Stihl MS391 saw, 11 months old, 'dropped' its muffler

MikoDel

New member
Location
SE PA
Thought this worth mentioning, the MS391 I purchased in Nov 2020 'shook off' its muffler the other day. I saw that the muffler was coming loose, eventually developing a nasty case of the hippie-hippie shakes.


Eventually it just dropped off in the middle of a job. Kept using it until the cutting was done - had to. Don't have another saw big enough to do that work. Of course I screwed my earplugs in so deep they touched my brain.

So my local dealer ordered the new muffler. I thought that PERHAPS I might be able to use the saw in the meantime, but no way. The heat is starting to melt the frame.

And AREN'T I SURPRISED to learn that Stihl's warranty on MS chainsaws is only 3 months. Sheesh. I had my old MS310 for over a decade. Nothing ever 'fell off' that! (Edit - warranty IS one year, if my dealer is OK saying it's a home use scenario.)

I'm not an animal w/my equipment. I always try to let the saw do the work... just feel how fast it wants to cut, and go w/the flow. But Stihl positions the muffler right in front, so sure, once in awhile there's no doubt that the muffler takes maybe a tiny bit of the brunt of the saw when it's pressed up against the wood. And then the vibration just totally opened those mounting holes right up. I like the saw a lot. But I don't like this nonsense.

Now that I know how easy it is to mount up (just take the plugs out of the front of the and bolt it up w/a torx bit) I'll do the re-fit myself. Not gonna pay the dealer cause he takes too long to turn around equipment. And like I said, it's NOT under warranty.

Ahhh, goodness gracious.
 

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Jehinten

Carpal tunnel level member
Location
Evansville
Interesting, I have a 391 that is about 10 years old. It's been dropped and ran over but the muffler has never fallen off. Just recently took it off of my work truck and replaced it with a modded 261, then went through and fixed all the little things that were wrong with the 391. Still a good running saw after 10 years.


I suspect the muffler being loose and missing during use may have done more damage than just melting plastic. The lack of back pressure should have thrown your carb adjustments out of whack. Not sure if it would have made you run rich or lean.
 

MikoDel

New member
Location
SE PA
I suspect the muffler being loose and missing during use may have done more damage than just melting plastic.
Oh God I certainly hope not!! It Stihl ran pretty darn good while I was cutting after it fell off. A bit of stuttering under full throttle when cutting light, but OK under normal load. I'm glad to know you did not have this issue with your saw. I am going to be MUCH more careful about NOT contacting the muffler face to the tree. I surmise that I may have torqued it against the wood a few times, and that's what weakened the mounting enough to allow the vibration to run away and destroy it. It's too easy to involve the muffler against the tree.
 

Tom Dunlap

Here from the beginning
Administrator
I suspect the muffler being loose and missing during use may have done more damage than just melting plastic.

There is a FINE LINE betwixt RANT and WHINE...

Given very limited info to make a CSI it sure looks like the muffler was bumped more than you're admitting. You may not notice every time the saw gets pulled into the cut and whomps the muffler. Metal doesn't bend and rip like that from rare bumps.

In 45+ years of running saws I never had a muffler fail like that in an instant. IF a muffler was breaking or the studs loosening I had plenty of warning to stop and do a repair before the metal failed.

Does the saw have cutting dogs on the front? You should see if you can find some that fit that are longer. This will keep the muffler further away from more whomping
 

Reach

Been here a while
Location
Atglen, PA
In my 18 years running saws, I’ve had one muffler fail, on an old 192T. I am curious if the fact that the 391 is not a Pro saw, but rather a midrange model makes any difference in the durability of the muffler, but regardless, I do not believe that muffler failed all at once. Based on the pictures, it looks like that muffler has been failing for quite some time, and just chose that time to finally fall off.

Also, the heat damage likely occurred, at least in part, while the muffler was loose, not after it fell off. Once it dropped off the exhaust would flow more or less straight out, when it was leaking it would have been directed towards the side of the saw where it is damaged.
 

chipper1

New member
Location
Grand Rapids
Nothing went wrong with the muffler.
When things loosen up, they need to be tightened. The reason the holes are all wollowed out is because it wasn't tightened as soon as it came loose.

Pro saws are built stronger and have more power per pound, and they handle better as well. That being said, if something loosens up it will still have to be tightened.
A little blue loctite goes a long way ;).

Pretty sure the 391 and the 311 share the same muffler if you need one again.

Hope you get it all taken care of soon.
 
Last edited:

MikoDel

New member
Location
SE PA
Well, I appreciate more of you weighing in. There's a LOT more to this now.

Current status:
*Had to buy a new 391 saw
*11 month old MS391 now needs helicoils, another new muffler (3rd one), plate, & screws. Stihl won't warranty anything because my ex-dealer told them there are signs of abuse.
*My NEW Stihl dealer (YAAAAYYYY!!!!) did say the mufflers come loose a lot, especially on the concrete cutters. Helicoils are a common fix in their shop.

more...
The first time the muffler fell off, the 5X16mm screws remained in the cylinder. They didn't come loose @ all. I agree the distortion of the metal, at the very start, must have been from unintentional contact w/the tree.. But the way it became really grossly distorted... that's totally from vibration. I didn't know how to tighten it. The stock muffler has metal clips over the holes where the screws are. The replacment muffler from Stihl does not. Of COURSE I noticed the muffler shaking loose that day, but I had no idea what to do about it. It was far too hot to try & remove those metal clips, even if I had known there were screws under there.

Trees are irregular, and saw dogs, no matter how big, can't prevent a burl, big knot or branch stump from sometimes pressing against a forward facing muffler. I never owned a saw where I had to continually mind the front. Now that I know, I'll CERTAINLY be more careful in the future.

Now here's some craziness... my FORMER Stihl dealer (David Lightkep, real noodniks they are over there) told me, 'We can't give you the parts under warranty. Dealer has to do the install, otherwise it won't be warranty.' Fine, I said. When I got the saw back a few hours later, I got something else as well: a bill for $99. "Excuse me, this is a warranty job," I explained to the cashier. The owner Adam came out, 'This isn't warranty, this is normal wear and tear.'

OK so now my head's spinning a little... I got charged for parts, and labor, for a repair that I was told would be warranty.
'But you said this was all warranty!' I said, somewhat incredulously.
Adam said, 'I do a lot of these mufflers, they fall off all the time.'
'What if I call Stihl? Can I try to get it warrantied?' I asked.
'I don't have time to get on the phone w/Stihl and get this approved,' he said, which wasn't even a relevant response, really. and there's NO attempt by Lightkep whatsoever to try and placate me. They just don't care!

But ya know, he turned it around the day the muffler came in, which I needed, so I paid the bill, even tipped him $20, and went on my way. I sharpened the chain before I used it again, and it's a damn good thing I did, cause the guide bar nuts weren't even finger tight. God help me, had I took that written receipt "repaired and tested" @ face value, and starting cutting straightaway, that chain would've flown off and possibly done me plenty of harm.

So next day I'm on the jobsite, and 5 mins into cutting, the muffler shakes loose w/the screws, and the screws are lost. I went back to Noodnik's Inc, and luckily they had the screws in stock. While there I explained, not only did the thing come loose in 5 mins, but the guide bar nuts were dangerously loose. I got a refund for the labor, and the owner, adam, also told me some parting wisdom, "I can't continue to do business this way if you're going to question my repairs." No "We're really sorry, Miko..."!!! Ha ha ok, I'm not going to go blow-by-blow what was said @ that point, but I certainly assured him I am not a liar, and I wouldn't be back here if I didn't have to be.

So now I'm cutting, checking tightness, cutting, checking...
at this point I know what to listen for, so I kept an eye and an ear out for problems while working. and maybe two days later, both mounting holes are stripped, and the saw cannot be used.

Now in response to the comment about "the heat damage occured while the muff was loose, not after it fell away." There's no way I am gonna chance that. Of course I'd like to continue to use it muff-less, if I could. But if I seriously warp the chassis then I'm really eff'd. Plus the exhaust is too hot to even hold it while revved up w/out the muff. I think after awhile it might even burn thru gloves. and as for david lightkep, thanks for telling the mfgr the saw was subject to misuse/abuse, cause Stihl is washing their hands of everything. They know the cyl head is now stripped and has to be helicoiled.
 

MikoDel

New member
Location
SE PA
You should see if you can find some that fit that are longer. This will keep the muffler further away from more whomping
Great idea on paper, but given the fact that the 25" bar is the largest saw I own, I really need to get max depth of cut as possible. But I WILL be more careful of whomping inna future.
 

MikoDel

New member
Location
SE PA
Nothing went wrong with the muffler.
When things loosen up, they need to be tightened. The reason the holes are all wollowed out is because it wasn't tightened as soon as it came loose.

Pro saws are built stronger and have more power per pound, and they handle better as well. That being said, if something loosens up it will still have to be tightened.
A little blue loctite goes a long way ;).

Pretty sure the 391 and the 311 share the same muffler if you need one again.

Hope you get it all taken care of soon.
Stihl's Loctite on their factory issued 5X16mm torx screws is grey in color. Hmmmm... also one of my best buds is an ace mechanic, and he told me that heat is the way he breaks frozen screws when Loctite is been used. He's not very confident that's the answer in an exhaust application. I suggested some kind of lockwasher perhaps.

The next saw up (pro saw) is the MS462. While some of you have commented in another thread that the 462 is the better professional saw, it's also double the price. Up until this muffy mess, I was loving my MS391
 

climbstihl

Branched out member
Location
Germany
Stihl's Loctite on their factory issued 5X16mm torx screws is grey in color. Hmmmm... also one of my best buds is an ace mechanic, and he told me that heat is the way he breaks frozen screws when Loctite is been used. He's not very confident that's the answer in an exhaust application. I suggested some kind of lockwasher perhaps.

The next saw up (pro saw) is the MS462. While some of you have commented in another thread that the 462 is the better professional saw, it's also double the price. Up until this muffy mess, I was loving my MS391
The next saw up would be the MS400C, not the MS462. The 400 ist a great saw, both spec wise, and in use. And from what I can see online, it should be about 300$ less than the 462. Looking at US saw prices makes me sad, compared to Germany... But at least we get new saws first
 

MikoDel

New member
Location
SE PA
The next saw up would be the MS400C, not the MS462. The 400 ist a great saw, both spec wise, and in use. And from what I can see online, it should be about 300$ less than the 462. Looking at US saw prices makes me sad, compared to Germany... But at least we get new saws first
You R correct - I did kno that. I guess I didn't feel like expounding upon, what I meant was, 462 is the next saw up w/a significant displacement difference. I don't care if 400C piston is mag, titanium unobtanium or enriched uranium, LOL. I'm not about to pay $300 for 2 cc more motor and M-TRONIC.

and speaking of US and new saws first, I gotta admit I'm happily surprised I've been able to get these parts for my MS391, and even a new 391 for that matter. I spoke to my former boss today, and he relayed that Moyer, a huge power equipment dealer in our area, was denied their ENTIRE shipment of like, 300 Ariens snow throwers for this winter's stock. There simply is no stock, says ariens. Damn! My heart goes out to them.
 

Dan Cobb

Branched out member
Location
Hoover
Well, I appreciate more of you weighing in. There's a LOT more to this now.

Current status:
*Had to buy a new 391 saw
If I buy something that turns out to be a lemon (appliance, electronic, tool,...), the last thing I do is buy another of the exact same thing. I normally change manufacturers as well. Maybe that's just me.
 

chipper1

New member
Location
Grand Rapids
Stihl's Loctite on their factory issued 5X16mm torx screws is grey in color. Hmmmm... also one of my best buds is an ace mechanic, and he told me that heat is the way he breaks frozen screws when Loctite is been used. He's not very confident that's the answer in an exhaust application. I suggested some kind of lockwasher perhaps.

The next saw up (pro saw) is the MS462. While some of you have commented in another thread that the 462 is the better professional saw, it's also double the price. Up until this muffy mess, I was loving my MS391
Ask your friend what he uses when he installs an insert in a spark plug hole that has been stripped out.
I've helped many with problems, lots with saw problems, but people have to actually take the advice and apply it for it to work.
You've been given much advice, but it seems more like you just want someone to side with you. Unfortunately a new dealer won't fix this nor will a new saw, but hopefully things will change.
Have a blessed week.
 

climbstihl

Branched out member
Location
Germany
You R correct - I did kno that. I guess I didn't feel like expounding upon, what I meant was, 462 is the next saw up w/a significant displacement difference. I don't care if 400C piston is mag, titanium unobtanium or enriched uranium, LOL. I'm not about to pay $300 for 2 cc more motor and M-TRONIC.

and speaking of US and new saws first, I gotta admit I'm happily surprised I've been able to get these parts for my MS391, and even a new 391 for that matter. I spoke to my former boss today, and he relayed that Moyer, a huge power equipment dealer in our area, was denied their ENTIRE shipment of like, 300 Ariens snow throwers for this winter's stock. There simply is no stock, says ariens. Damn! My heart goes out to them.
I get where you're coming from, but to me 300$ more for 0.9 hp more, with 400g less weight, ist definitely worth it. That's not even taking into account the better construction of a pro saw.
 

Barc Buster

Branched out member
You R correct - I did kno that. I guess I didn't feel like expounding upon, what I meant was, 462 is the next saw up w/a significant displacement difference. I don't care if 400C piston is mag, titanium unobtanium or enriched uranium, LOL. I'm not about to pay $300 for 2 cc more motor and M-TRONIC.

and speaking of US and new saws first, I gotta admit I'm happily surprised I've been able to get these parts for my MS391, and even a new 391 for that matter. I spoke to my former boss today, and he relayed that Moyer, a huge power equipment dealer in our area, was denied their ENTIRE shipment of like, 300 Ariens snow throwers for this winter's stock. There simply is no stock, says ariens. Damn! My heart goes out to them.
You are missing the main point/s of the difference between a pro saw and a farm/homeowner saw. Take a closer look at the numbers and you’ll see the main advantages of the 400 over the 390. Also maybe look into some basic chainsaw maintenance information. It’s just like with trees the more you know the more you grow.
 

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