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Originally posted by vandrv:

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Originally posted by wcb6092:
Is there no love for an Echo 590 or 620 here?

I have the Echo 620 and it is a beast. It came with a 27" bar but that was more than I generally need so I replaced it with a 24". I've had a couple of Stihl and Husquvarna chainsaws and I would rate this as the best of them.

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Originally posted by hrcjon:

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there's probably some direct or indirect treatment in other industries like racing or aviation or aerospace.

There is simply no analog of a 2stroke single cylinder air cooled piston of this size in any modern racing or aviation or aerospace application. IMO you are simply depending on Stihl's testing to guide and inform you. myself i wouldn't sweat it much as if there are issues Stihl will solve them and support you. At least in the short term.

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Originally posted by fritz:
The original Stihl 400CM does use a magnesium alloy piston, where an aluminum alloy is used by most saws. For whatever reason, Stihl's preliminary reports state that the new 400C will go back to aluminum. Could be cost, production challenges, materials sourcing, maintenance issues, or others. I know that my 400CM runs & cuts very well, with very good throttle response.

I've seen it stated that a homeowner/ranch grade saw might have a useful life of 1,000 hours. At that point, the piston & cylinder are likely toast -- metals scoring and reduced pressure. A pro level saw might have a useful life of 2,000 hours.

My oldest saw is a Stihl 310, and we've had it a little over 20 years. Lots of parts have been replaced, but my shop says the engine is in amazingly good shape. Their lead tech said might last another 10 years -- but I will likely be tired of it before then. The 310 is a ranch-grade saw. It's tough to state how many hours are on the saw. Maybe 600, or 700, or 800? Pretty amazing performance, especially since we used regular automotive gas for so many years. And of course, that's why the carb has taken it in the shorts a couple of times.

I don't track hours on the 400CM, but I suspect it's at least 150, but more likely close to 200 hours. Variable-use hours. Limbing hours are the easiest on the engine -- repeated throttle up and down, then set the saw down to idle as I move the cut limbs. Felling is pretty easy on the saw -- lots of throttle blips to control the direction of the cut. Bucking logs puts more strain on the engine, as it's full throttle for extend periods. Leveling old stumps is the hardest saw duty. The saw gets really hot, the chain smokes, and the bar often gets hot enough to show some loss of paint and/or metal darkening. When I crunched the handle while felling, my shop said after the repairs that the 400CM is in great shape. The shop manager said it's pretty obvious that this saw sees hard use, but that I take care of it.

A number of factors contribute to saw longevity:
- A sharp chain. Dull chains cut slower and bog down the engine. The engine gets hotter than it should and the clutch wears faster. I sharpen before each day, and often once or twice during the day.
- Fuel quality. This is the combination of gas and oil. Automotive gas has lots of additives that aren't the best for chainsaws. Most automotive gas has alcohol -- which in addition to the water that comes with it -- is bad for chainsaw engines. Too little oil in the fuel mix will ruin the piston faster than anything.
- Bar oiling. Under-oiled bars bog down the engine in a similar way that a dull chain does. Without enough oil, there's a lot of heat from the friction. Also, a bar is a wear part -- it must be maintained (squared and de-burred), and replaced regularly under hard use.
- Air filtration. If dust gets past the air filter, the pistol will eventually show wear. An engine starved for air -- due to a plugged air filter -- will run hotter than normal, and it will bog down. I clean my filters regularly, and knock the dust off with each tank of fuel. With my newer 261 and 400, I have small piece of lady's nylons over the air filter to reduce the number of particles that make it to the filter.
- Overall saw cleanliness. At a minimum, saws should be cleaned via an air compressor after every use. Remove the oily chips & sawdust around the clutch and everywhere else they might accumulate. I go one step further and regularly hose mine down at the car wash. One has to be careful with pressured water, as there are parts of the saw that this isn't the best practice. Ixnay water in the carb. But my shop's guys state that my saws are some of the best maintained that they get to work on.

Saws run well and last a long time if the above issues are addressed. I'm expecting an extended useful life with my 400CM.

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Originally posted by fritz:
The newer, smaller displacement, 400C is slated for introduction in 2025. I expect the original 400CM will be listed for awhile.

The newer carb electronic controls have the advantage of starting with minimal pulls, regardless of saw or atmospheric conditions.

With older saws I've experienced cold days where a saw just doesn't want to start or run smoothly. It might take a bunch of pulls to start, feathered throttle during the warmup phase to keep it from stalling, and a tendency to stall when idling. Electronics sense the saw and air conditions, and all this foolishness doesn't occur.

On warm-to-hot days most saws start easily. The challenge is when the saw cools down a little bit, but not fully to air temperature. This can be where the saw might need just a little choke to start, but too much choke may flood it. Once flooded, one might clear the flooding by turning off the saw and pulling the starter a bunch of times. If that doesn't work, then it's time to remove the plug, dry it, and start over with full choke -- as the saw is likely cold by this time. Electronics sense the saw and air conditions, and all this foolishness doesn't occur.

As I see it, the only potential issue with electronic carb controls is that it sometimes takes burning a few tanks of fuel before the saw runs at its full potential. I suspect the electronics might need to record a wide enough variety of conditions to accurately predict how to control the carb. There are a number of saws out there with electronic controls -- I don't hear of many electronics failures. There are plenty of mechanical things on a saw which can fail, especially with long-term use.

There are old timers who state that they'd never own a saw with electronics, and that's why Stihl offers some saws without them. I've used a number of saws and saw brands over the decades, and I will never buy another saw without electronic carb controls.