Alaskan Mill Duty Cycle?

[lxskllr]

Although it's taken longer than expected, I'm getting close to putting a saw in wood. Just need to mount the oiler to the bar, get a couple timbers or something to put the log on, and rig up the guide system. I'd like to not burn up my new saw if possible, and when I get to the oak this fall, I'm gonna have ~20' cuts, and that'll be a lot of runtime. I was thinking it might be best to give the saw a rest during the cut. Maybe 1 minute WOT, with a 30 second rest idling? Is that reasonable? Necessary?

[YellowHammer]

I don't think you need throttle all the way back to idle, just bring the saw down to mid cruise position every now and then, and keep sawing.

I freehand ripped a monster oak the other day, and the only time I let the saw idle was when I filled it up with gas, still idling in the log, about halfway through.

More importantly is to use double oil, and richen up the carb just a little to get it off the lean side and make sure all the air passages stay clean of sawdust.  Its also vitally important to keep a sharp chain, of you will overheat and burn the bar.  

[mad murdock]

A very important thing with a csm is do not let it run out of gas.  As you may or may not know, what a saw runs out of gas it goes lean just before it quits, allowing it to go through that scenario is not a good idea especially after being pushed hard as is the cas while milling.  I always make a cut and then check the tank and/or top it off until I get a good feel for how long I can go before I need to fill it up, and don't let it run dry. I have milled a lot of wood successfully with a chainsaw, and have never burned a motor. Still running my 372 which has milled over 10k bd ft not to mention the years of firewood duty, and logging I have done with it. I use amsoil Sabre oil. Premium oil is cheap compared to a new saw. 

[Hilltop366]

I don't use a CSM myself but have wondered since it is heat that kills a saw with long runs at wide open throttle it would be nice to have a cylinder head temperature gauge, it would take all the guess work out of it.

It would be interesting to know the actual difference between different fuel/oil ratios and carb settings as well as how long it takes to cool down at idle speed after a cut etc...

[Pepe_Silvia]

I don't think you need throttle all the way back to idle, just bring the saw down to mid cruise position every now and then, and keep sawing.

I had a guy tell me it's better to keep it at WOT because you want to keep the exhaust flowing.  Any truth to that?

[mad murdock]

2 greatest factors IMO to long life of a chainsaw engine that is used for CSM are 1-keeping it clean (don't let fine sawdust build up), and 2- premium premix oil. I use Sabre (Amsoil) at about 90:1 ratio with excellent results. Besides the CSM I have run my 395XP on my Turbosawmill and have milled over 100mbf with it in the last 2 years. It is running strong!

[lxskllr]

Thanks for mentioning keeping the fuel loaded. I knew about it leaning out on some level, but I'm not sure I'd have considered it's importance during heavy milling  :^)

[olcowhand]

2 greatest factors IMO to long life of a chainsaw engine that is used for CSM are 1-keeping it clean (don't let fine sawdust build up), and 2- premium premix oil. I use Sabre (Amsoil) at about 90:1 ratio with excellent results. Besides the CSM I have run my 395XP on my Turbosawmill and have milled over 100mbf with it in the last 2 years. It is running strong!

Mad Murdock,
It appears to me that you've "logged" (wincing allowed...) a lot of hours on a CSM. I just began my CSM journey, and I'm learning a lot from these threads. I'm running a new Stihl MS 661CM. Where do I find premix?

[YellowHammer]

I don't think you need throttle all the way back to idle, just bring the saw down to mid cruise position every now and then, and keep sawing.

I had a guy tell me it's better to keep it at WOT because you want to keep the exhaust flowing.  Any truth to that?

No, I spent decades testing and evaluating service life of engines, and WOT is more detrimental than cruise power.  The rule of thumb is that 90% of engine wear is in the last 10% of throttle, especially 2 strokes.  So even though they are capable of WOT and max RPM, it causes more wear, and since typically WOT is based on both max rated RPM and max rated cyclinder head temperature, any issues with the mixture are very detrimental.  

Basically the engineering margin is thinnest as WOT or max rated power.  That's way it's vitally important to keep the cooling air passages clean.  Operating temperature are the life of the chainsaw.  The engine must stay cool, and in an air cooled engine, keep the air passages clean.  Don't over rev the saw, and don't lug it.

That's exactly why the warnings about running out of fuel while high throttle are true, the carbs run out of fuel, the mixture leans up, and a lean mixture runs hotter and increases RPM over rated and exceeds the safety margin.  The engine burns up.  

The way to run an engine cooler is to actually richen the mixture, which moves the equivanlence ratio even further from ideal and causes the engine to run cooler because it's at the same throttle setting.

The proper oil is also critical, as most oil bases start to break down at the temperatures where the engine needs it most, at the hot end.  Amsoil, Lucas, Stihl are some we have exhaustively tested and all are very good.  

[Brucer]

Just to reinforce what the experts are saying, when I was running a CSM I set the carburetor to run a little rich and had no issues with running the engine flat out.

I also made a point of killing the engine at the end of the cut by pulling the choke, rather than using the switch.

[Tropical Sawyer]

I used to do alot of chainsaw milling with an ms660. Probably the most important thing is the keep the revs high and not bog down the saw to much while in the cut. Definitely run the saw at WOT during the cut while the saw is engaged with the wood as it keeps air flowing throughout the saw.

The only time the 660 got really hot was on a 30" "sea poison" log but if you are paying attention to the saw you will realize when the temps are getting a bit high and and can avoid doing any damage. 

When I was doing consecutive long cuts I would usually run the saw out of the cut with no load (at half throttle) for approximately half a minute after each pass to to let the internal fan do its work and cool the saw. I wouldn't suggest doing this at WOT though as that would probably be detrimental to the saw.

Only other advice would be to keep alot of wedges in the kerf close behind the saw. This really lowers the friction on the bar and makes it much easier to push through the log. Try to keep wedges on both sides of the log and use them to open the kerf an even amount on each side to keep the cuts straight.

[Hilltop366]

That's exactly why the warnings about running out of fuel while high throttle are true, the carbs run out of fuel, the mixture leans up, and a lean mixture runs hotter and increases RPM over rated and exceeds the safety margin.  The engine burns up.  

And because the oil is supplied by the gas/oil mixture it is getting less oil as well as less cooling effect by the fuel.

[mad murdock]

Any amsoil dealer can get you Sabre oil.  Or high grade oil from a good saw shop.