Sprocket change out to increase torque with larger CC saws.

[purellbear37]

Thoughts or share outs?

Does it make sense to do this?

I have large CC saw that I have dedicated to large trees and large bucking, wondering about min and maxing the saws ability.

I do 90% firewood work.

Something I have been thinking and curious about.

 

[HumBurner]

Gear down for torque, gear up for speed.

What saw is it?

 

[NSEric]

Most all saws come with the smallest sprocket possible on them, so you likely cant gear down any further then stock.
Get good at sharpening chains and matching them to the saw and wood you're cutting, this is about the only place you will find any gains.

 

[epo]

The torque remains the same. What changes is the lever arm depending on the diameter of the drive sprocket, which depends on the number of teeth/pins in it.
More teeth/pins, larger diameter, longer arm, less force acting on drive links, higher chain speed.
Fewer teeth/pins, smaller diameter, shorter arm, more force acting on drive links, lower chain speed.

 

[barfer]

The torque remains the same. What changes is the lever arm depending on the diameter of the drive sprocket, which depends on the number of teeth/pins in it.
More teeth/pins, larger diameter, longer arm, less force acting on drive links, higher chain speed.
Fewer teeth/pins, smaller diameter, shorter arm, more force acting on drive links, lower chain speed.

You’re 100% right about the deltas in chain length (diameter) and the rest of it.

But gearing changes (ie sprocket teeth changes) have a torque impact on as well. On motorcycles they have loads of online calculators that will tell you top speed and torque deltas for gearing up or gearing down whether front sprocket or rear sprocket…. and one suffers at the increase of another…

ie if you want more torque you’re gonna end up limiting your final top speed maximum.
Gearing for higher chain speed will cost you a torque penalty…

but unless OPs chainsaw suffers torque issues he’s not going to be bothered by a one tooth torque reduction.

But even a single tooth of sprocket change makes an appreciable difference… (for example on a motorcycle increasing the front sprocket a single tooth can increase top speed gearing by ~10 mph… (depending on the bike and the rear sprocket) if you’re riding a torque monster lots of guys will do this to ride dirtbikes on the freeway or if they’re doing a desert race take their max speed from 65 mph to 75 mph)

 

[epo]

You’re 100% right about the deltas in chain length (diameter) and the rest of it.

But gearing changes (ie sprocket teeth changes) have a torque impact on as well. On motorcycles they have loads of online calculators that will tell you top speed and torque deltas for gearing up or gearing down whether front sprocket or rear sprocket…. and one suffers at the increase of another…

ie if you want more torque you’re gonna end up limiting your final top speed maximum.
Gearing for higher chain speed will cost you a torque penalty…

but unless OPs chainsaw suffers torque issues he’s not going to be bothered by a one tooth torque reduction.

But even a single tooth of sprocket change makes an appreciable difference… (for example on a motorcycle increasing the front sprocket a single tooth can increase top speed gearing by ~10 mph… (depending on the bike and the rear sprocket) if you’re riding a torque monster lots of guys will do this to ride dirtbikes on the freeway or if they’re doing a desert race take their max speed from 65 mph to 75 mph)

There is a difference between a chainsaw and a motorcycle. In a chainsaw, we are interested in what happens to the chain. And that, in the case of a modern chainsaw, depends on the torque/rpm of the engine and the number of teeth/pins in the drive sprocket. In the case of a (classic) motorcycle, the chain is used to transfer power to the drive wheel. In this case, of course, we are interested in what the gear ratio will be.

 

[barfer]

There is a difference between a chainsaw and a motorcycle. In a chainsaw, we are interested in what happens to the chain. In the case of a (classic) motorcycle, the chain is used to transfer power to the drive wheel. In this case, of course, we are interested in what the gear ratio will be.

Certainly

Chain speed is chain speed.

“The real issue here is what is the optimal sprocket for the user’s objective?”

Manufacturers are subject to regulations EPA noise whatnot so they do things like put baffles in exhaust and gear down for noise.

If the objective is to cut wood you want the fastest chain speed you can get that has enough torque to cut the wood.

All motors have their own torque curve… a 40cc is different than a 70 than a 90 etc

If you cut soft wood you don’t need as much torque than somebody cutting hardwood. The firefighter guys sometimes cutting through metal or whatever have different needs too…

So I’m all in favor of swapping sprockets to optimize.

I’m just saying there is a price. You know that whole equal and opposite reaction principle?

For the sake of ridiculous example if you could somehow fit a 100 tooth sprocket on a saw your chain would spin at outrages speeds but it would suffer a serious torque penalty and cut more like a high speed dremel type tool instead of, for instance… a chainsaw…

Peace my brother

 

[Mad Professor]

Pay attention to setting your rakers for the type wood being cut, and length of bar you are using.

Changing # of sprocket teeth is a big jump.

 

[barfer]

I should make my definitions clear. When I say torque I mean torque useable at the bar… as opposed to how much torque the motor generates at the flywheel.

Because you’re right torque and HP at the flywheel are what they are and no amount of sprockets or chain length will change that.

But at the end of the bar yes absolutely there is a measurable difference in torque power delivery subject to bar length chain length sprocket etc.

 

[sean donato]

Torque is torque, gearing is just that, gearing. Trying to over complicate something simple is stupid. Smaller sprocket lower chain speed= geared lower. Bigger sprocket faster chain speed= geared higher.

 

[epo]

I really don't know where you see the problem. With an engine with certain characteristics, you can increase the linear speed of the saw chain by using a drive sprocket with more teeth/pins. This is done, of course, at the expense of the force acting on the drive links.
T = F x r
In the case of the system drive sprocket-chain-guide bar, unlike a motorcycle, what's at the tip of the bar doesn't really matter. There may not be a sprocket there at all.

 

[barfer]

I really don't know where you see the problem. With an engine with certain characteristics, you can increase the linear speed of the saw chain by using a drive sprocket with more teeth/pins. This is done, of course, at the expense of the force acting on the drive links.
T = F x r
In the case of the system drive sprocket-chain-guide bar, unlike a motorcycle, what's at the tip of the bar doesn't really matter. There may not be a sprocket there at all.

I think we agree we’re just talking past each other. When you say “at the expense of the force acting on the drive links” I mean torque.

No big deal, brother. Chainsaws have “force acting on the drive links” to spare so unless the user is using a very low HP saw and trying to cut sycamore with a 48 inch bar the user isn’t going to care about the torque expense.

 

[Haywire Haywood]

We need an aftermarket bolt-on 2:1 gearbox.. then we'll get the chain speed of an old reed valved early 70s torque monster saw with an autotune 2024 engine. Of course now you've disconnected the oiler from the bar.. will have to build in a passthru passage on the gearbox to get it to the bar.

 

[barfer]

We need an aftermarket bolt-on 2:1 gearbox.. then we'll get the chain speed of an old reed valved early 70s torque monster saw with an autotune 2024 engine. Of course now you've disconnected the oiler from the bar.. will have to build in a passthru passage on the gearbox to get it to the bar.

I love it!!!

 

[Philbert]

What pitch, cutter type (full-chisel, semi-chisel, etc.), and sequence (standard, skip, etc.) chain are you running?

Have you optimized your sharpening angles for the type (species) and condition (green, dry, etc,) that you are cutting?

Sometimes, these small things can make a big difference.

A smaller sprocket might make a difference: the easiest thing to do is try, it and see if it is noticeable to you.

Should not be too expensive to try, assuming that you have a rim sprocket. Maybe $10 for the rim, and maybe have to take out a link of chain on a test loop (another $6 to $10 if you have to pay someone to do it?).

Try it side-by-side in the same wood with your current set up, and let us know what you find out!

Philbert

 

[epo]

We need an aftermarket bolt-on 2:1 gearbox.. then we'll get the chain speed of an old reed valved early 70s torque monster saw with an autotune 2024 engine. Of course now you've disconnected the oiler from the bar.. will have to build in a passthru passage on the gearbox to get it to the bar.

Take a look at Zenoah RC6200P. A belt is used for power transmission. You can also see the line run between the powerhead and the attachment. They use it to cut roots.

 

[chilipeppermaniac]

What saw are you using, purellbear?

 

[sean donato]

I think we agree we’re just talking past each other. When you say “at the expense of the force acting on the drive links” I mean torque.

No big deal, brother. Chainsaws have “force acting on the drive links” to spare so unless the user is using a very low HP saw and trying to cut sycamore with a 48 inch bar the user isn’t going to care about the torque expense.

force= torque in the case of an engine any time you can get something in the drive line with the gearing the felt torque is changed, better or for worse. Don't bother trying to explain it to him, he will argue till you're blue in the face and throw every equation and anything else he can find on the internet to prove you're wrong, when in fact you're absolutely right.

 

[RedneckChainsawRepair]

Take a look at Zenoah RC6200P. A belt is used for power transmission. You can also see the line run between the powerhead and the attachment. They use it to cut roots.

View attachment 1205119
View attachment 1205121

I never seen something like that today. Going to save your info and share elsewhere.

 

[Mad Professor]

Take a look at Zenoah RC6200P. A belt is used for power transmission. You can also see the line run between the powerhead and the attachment. They use it to cut roots.

View attachment 1205119
View attachment 1205121

I never seen something like that today. Going to save your info and share elsewhere.

That is an interesting attachment.

Does the Zenoah share same bar mounts with other saws? Also would like to see detail of the clutch belt drive system and if that could be adapted. Is it just a special rim for the clutch drum?

I still save my old bars/chains/rims for "stumpers" and/or trees that might have metal in them.