# Two stroke engine life : saws vs dirtbikes



## Up and coming

What's up everyone I was driving to the jobsite the other day when me and our operator were talking about our fondness of everything 2 stroke, mainly dirt bikes and saws. the conversation eventually lead into maintenance intervals for our bikes and how we can't seem to get more than 8 months out of a ring and piston on a bike that we only ride on the weekends. However we have saws that have been run wide open all day 5 days a week for years with no signs of giving up anytime soon (my 200t). So in conclusion, my question,
why do saws last longer than bikes or should stihl just start making bikes (stihl if your reading this you definitely should. I'm sure I speak for everyone in saying we would all buy one)


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## sean donato

That's kinda a loaded question. Depends on the bike and use. Can't say I ever had to do a ring job every year on a bike when we rode. The last bike we had was a kz250 had a years on that engine, just trail riding. Bit of light mx at times nothing super punishing.


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## ATpro

When we ran motocross we would rebuild every race of two. Keeping them in the power band all day would wear a set of rings out in no time. My dirt Bikes would last a year or more without a ring job depending on how much you ran it. The idea on rebuilds was a preventive rebuild before any damage happened. With chainsaws we just ran the heck out of them till they quit which could be years at the rate we ran them.


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## Ted Jenkins

ATpro said:


> When we ran motocross we would rebuild every race of two. Keeping them in the power band all day would wear a set of rings out in no time. My dirt Bikes would last a year or more without a ring job depending on how much you ran it. The idea on rebuilds was a preventive rebuild before any damage happened. With chainsaws we just ran the heck out of them till they quit which could be years at the rate we ran them.


My bikes got a complete overhauls every twenty five to fifty hours of operation. Suspension components could go from ten to a hundred hours. Every single practice or race had to be logged and taken care of. When you are already risking life and limb maintenance can not be over looked. Always some thing showed up that needed to be replaced. If you were riding just SuperX then a tear down every twenty hours. My chain saws which are very low performers can go through a hundred cords and still run great. Dirt bike motors produce from 60 to 80 HP my saws produce maybe 10 HP. Thanks


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## weimedog

Depends on the bike and what it's life is. I'm an old fart, ran Bultaco's in the early 1970's and raced all the way to 2001, also had stints on Suzuki ( early TM's , then late 80's RM's) CZ, Ossa, Maico, KTM's, then Kawasaki's & Honda's. Had some goofy stuff like a year on Cagiva 200's in the 250 class which eventually turned into Husqvarna. ( Long Story ). My Air cooled 125's needed rings and clutches every couple of races. Sometimes would go half a season when I was a novice/armature class racer. I remember the first KTM 420 (1978) went a season without Anything required except tires, chains, sprockets and SPOKES. Motor was rugged. 1977 Maico waisted ignitions and rear wheel hubs. By the mid 1980's the water cooled Honda's would last. 250's most of a season , 125's just cleaning exhaust and rings. Point? Can't make a "blanket" statement. Motocross ... the "practice" and training was where the time was compiled. I ran a 1982 Husqvarna xc430 in AHMRA races in the 99-2000 time frame and it didn't need a thing other than wear items like tires/chains etc..and brake shoes. But the big difference is the design, dirt bikes had evolved with power valves and pipes for wider power bands. They were longer ( square vs. over square ) stroke than chain saw designs and ran at a lower RPM although the piston speed relative to the cylinder wall is roughly the same at peak RPM's. Most dirt bikes aren't run flat out under load like a saw....although I could argue 125 expert class in the late 1970's was flat out continuously for the race time, also were air cooled therefore more like a saw in application. But point is different design parameters, bikes had more weight and space latitude. And I've said for years the 800lbs gorilla in ALL these little motors is the ability to rid the excess heat. THAT more than any other parameter is why saw motors are relatively low horse power designs. They make enough power for the job at a light enough weight, which is ANOTHER thing. The "mass" and surface area of the cases are effectively a part of the cooling system on saws. Start adding horsepower without a balance of cooling systems and u have a impractical for work design. And cooling systems add weight, complexity therefore cost , and size to the package. Take a design where the cooling system is meant to be "stable" at 5hp and turn it into a 20hp motor...it will run. Even at full load, just not long enough to do a typical tree job before heat "limits" the fun.


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## rocketnorton

bikes can have a load on motor @ hi rpm w/throttle shut [eg downhill in gear] gettin very little lube.
even with injected oil, as pump sometimes works w/throttle.


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## Ted Jenkins

weimedog said:


> Depends on the bike and what it's life is. I'm an old fart, ran Bultaco's in the early 1970's and raced all the way to 2001, also had stints on Suzuki ( early TM's , then late 80's RM's) CZ, Ossa, Maico, KTM's, then Kawasaki's & Honda's. Had some goofy stuff like a year on Cagiva 200's in the 250 class which eventually turned into Husqvarna. ( Long Story ). My Air cooled 125's needed rings and clutches every couple of races. Sometimes would go half a season when I was a novice/armature class racer. I remember the first KTM 420 (1978) went a season without Anything required except tires, chains, sprockets and SPOKES. Motor was rugged. 1977 Maico waisted ignitions and rear wheel hubs. By the mid 1980's the water cooled Honda's would last. 250's most of a season , 125's just cleaning exhaust and rings. Point? Can't make a "blanket" statement. Motocross ... the "practice" and training was where the time was compiled. I ran a 1982 Husqvarna xc430 in AHMRA races in the 99-2000 time frame and it didn't need a thing other than wear items like tires/chains etc..and brake shoes. But the big difference is the design, dirt bikes had evolved with power valves and pipes for wider power bands. They were longer ( square vs. over square ) stroke than chain saw designs and ran at a lower RPM although the piston speed relative to the cylinder wall is roughly the same at peak RPM's. Most dirt bikes aren't run flat out under load like a saw....although I could argue 125 expert class in the late 1970's was flat out continuously for the race time, also were air cooled therefore more like a saw in application. But point is different design parameters, bikes had more weight and space latitude. And I've said for years the 800lbs gorilla in ALL these little motors is the ability to rid the excess heat. THAT more than any other parameter is why saw motors are relatively low horse power designs. They make enough power for the job at a light enough weight, which is ANOTHER thing. The "mass" and surface area of the cases are effectively a part of the cooling system on saws. Start adding horsepower without a balance of cooling systems and u have a impractical for work design. And cooling systems add weight, complexity therefore cost , and size to the package. Take a design where the cooling system is meant to be "stable" at 5hp and turn it into a 20hp motor...it will run. Even at full load, just not long enough to do a typical tree job before heat "limits" the fun.


I enjoyed my days building motors just to discover next week it will have to be done again. Saws only have to achieve a reasonable output for the weight that they have to have. The older saws that I have have out performed all else. More complicated tuning and more complicated systems that comply with EPA standards are the biggest reason for lackluster performance. Thanks


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