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Both 200 and 201T's Fatal Design Flaw

Jomo

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Placing the muffler directly under the cylinder the entire length of the cylinder!

Hot air rises straight up into the cylinder's cooling fins.

Why they quit placing 020T mufflers on the right rear side's a mystery to me......

My 020AVE has never rattled a muffler loose or overheated during serious removals.

I'll never by another 201 until they regain their senses.

Jomo
 

Bart

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Another view is that they have shroud forced air cooling on the muffler too, say, unlike a typical MS260 etc open air style muffler (?). Could have partly been the plan aside from protecting operator from contact burns. Just speculating.

I think the mufflers have all stayed still on my 200T's. Can't contribute any info on the overheating IME. Maybe I got close a few times. Any one else's experiences?

I do have an SH55 that likes to spit forth it's muffler screws periodically at inopportune times. Usually cold end of the day darkness coming.
 

Jomo

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Keeping that cylinder as cool as possible's the exact reason every two stroke dirtbike mfr started water cooling their bikes in the early eighties.....

It's just not logical to place a hot muffler below and along the entire cylinder's length, doing so only results in the cylinder being heated along the bottom and both sides. The only side of the cylinder not being heated by the muffler's the top.

Not cool man......

Jomo
 

Nutball

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Husqvarna t540 II has the exhaust blow on the cylinder fins. I rotated the exhaust deflector on a 10hp brigges engine once because it was aimed right at the valve cover. We put lots of hours on it that way.

DSC04726 (1024x768).jpg DSC04727 (1024x768).jpg
 

Jomo

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Consider this thread just a word of warning for those of you willing to pay a grand for an MS200T.

If you use them as hard as I did?

This is the result.



Don't get me wrong, I think it's the greatest removal top handled trimsaw ever made.

But it was far from bullet-proof, the 020AVE came closest.

The last magnesium cased 020 of the line, with right side rear exhaust......

Jomo
 

Bart

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When you consider water vs air cooled, try to envision the air flow on the fins as if it was water, and envision the uniformity of flow at all places at all fins and also that if the air passed a fin on the way there it's starting out as "hot coolant" and note how in the h_ll are you supposed to get flow on the air exit side's fins - then you go "damn I'm glad I didn't have to design that SOB". Then take water, where you can flow it any old which way you want, in or out of the base, cylinder side or head and the thermal heat capacity of the water is easier to manage in conjunction with flow rate than the myriad of varying thickness air cooling fins with inherent problems of (pre)heated airflow, and proximity to the burn. Then you go, ok, water's gonna work better. And it does. They went to tighter engine tolerances to go with the more uniform engine temp.

A professor once set me/us straight on that heat exchanger design was non trivial even just for same flow vs cross flow. We just nodded our heads, remaining no smarter than before. Now there's CFD programs for the physics but the vagueness of 2 stroke jetting and loading messes things up. I remember the onset of water-cooled dirt bikes. I had a YZ125 with the rad on the bars where the number plate should be. I bet air cooled engine design is nearly a lost art probably based now on old established designs. I once tried to figure out the performance of a cpu chip to heatsink to air to receiver fins thru metal to external passive convective fins. I kind of got it but it basically beat me and confounded me, I never got a confident answer to it. But I did learn that in convective cooling airflow is king and hence various shrouding designs abound. Shrouding can use airflow to compensate a lot. Just look at your lawn mower or a vw engine. The temperature increase of the air on it's way by is pretty small compered to the metal surface temperatures and I think that's the secret. Imagine a car in Death Valley and you could say there's hot, and then there's hot, how in the heck is my rad still getting it done with 120 degree air blowing on it? Well that's a bit different, tons of fin area on a lower temperature differential. I've poked a can of worms.... get back in there!

Sorry if I bored anyone.

Yeah, housebound again :)
 

Magnus

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No, There is a fan that should create the air flow to cool fins and blow out there.
So you have a flow of air and posetive air pressure around cylinder. Not much radiant heat unless you run it too hot and turn it off instead of cooling it. Heat from muffler does't affect as the air go thru fins first. It actually cool muffler a bit.

Bigger problem is the ones chasing rpm's and run them lean, too hot.
Same thing with those that run them a bit hard.

Cooling is best don flipping throttle so you get rpm up and down, a lot of airflow and fuel air mix thru it without load.
NOT idle or stop...
 

Magnus

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Dirty fins do more harm then were ever you place muffler as they quickly reduce cooling by 25%.
Really dirty, 50%.
Had several saws here that caught fire due to oil and dust in fins...

It is not uncommon saws are run a bit too hard and get a bit hot. More common than most know.
So to cool them off is a good thing to learn.
Saws today run hotter and hotter even under no load so emissions get good.
15 years ago a saw of today would get up on bench and get a workover to find airleak or try to get more fuel.
 

Magnus

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Some years ago I talked to an engineer designing saws at Husqvarna about this and it is even cooling that is the larger problem on saws.
Most heat is at one side of cylinder, by exoust and towards the top.
This happen to be the place furhest from fan too most often and fins are used to not just guide airflow, but also transport heat.
Getting an even cooling is very hard and one of the challenges they face in the hunt of better emissions.
They have tried liquid cooling in closed circuits in Partner factory in mid 70's. It was efficient and did the trick, but got too expencive and heavy. Now when fresh air cylinder weigh 35% more it is even more important to chase grams...
 

Marc-Antoine

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Consider this thread just a word of warning for those of you willing to pay a grand for an MS200T.

If you use them as hard as I did?

This is the result.
......

Jomo
What I found strange is to cast the 200T's mufler in aluminum. Both casting and aluminum aren't the best suited for a very hot and hard vibrating part.
Good point that they went to stamped stainles steel for the 201T.
 

Magnus

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Materials and heat is often the reason they use same material in muffler as cylinder, but it does not work as intended, I think.
If gasket is ok, screws not over tightened, it works OK..
But I see your point.
I think it is better with tin. Must be cheaper if nothing else.
 

Jomo

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Well yesterday I was working a Stone pine with a fair sized leader, 14 inch, that had split and hung up in lower branches.

So I pieced it out with a new handsaw, back to fair sized wood about 4 inches. Thinking my new 201 could handle it from there.

But the dang thing started overheating again after just a few cuts. Completely disgusted, I called it a day, went back to my shed, cleaned up n sharpened my 30 year old magnesium cased 020 AVE.

Went back this morning and was quite pleased with how easily n effortlessly that old 020 made mince meat out of that leader without breakn a sweat. Gave me confidence I could've cut the whole dang tree down into firewood without any problem.

30 years old n makin the 201 look exactly like the pile of ill engineered junk it is.

Anyone want a new 201 cheap?

Say 400.00 bucks?

Jomo
 

lxskllr

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How can you tell it's overheating? Sounds like you have some problem with that saw that isn't inherent in the design. If I'm reading right, it failed on 4" wood? Anything should cut that.
 

Jomo

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It does fine until six inch wood, at which point it starts missin n smokin .

Even the owner of my local Stihl dealership's acutely aware of the 201 overheating's a widespread problem that's causin him lots of problems here locally.

Jomo
 

Nutball

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it starts missin n smokin
Too rich, must be a carb issue if M tronic, or the air filter is clogged, possibly with oil if it isn't sawdust, or the weather is too hot, but that is unlikely.

I guess it could tune itself way too rich if it thinks the engine is overheating. They use either spark plug resistance or a temp sensor in the carb.
 

treebogan

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I think the Mufflers come loose because the Aluminium head and the steel screws have different expansion rates when hot.The head on a climbing saw weighs next to nothing,I bet those holes the bolts in it expand quite alot when the saw heats up.
 

Altissimus

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When you consider water vs air cooled, try to envision the air flow on the fins as if it was water, and envision the uniformity of flow at all places at all fins and also that if the air passed a fin on the way there it's starting out as "hot coolant" and note how in the h_ll are you supposed to get flow on the air exit side's fins - then you go "damn I'm glad I didn't have to design that SOB". Then take water, where you can flow it any old which way you want, in or out of the base, cylinder side or head and the thermal heat capacity of the water is easier to manage in conjunction with flow rate than the myriad of varying thickness air cooling fins with inherent problems of (pre)heated airflow, and proximity to the burn. Then you go, ok, water's gonna work better. And it does. They went to tighter engine tolerances to go with the more uniform engine temp.

A professor once set me/us straight on that heat exchanger design was non trivial even just for same flow vs cross flow. We just nodded our heads, remaining no smarter than before. Now there's CFD programs for the physics but the vagueness of 2 stroke jetting and loading messes things up. I remember the onset of water-cooled dirt bikes. I had a YZ125 with the rad on the bars where the number plate should be. I bet air cooled engine design is nearly a lost art probably based now on old established designs. I once tried to figure out the performance of a cpu chip to heatsink to air to receiver fins thru metal to external passive convective fins. I kind of got it but it basically beat me and confounded me, I never got a confident answer to it. But I did learn that in convective cooling airflow is king and hence various shrouding designs abound. Shrouding can use airflow to compensate a lot. Just look at your lawn mower or a vw engine. The temperature increase of the air on it's way by is pretty small compered to the metal surface temperatures and I think that's the secret. Imagine a car in Death Valley and you could say there's hot, and then there's hot, how in the heck is my rad still getting it done with 120 degree air blowing on it? Well that's a bit different, tons of fin area on a lower temperature differential. I've poked a can of worms.... get back in there!

Sorry if I bored anyone.

Yeah, housebound again :)
... Thank goodnesses you mentioned Volkswagen !!! , The proof is the #3 Cylinder burning out (Valves or worser) in numbers above all the other Cylinder s ... Airflow
 
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