Where do you and should you run your RPMs on a 2 cycle engine.

[Texasmark]

I keep harping on this and it gets little attention. Personally I don't care that it doesn't. I know where to run mine and if you choose otherwise it's your equipment, your boat, your outing.

I live in N. Texas and several weeks ago we had a bad ice storm. Ice on the trees was something like a 1/4" branch was 3/4" in diameter due to the ice. Multiply that by the number of small branches and the big guys couldn't take it. Lots and lots of broken main branches.

I am still working over that pile of wood and will be for at least a couple of months but while cutting it all up for next year's fuel for my wood stove one thing came to mind:

My main cutting instrument is a nearly new 16" Stihl MS170 2 cycle chain saw. I have several unused new chains and adequate files and all to keep the chains I'm using, sharp. An added plug, I use full synthetic oil in it and it does-not-smoke, just like my OB engine on my boat.

Moving on. If I set the chain on a log with the engine idling, and then pull the trigger, the engine will lug and if I don't lift it off the log will die. Typical 2 cycle (2 stroke for you new comers) overload. Just like when you have too much prop or too much load in the stern, or too small an engine, or whatever that overloads your 2 cycle engine it just craps out........it can't take the stress.

However. If I hit the trigger a few times off the log.....rmmmm....rmmmmm.....rmmmmm, and then hold the trigger full on, running the engine up to max rpms, and then put the blade on the same log, it breezes through it, hardly loosing any rpms, wood chips going everywhere a few seconds later the cut portion falls off.

Same applies to your OB engine. Prop it to run at the upper end and it will do the same for you. Prop it for the lower end and you get what you deserve, puke for performance.

Mark

 

[dingbat]

Re: Where do you and should you run your RPMs on a 2 cycle engine.

My main cutting instrument is a nearly new 16" Stihl MS170 2 cycle chain saw.

Moving on. If I set the chain on a log with the engine idling, and then pull the trigger, the engine will lug and if I don't lift it off the log will die. Typical 2 cycle (2 stroke for you new comers) overload.

The MS170 (30.1 cc, 1.3 kW) is a 14" saw. Running a 16" bar on that power head is like to powering a 21' boat with a 75 hp. outboard and expecting a good hole shoot.

My 16", Stihl 026 (48.7 cc, 2.6 kW) kicks butt.... 150Hp on the same boat:lol:

 

[Tim Frank]

Re: Where do you and should you run your RPMs on a 2 cycle engine.

However. If I hit the trigger a few times off the log.....rmmmm....rmmmmm.....rmmmmm, and then hold the trigger full on, running the engine up to max rpms, and then put the blade on the same log, it breezes through it, hardly loosing any rpms, wood chips going everywhere a few seconds later the cut portion falls off.

Mark

In other words, RTFM.....

 

[Scott Danforth]

Re: Where do you and should you run your RPMs on a 2 cycle engine.

Texas, you need a bigger saw.

I run my old Pro Mac 650 at near an idle until I really need to go thru wood. then I give it a bit more throttle.

 

[tomhath]

Re: Where do you and should you run your RPMs on a 2 cycle engine.

Prop it to run at the upper end and it will do the same for you. Prop it for the lower end and you get what you deserve, puke for performance.

Horsepower is torque times RPM, low RPM means very low horsepower. Think about the HP difference between 500 RPM and 5000 RPM.

Of course you could go with more displacement to have higher torque. WOT on my old farm tractor is about 25 HP at 1600 RPM from a 152 ci motor. But even at idle, when you let the clutch out it goes - most of the horsepower is available.

 

[WIMUSKY]

Re: Where do you and should you run your RPMs on a 2 cycle engine.

You should be on the throttle before making contact with the log. You shouldn't lay the saw on the log and then give it throttle. Unless I'm cutting something small, I run my saw at WOT. They're built to run that way......

 

[bigdee]

Re: Where do you and should you run your RPMs on a 2 cycle engine.

You should be on the throttle before making contact with the log. You shouldn't lay the saw on the log and then give it throttle. Unless I'm cutting something small, I run my saw at WOT. They're built to run that way......

Exactly because they are direct drive. Your manual tranny 300hp pickup would stall if you tried to pull off in high gear!

 

[Tim Frank]

Re: Where do you and should you run your RPMs on a 2 cycle engine.

Exactly because they are direct drive. Your manual tranny 300hp pickup would stall if you tried to pull off in high gear!

i.e RTFM....

 

[Vintin]

Re: Where do you and should you run your RPMs on a 2 cycle engine.

When putting a chainsaw to big wood give it just a little throttle and ease it lightly onto the log as the saw is given full throttle and control engine rpm by how much you work or don't work the leverage applying dogs. Most of my Stihls are set to 13,000 no load and I aim for 9 or 10k in the cut. Hardly any of my advice can be applied to a gas powered pencil sharpener such at the Stihl 170 though.

 

[dingbat]

Re: Where do you and should you run your RPMs on a 2 cycle engine.

Horsepower is torque times RPM, low RPM means very low horsepower.

You most certainly can have high horse powers at low rpm

Torque is a measure of force. Horse power is a measure of force over time. A lot of torque in a short period could equal a smaller torque over a longer period.

T (10) x rpm (100) = 1000 hp
T(100) x rpm (10) = 1000 hp

Btw: chain saws are not direct drive

 

[Scott Danforth]

Re: Where do you and should you run your RPMs on a 2 cycle engine.

your formula should be T(lb-ft)xRPM/5252 = HP 5252 is the conversion factor for lb-ft of torque to HP. however your correct, more torque, more hp sooner in the revs.

 

[bigdee]

Re: Where do you and should you run your RPMs on a 2 cycle engine.

You most certainly can have high horse powers at low rpm

Torque is a measure of force. Horse power is a measure of force over time. A lot of torque in a short period could equal a smaller torque over a longer period.

T (10) x rpm (100) = 1000 hp
T(100) x rpm (10) = 1000 hp

Btw: chain saws are not direct drive

Yes,they use a centrifugal clutch but have a constant ratio. Above idle speed they ARE direct drive.

 

[dingbat]

Re: Where do you and should you run your RPMs on a 2 cycle engine.

Yes,they use a centrifugal clutch but have a constant ratio. Above idle speed they ARE direct drive.

a direct drive by definition contains no "slip"" component. A clutch is a slip component.

One could also make a very good argument that a clutch is a gear reduction. Thus, not a direct drive in the truest sense of the form either.

 

[tomhath]

Re: Where do you and should you run your RPMs on a 2 cycle engine.

You most certainly can have high horse powers at low rpm

Yup, that was the point I was making with the farm tractor. But I doubt anyone wants a 152 cubic inch motor on the back of their boat that only makes 25 HP. Wouldn't make a very good chainsaw motor either...

 

[bigdee]

Re: Where do you and should you run your RPMs on a 2 cycle engine.

a direct drive by definition contains no "slip"" component. A clutch is a slip component.

One could also make a very good argument that a clutch is a gear reduction. Thus, not a direct drive in the truest sense of the form either.

Your correct but I think most people understand the analogy I was trying to make.

 

[Tim Frank]

Re: Where do you and should you run your RPMs on a 2 cycle engine.

Your correct but I think most people understand the analogy I was trying to make.

Maybe, but revving up a chain saw when it is already engaged with the wood will (at least in theory)increase the wear on that clutch as opposed to letting it get up to revs before engaging.
Enough wear and there is no drive....

 

[Bubbles Up]

Re: Where do you and should you run your RPMs on a 2 cycle engine.

Your MS170 is a good small limbing saw, pulling a 16 bar is not ideal, you will lose chain speed. Personally I would make sure that chain is razor sharp. I run my saw at W.O.T. running synthetic oil. I hit the wood at full throttle. One thing that you may want to look at is doing a Muffler Mod to your saw(Google search) and re-tune carb. If you are handy do a full port on it. My MS260pro has a full port job has enough jam to pull a 18 bar , but keep it at 16 running RSC chain, diamond honed!

You may also want to look at micro chisel picco chain.

 

[nwcove]

Re: Where do you and should you run your RPMs on a 2 cycle engine.

a sharp chain, and wot is the way to go, and wot before making contact with the wood. a dull chain and low rpms are good way to end up with a nasty injury or worse. jmo

 

[Bondo]

Re: Where do you and should you run your RPMs on a 2 cycle engine.

a sharp chain, and wot is the way to go, and wot before making contact with the wood. a dull chain and low rpms are good way to end up with a nasty injury or worse. jmo

Ayuh,.... I Completely Agree,.... 2-strokers get Wot to get the job done,...

I've got a couple of Stihls, a new 290, 'n an ole 044,... both spinnin' 20" bars,...

The ole 044 is a Bear,... a sharp chain, 'n logs become blocks pretty quickly,....
The 290 is abit over loaded with the big bar, gotta baby it,... shouldn't a bought it,...

Just came in from splittin' old rounds into firewood,...
Back yards gettin' full again, with the recent ice storm, my Bud the tree guy is right out Straight,....
Couple loads of nice hard maple yesterday,....

 

[Splat]

Re: Where do you and should you run your RPMs on a 2 cycle engine.

It's been touched on, but not having the chain at full throttle before contacting the wood, and not holding it there raises the chances of kickback and other nasties substantially. Be mindful of bar position relative to your legs, and contact position of the log your cutting, mash the throttle and go.