When Milling or Cutting in big timber what parts recieve the most wear???

[Nik_Danger]

Yet another question from Nik_Danger...
When milling or cutting big timber that stresses a saw what parts are really receiving the stress? Is it just the piston, rod and crank? As some of you know I am pondering the idea of buying a 3120 for milling only...but thats a lotta green for something when you also have a tool that WILL do the job at hand. If its just the internals of the engine that wear prematurely on a smaller saw (660) then I would be inclined to just do rebuilds and save over the bigger saw. I looked on baileys yesterday and was amazed at how cheap cylinder and piston kits are as well as new cranks. I am mechanically inclined so rebuilds would be a lazy day task...thoughts please...sorry for the redundant topic.

 

[redprospector]

When milling, or cutting "big timber" the part that gets the most wear is the operator.
You would have to weigh it out. I don't mill with a chain saw, but the bigger saw would give you more speed in the cut on big logs. How important is production?
When I was falling for the mill here we were cutting enough big trees I carried a 2100xp. As the trees they marked got smaller I went to a 288xp, then to a 371 and 044. I cut with a 372, and a 7900 now (I know, same as 371, and 044). I can still cut the ocasional big tree, just not as fast.

Andy

 

[joesawer]

When milling, or cutting "big timber" the part that gets the most wear is the operator.
You would have to weigh it out. I don't mill with a chain saw, but the bigger saw would give you more speed in the cut on big logs. How important is production?
When I was falling for the mill here we were cutting enough big trees I carried a 2100xp. As the trees they marked got smaller I went to a 288xp, then to a 371 and 044. I cut with a 372, and a 7900 now (I know, same as 371, and 044). I can still cut the ocasional big tree, just not as fast.

Andy

+1


IMO the long constant load involved in milling with a two stroke saw is very hard on the piston, cylinder, and crank bearings. It is kind of like riding an old air cooled two stroke dirt bike on the highway. Very hard on an engine that is designed for short bursts of power.
That being said the bigger engine would cut faster so it would be under load for less time for the same production.

 

[IndyIan]

Having done a bit of milling with my 372 I would say the biggest potential for failure is the carb running lean for some reason and then a problem with the cooling system, dirty fins or partially clogged vents. I guess they would cause piston scoring and then seizure....

I assume that the cooling systems for all pro saw are designed for the saws to run at full throttle constantly through a whole tank of gas. It sounds like something an engineer would design too anyways

I run my saw a bit rich and 40:1 with good oil so I don't worry about my occaisional milling.
Ian

 

[ShoerFast]

Yet another .02 cents by the shoer

Andy , Lakeside dose a lot of milling, and mentions that a 660 is not designed to run full-cant cuts, there designed to cut hard in a round, then cool.

From the hip, if a person was doing that much milling that there wareing out saws, they would opt the bigest saw engine they could and detune it a little, (smaller carb?) time is money at a point.

 

[fishhuntcutwood]

+1


IMO the long constant load involved in milling with a two stroke saw is very hard on the piston, cylinder, and crank bearings. It is kind of like riding an old air cooled two stroke dirt bike on the highway. Very hard on an engine that is designed for short bursts of power.
That being said the bigger engine would cut faster so it would be under load for less time for the same production.

+1 again.

Piston rings are meant to wear. That's why you can change them so easily. Bars wear, but they'll wear anywhere you cut with them.

 

[Lakeside53]

I assume that the cooling systems for all pro saw are designed for the saws to run at full throttle constantly through a whole tank of gas. It sounds like something an engineer would design too anyways

Actually, they are not... which is why richening up the mixture to detune (reduce HP) the saw is really important when milling. Saw are designed for intermittent power - i.e. crosscutting

 

[Nik_Danger]

Actually, they are not... which is why richening up the mixture to detune (reduce HP) the saw is really important when milling. Saw are designed for intermittent power - i.e. crosscutting

when you say make the mixture more rich are you talking about adjusting the carb or adding more oil to the gas mix...sorry if that sounds noob-ish but its hard to discern from your post. I've never heard of that before so I would really appreciate it if you could fill me in. Thanks man!

 

[aquan8tor]

Richening up the carburetor jets. you want more fuel, less air--when the carb runs lean, the rpms race up, giving a boost in power, but a boost in heat as well. Its also a good idea to richen up the gas/oil mix as well-- I run about 40:1 instead of the "normal" 50:1.

 

[Nik_Danger]

ahh I see... thanks dude! I can see how that would lessen the load.

 

[Crofter]

Actually, they are not... which is why richening up the mixture to detune (reduce HP) the saw is really important when milling. Saw are designed for intermittent power - i.e. crosscutting

Lakeside, can you think of any engine modifications to a saw that would make it better for milling? Other than Muffler. If you detune and have it run cooler by richening the mixture for milling it would seem counterproductive to do mods that would increase output and therefore more load on cooling ability.

 

[Lakeside53]

Not my expertise.. but you're right - modding for more power is counter productive in most milling applications simply because I don't think there is any great thermal reserve in any modern saw. Opening up the muffler to overcome excessive restriction is good, but again more power is more heat. The question is whether you are getting rid of more then you are contributing, and where.

Bottom line it's all about cooling, but not just via external fins, but the piston top edge temperature at the exhaust port. The 066/660 runs very close to the edge already. I see many with severe ablation.


To answer Nik..

I richen the mixture (H jet adjustment) AND richen up the mix ratio. My 066 has a dual port muffler, and is set to 11,500 ->12k wot (typically the lower end), and 40:1 +/- full synthetic. For cross cut it's 12,500 to 13,000, 50:1 full synthetic. It's a bit more complicated on my 088 as it has a rev limiting coil, but it definitely set way rich!

 

[joesawer]

IMO opening up the muffler, and making the exhaust port more efficient lets more heat out of the engine in the exhaust instead of being absorbed into the piston and cylinder.

 

[Lakeside53]

Yes, BUT it lets the engine make more power, and as it's not a 100% efficient device, you make more heat... question is are you removing it faster than a stock engine?... and that problem with the piston surface heat.

 

[rreidnauer]

IMO opening up the muffler, and making the exhaust port more efficient lets more heat out of the engine in the exhaust instead of being absorbed into the piston and cylinder.

Yes, BUT it lets the engine make more power, and as it's not a 100% efficient device, you make more heat... question is are you removing it faster than a stock engine?... and that problem with the piston surface heat.

That's one of the reasons I'd like to get the 3120 woods port job. Free it up, but run it fat to maintain it's original HP, and hopefully keep it cooler. The problem is, I haven't figured a way around the fixed HS jet yet. Is there an adjustable HS version of the Walbro WG 8?

 

[joesawer]

Yes, BUT it lets the engine make more power, and as it's not a 100% efficient device, you make more heat... question is are you removing it faster than a stock engine?... and that problem with the piston surface heat.

The combustion temp is not directly tied to power. If the compression is not raised and the fuel mixture is not any leaner the combustion temp should not go up. The result of getting the exhaust out of the system more rapidly should reduce the heat absorbed by them keeping them cooler allowing them to be a better heat sink for the exhaust edge of the piston. The result of more cool air and fuel traveling under the piston should help also.

Most woods ports involve raising the compression and the exhaust port. Both of wich I think are not good for a milling saw. Raising the compression increases the combustion temp, raising the exhaust port might be harder on the edge of the piston as it begins to open.

 

[Crofter]

The combustion temp is not directly tied to power. If the compression is not raised and the fuel mixture is not any leaner the combustion temp should not go up. The result of getting the exhaust out of the system more rapidly should reduce the heat absorbed by them keeping them cooler allowing them to be a better heat sink for the exhaust edge of the piston. The result of more cool air and fuel traveling under the piston should help also.

Most woods ports involve raising the compression and the exhaust port. Both of wich I think are not good for a milling saw. Raising the compression increases the combustion temp, raising the exhaust port might be harder on the edge of the piston as it begins to open.

The first paragraph of your post is what I think you get from removing muffler restriction and the retained heat in the muffler and exhaust flange area. It will increase fuel consumption as more is lost out the exhaust and this should enhance the evaporative cooling and lubrication effect. I am sure that is a plus for milling.

Your description of the "woods port" is probably pretty typical scenario. It gets the exhaust out sooner too, but does so while it is earlier in its burn cycle so is much hotter. It also sacrifices part of the power stroke, so to regain or increase the output horsepower, more fuel must be burned more intensely and at a higher RPM. The torque curve will be more peaked and higher. It makes for an excellent limbing saw and sure will cut faster in timed cuts but it may be exactly the opposite of what you need for a milling saw that has to be fed heavy and continuously for long periods. What is usually done in the way of enlarging ports reduces piston bearing and sealing area in the cylinder. Again not conducive to long life under sustained heavy load.

Having a saw modified that will make timed cuts faster than a stock saw of nearly twice the size is sure a heck of a rush and it is addictive I think; It is easy to forget (or deny) that there are real tradeoffs that need considering at times.

 

[rreidnauer]

The first paragraph of your post is what I think you get from removing muffler restriction and the retained heat in the muffler and exhaust flange area. It will increase fuel consumption as more is lost out the exhaust and this should enhance the evaporative cooling and lubrication effect. I am sure that is a plus for milling.

Your description of the "woods port" is probably pretty typical scenario. It gets the exhaust out sooner too, but does so while it is earlier in its burn cycle so is much hotter. It also sacrifices part of the power stroke, so to regain or increase the output horsepower, more fuel must be burned more intensely and at a higher RPM. The torque curve will be more peaked and higher. It makes for an excellent limbing saw and sure will cut faster in timed cuts but it may be exactly the opposite of what you need for a milling saw that has to be fed heavy and continuously for long periods. What is usually done in the way of enlarging ports reduces piston bearing and sealing area in the cylinder. Again not conducive to long life under sustained heavy load.

Having a saw modified that will make timed cuts faster than a stock saw of nearly twice the size is sure a heck of a rush and it is addictive I think; It is easy to forget (or deny) that there are real tradeoffs that need considering at times.

Thanks for the info. Saves me a few bucks there. So it's gonna be a modded muff and carb then.