Stihl MS 291 burnt out after 1 hr

[treesmith]

I've had saws with a dirty brake band where the brake is ineffective at full throttle, the dirt on the band rubs against dirt on the sprocket and just slips as opposed to metal on metal and stopping. I could easily understand how a dirty brake band accidently tripped would still run and cut, it would get hot as hell too
Pine sap could do this easily

 

[tree monkey]

Sorry but this one is obviously the OP fault 100%. Look at the color of the clutch!! Operator error and abuse. I'd think the crank seals got pretty hot too.

I find the chain locks up and starts to sound dry long before you'd get that much heat. Sorry the OP simply doesn't have a clue. If the break wasn't on with the saw on high idle, he was cutting with the chain on backwards, while leaning on the saw with all his weight. I've heard these stories in person, if even half of the story is true I'd be surprised.

Not so. Look at the clutch, that doesn't just spontaneously happen, the plastic doesn't melt under normal operating temperatures. To get the results we see in the OP pics, takes stupidity, or at least severe neglect. No dealer or manufacture will cover that type of damage. I'm calling it as I see it, you don't have to agree, that's fine with me.

Never ask a question unless you're prepared to hear the answer, as you may not get the answer you wanted.

If I were the OP, I'd take this as a expensive learning experience. Move on to fixing or replacing my saw, and learning how to prevent this from happening again.

I've had saws with a dirty brake band where the brake is ineffective at full throttle, the dirt on the band rubs against dirt on the sprocket and just slips as opposed to metal on metal and stopping. I could easily understand how a dirty brake band accidently tripped would still run and cut, it would get hot as hell too
Pine sap could do this easily

I agree with all of these posts

doging the saw in with a dull chain, bogging it down, slipping the clutch, causes a lot of heat.

 

[Weesa20]

It's not my fault the plastic POS melted.

I was there, you all weren't.

I have a MS291 that needs a new piston and cylinder...I'll give you $50 for you "plastic POS"...

 

[Definitive Dave]

I have no dog in this fight, just sharing my experiences.
Another fun chain brake story. Local Sunbelt rental has 290s, 291s and 390s. I was returning a mini excavator and another contractor brought back a 390 he had just picked up and told the counter guy it wouldn't run right.
One of the mechanics grabs it and takes it in the shop, I followed him out with my safety glasses after settling up. He has it on the bench with a screwdriver in the carb raising the idle and trying to blip the saw and it just grunts with no chain movement so he turns a little more. I wave my hands at him but I am not heading into the work area and he doesn't see me. After he has the saw screaming and smoking he shuts it off. He looked over at me, they all know I am a saw nerd, he said what's wrong with it? I just said chain brake and he flipped me off and got back to retuning the saw A guy can rebuild track hoes for a living and still forget simple stuff.
Stihl rep showed us an inertia brake in action at the service day last week, he took a new 291, clicked the brake off and dropped the tip on the ground, the slight impact made it trip, as it is supposed to. A chain brake can stop a chain in a tenth of a second at full throttle but at low throttle there maybe more torque? I just know you can rev up a saw and smoke the brake band from idle on many saws.
Dave

 

[Chris-PA]

There is only one place that slippage can occur between the engine and the chain - at the clutch. So if the engine is running but the chain is not turning at engine speed than the clutch must be slipping. Since that is a friction device then some or all of the engine's output mechanical energy is being turned into heat in the clutch.

If the throttle is not at idle, the brake is on (or anything else that slows the chain) and the engine has not stalled then there is one heck of a lot of power going into that clutch. If you load the engine down enough the rpm will drop until the clutch begins to disengage, and then it will begin to heat fast. Even 1hp is 746W, which is a lot of power being dumped into that assembly, which has very little surface area or airflow over it.

 

[Rockjock]

There is only one place that slippage can occur between the engine and the chain - at the clutch. So if the engine is running but the chain is not turning at engine speed than the clutch must be slipping. Since that is a friction device then some or all of the engine's output mechanical energy is being turned into heat in the clutch.

If the throttle is not at idle, the brake is on (or anything else that slows the chain) and the engine has not stalled then there is one heck of a lot of power going into that clutch. If you load the engine down enough the rpm will drop until the clutch begins to disengage, and then it will begin to heat fast. Even 1hp is 746W, which is a lot of power being dumped into that assembly, which has very little surface area or airflow over it.

I agree with you if this was a old saw, not maintained well at all but this is a new saw, clutch and brake band in good nick. So where does slippage come into this?. If the op was to take his saw engage the chain brake from idle and depress the trigger WOT what will happen? Sound of engine bogging and chain not moving. Now OP takes the saw depresses the trigger WOT then engages the chain brake what happens? bog sound followed by chain stopping. How can the saw be run with the brake band activated?

 

[AKDoug]

I sold a 271 that came back looking like that after one day. The owner tripped the brake in a big log and though the saw was just stuck and kept horsing on it. Only about 45 seconds of that kind of abuse will result in a saw that looks just like that. It usually happens to customers that went from a POS dull saw and bought a new one, not realizing what a good saw is supposed to sound like. I wish I had a beater saw around to video and demonstrate how short of a time it takes to do this.

 

[Chris-PA]

I agree with you if this was a old saw, not maintained well at all but this is a new saw, clutch and brake band in good nick. So where does slippage come into this?. If the op was to take his saw engage the chain brake from idle and depress the trigger WOT what will happen? Sound of engine bogging and chain not moving. Now OP takes the saw depresses the trigger WOT then engages the chain brake what happens? bog sound followed by chain stopping. How can the saw be run with the brake band activated?

That the clutch got hot is proof that it was slipping. If the clutch was out of spec (weak spring, etc.) it could still get quite hot - but the chain would still be slipping.

There is no way for a chain to slow down other than clutch slip, which means heat, which should mean "stop now".

 

[AKDoug]

I have also seen guys that have taken a hot bar and set it down in the snow. Come back two hours later and it's frozen solid. They fire up the saw and horse on it trying to get the chain to move....beating the bar on a log trying to get it to move, etc. After a minute of this they can't understand why the housing around the clutch is starting to burn the paint or melt plastic. I imagine the same thing could happen with excessive amounts of pitch left in a bar overnight to dry.

 

[Rockjock]

I sold a 271 that came back looking like that after one day. The owner tripped the brake in a big log and though the saw was just stuck and kept horsing on it. Only about 45 seconds of that kind of abuse will result in a saw that looks just like that. It usually happens to customers that went from a POS dull saw and bought a new one, not realizing what a good saw is supposed to sound like. I wish I had a beater saw around to video and demonstrate how short of a time it takes to do this.

I get your point but I just can not see it. Please point out the flaw in my thinking here. I have a New saw that at WOT will stop a chain dead if the chain brake is engaged. Then I take the same saw from idle and engage the chain brake and give it the berries and the chain does not move. all this and and a person that has operated saws for a very long time lead me to believe it may be something else. I agree someone who does not know what they are doing might be able to do it. But I still do not see it.

 

[AKDoug]

That the clutch got hot is proof that it was slipping. If the clutch was out of spec (weak spring, etc.) it could still get quite hot - but the chain would still be slipping.

There is no way for a chain to slow down other than clutch slip, which means heat, which should mean "stop now".

Remember that on a chainsaw clutch, weak springs don't effect it's grip. The springs are to keep it closed until the right amount of RPM is reached.

 

[AKDoug]

I get your point but I just can not see it. Please point out the flaw in my thinking here. I have a New saw that at WOT will stop a chain dead if the chain brake is engaged. Then I take the same saw from idle and engage the chain brake and give it the berries and the chain does not move. all this and and a person that has operated saws for a very long time lead me to believe it may be something else. I agree someone who does not know what they are doing might be able to do it. But I still do not see it.

The chain doesn't move. The clutch, inside the clutch drum, is slipping and creating massive amounts of heat. The drum drives the chain, but it's not moving.

 

[west041]

There's a lot of theories getting thrown out about dull chains, chains on backwards and idiot operators. I'm not joking when I say that the saw had literally, literally, 1 running hour. If that. And it was light usage. So think of this saw as being immaculate, because it was.

And as for Andyshine77, seriously man, you have stated your opinion. I don't mind asking a question and not liking the answer. What does piss me off is people who keep on beating a dead horse when they really have no idea what they are talking about. You weren't there, and you are basing your opinion on three pictures. That's fine. That is what you think. I obviously disagree. There is nothing left for you to contribute to this thread other than further inflammatory trolling. So stop trolling my thread.

 

[AKDoug]

It's a centrifugal clutch. There is always an RPM that the clutch shoes will engage with the inside of the clutch drum and spin inside of it. Each time you throttle up with a stuck drum (chainbrake on, chains stuck in tree, chain stuck in bar, etc...) you will spin the clutch inside the drum and heat it. Like Chris says, it's a small piece of metal that has no airflow over it if the chain isn't moving. Those few seconds of clutch rubbing against the inside of the clutch drum are enough to heat it. Blip the throttle enough times and it super heats in short order.

 

[AKDoug]

There's a lot of theories getting thrown out about dull chains, chains on backwards and idiot operators. I'm not joking when I say that the saw had literally, literally, 1 running hour. If that. And it was light usage. So think of this saw as being immaculate, because it was.

And as for Andyshine77, seriously man, you have stated your opinion. I don't mind asking a question and not liking the answer. What does piss me off is people who keep on beating a dead horse when they really have no idea what they are talking about. You weren't there, and you are basing your opinion on three pictures. That's fine. That is what you think. I obviously disagree. There is nothing left for you to contribute to this thread other than further inflammatory trolling. So stop trolling my thread.

Seriously dude, there is NOTHING to warranty on this saw. The results of the damage speak for themselves. Something in the operators' control caused this. Whether it was pitch buildup, dull chain, brake application, etc... There was not a manufacturing defect. Even if that clutch bearing had exploded before the rest of the mess, it has no function once the RPM's are up enough to engage the clutch.

 

[Rockjock]

The chain doesn't move. The clutch, inside the clutch drum, is slipping and creating massive amounts of heat. The drum drives the chain, but it's not moving.

I am aware of this but my point is chain not spinning I stop what I am doing and think why is it not spinning? . The OP is not a novice. So if this was to have happened to you, a seasoned operator what would be the other cause of this failure? I agree that someone who has not run a saw could do this. But someone with some knowledge I do not see it.

 

[west041]

Thanks Brettl for the advice. I do own three used saws, two 031AVs and an 041 farm boss. They have always treated me well, but I'd rather remedy the problem with the 291 for my dad's sake then get him a used saw or give him one of mine. None of mine have chain brakes either so I don't feel comfortable giving them to someone else even though my father is more experienced than I am.

I'm not as familiar with the newer Stihl saws but I will attempt a fix if I cannot get help from Stihl.

 

[west041]

Seriously dude, there is NOTHING to warranty on this saw. The results of the damage speak for themselves. Something in the operators' control caused this. Whether it was pitch buildup, dull chain, brake application, etc... There was not a manufacturing defect. Even if that clutch bearing had exploded before the rest of the mess, it has no function once the RPM's are up enough to engage the clutch.

Seriously Doug, this opinion has also been stated. If you are in the "operator error" camp then that's fine. You might as well move along and have a party with Andyshine. It's nothing personal, we just disagree. It's not going to stop me from trying my luck with Stihl.

 

[west041]

Thank you Rockjock. The one voice of reason in this idiotic thread.

 

[west041]

Those few seconds of clutch rubbing against the inside of the clutch drum are enough to heat it. Blip the throttle enough times and it super heats in short order.

I'm not disagreeing with your logic here. I'm just saying that this is not what happened. Did I mention the chain was moving?