  !! 

 

Anyway Mr@Stubby those Christmas slippers..? Tartan again or those hilareous hedgehog onez? K

[Stubby]

3 hours ago, Robin Wood said:

Precisely, i call it the pendulum effect. The weight will self sustain a good bit when power drops from moving the load, feels like the weight will assist in a lever like effect.

My brother in law works in oil barge, their 40ft long engines have special weights on the crank web. He said we wasnt aware of that concept until we spoke about it, the other day he rang me and said everything make sense now and he said when they shut the engine off. It'll free spin couple rounds shaking the whole ship before coming to a full halt, he says he can feel the weight swinging and going back and forth abit before stopping completely. I hope im not boring you folks with too many details lol

The stored energy in a big flywheel is let out in the form of inertia .  Takes a bit of time to spin up but keeps spinning even when the power is off  .  Look at your brush cutter . Spins up quick and stops quick with line . Spins up slower until full chat and takes much longer to stop with a metal blade on .

[shavey]

6 hours ago, Robin Wood said:

088 crank 742g
3120xp crank 839g
070/090 crank 945g
1200 crank 1,028g

I'll need 166 dolmar crank weight someday to complete these data's for my research

I believe the farm tractor folks will understand what im up to here

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Robin you should ask Lee about the 166 crank I cant remember bore and stroke 

On the CT and 166 was 56mm x 48mm

And another was mcculloch SP 125 was another long stroker

 

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Edited November 26, 2020 by shavey

[Moose McAlpine]

5 hours ago, Robin Wood said:

My brother in law works in oil barge, their 40ft long engines have special weights on the crank web. He said we wasnt aware of that concept until we spoke about it, the other day he rang me and said everything make sense now and he said when they shut the engine off. It'll free spin couple rounds shaking the whole ship before coming to a full halt, he says he can feel the weight swinging and going back and forth abit before stopping completely. I hope im not boring you folks with too many details lol

 

The shaking is the engine's momentum fighting compression, not the weights*. Diesels have to be choked to shut down smoothly. You see diesel engines with a "throttle" which is actually an anti-shudder valve. It closes when the engine is switched off, creating intake vacuum to reduce the engine fighting compression and allowing a smoother shut down.

 

You see it in cars and vans, not seen it on large engines.

 

*Large diesel engines use bolt-on crank balance weights, reduces the size of forging required to make the cranks and allows easier balancing. It's found in truck engines up to marine and stationary engines.

[Mrblue5000]

Does anyone watch Iron horse on youtube? I think he's aiming for lighter pistons, not sure about the crank though. A lighter piston would probably improve acceleration but would it change the torque figures? 

[bmp01]

2 hours ago, Stubby said:

The stored energy in a big flywheel is let out in the form of inertia .  Takes a bit of time to spin up but keeps spinning even when the power is off  .  Look at your brush cutter . Spins up quick and stops quick with line . Spins up slower until full chat and takes much longer to stop with a metal blade on .

Nearly Stubby, been here before havent we....

 

Inertia is what something heavy has - its the resistance of the heavy thing to change speed. You have to put energy into or take out energy from the heavy thing to change its speed. A flywheel is a special case because it's a rotating thing,  the flywheel effect that we understand is called "moment of inertia". The same rules apply though, to make it spin faster you put energy into the flywheel, and take energy out to make it go slower.

Through a single engine cycle, energy is put into the flywheel (combustion) and taken out (over coming compression, powering the power take off etc). Importantly, a flywheel can not produce power on its own. It can give up some of its energy over several engine cycles but the result is that the engine slows down. "Big" flywheel with high moment of inertia has lots of energy so slows down less if you take out same energy per cycle.

Moment of inertia is calculated as mass multiplied by radius squared, easy to work out for the pendulum, not so easy for flywheel, crank, rod and piston. But there are bits of kit to meaure moment of inertia and a CAD systm will have at calculating it. As mentioned above you can have a big diameter, light flywheel having same moment of inertia as a small diameter, heavy flywheel.

 

 

[Robin Wood]

 

Uncle Lee is the guy to talk when it comes to dolmar 166, i think it could have lower bore size like 52mm maybe. But stroke is 48mm i remember that, uncle lee has a hybrid 166 with 090 top end. They got a video of it running 72" bar in upstate gtg couple years back.

Uncle and I go way back, i sent him 3 units of 1201 and took me few years to find a good used 1200 to complete his big echo collection. Half of the 166 exist on the planet could belong to him, he had like 30 over 166s! At some point

He loves muscle saws, sent him a NOS Jonsered 920 last month. Last i heard his collection was close to 500 saws

[Robin Wood]

 

The shaking is the engine's momentum fighting compression, not the weights*. Diesels have to be choked to shut down smoothly. You see diesel engines with a "throttle" which is actually an anti-shudder valve. It closes when the engine is switched off, creating intake vacuum to reduce the engine fighting compression and allowing a smoother shut down.

 

You see it in cars and vans, not seen it on large engines.

 

*Large diesel engines use bolt-on crank balance weights, reduces the size of forging required to make the cranks and allows easier balancing. It's found in truck engines up to marine and stationary engines.

I thought they released compression a little to make stopping less violent? you're right marine engine are very close in terms of design with chainsaws. 2 stroke diesel with uni flow scavenging i believe? Ours is piston ported 2 stroke loop scavenging

 

The weight is concentrated at this web i was told