MS291 Muffler help... won't stay on

[Jorswift]

Hey guys, new to to posting, but been reading for a while. I have a MS291 where the muffler got buggered up. Had to replace, but now the darn thing wont stay on. I have tried high temp exhaust gasket material on threads, high temp red loctite, star washers and lock washers and even just had it retapped for longer and bigger bolts. The last time, it held for a few hours, then rattles its way loose. Any ideas here?

Also, since the muffler keeps coming off, i am thinking about modding it. But how do I access the H/L screws? Thanks.

 

[Goofaroo]

Hey guys, new to to posting, but been reading for a while. I have a MS291 where the muffler got buggered up. Had to replace, but now the darn thing wont stay on. I have tried high temp exhaust gasket material on threads, high temp red loctite, star washers and lock washers and even just had it retapped for longer and bigger bolts. The last time, it held for a few hours, then rattles its way loose. Any ideas here?

Also, since the muffler keeps coming off, i am thinking about modding it. But how do I access the H/L screws? Thanks.

It’s one of a few Stihl models that have this problem. I’ve had a few come through my shop and tried all sorts of loctite and no joy. The muffler falls off within a few minutes.
I went to the dealer and asked him what he does with the Stihls that the muffler falls off of. He told me he uses some sort of epoxy and it could never be removed again but that is the only way to fix it.
That didn’t sound like a glamorous enough repair to me so I found another way.
I ordered socket cap screws that were 105mm long but they only were threaded about 1/4” longer than the factory bolts. They were oversize so I drilled and tapped the cylinder to accept them. Then I ran two nuts up against the part of the bolts where the thread stops. I tightened the nuts and then rounded them off on a grinder so they would fit through the muffler. I also added a washer under the nut. Then I installed the muffler and tightened the two bolts with an Allen wrench. To be certain the muffler would never fall off again I drilled holes in the head of each bolt and safety wired them together.

It’s a lot of work just to keep a muffler on but it was the only way I could think of. I ordered 10 of those bolts and still have 4 left. If you like I could send a pic of them and see what size and pitch they are. I bought them just long enough that I would have access to safety wire them. Three saws so far and zero chance the muffler will fall off.

It’s no problem if you would like to see a pic and the dimensions.

 

[RED-85-Z51]

Never experienced this on a 290 yet myself.

Sent from my LM-G820 using Tapatalk

 

[Jorswift]

It’s one of a few Stihl models that have this problem. I’ve had a few come through my shop and tried all sorts of loctite and no joy. The muffler falls off within a few minutes.
I went to the dealer and asked him what he does with the Stihls that the muffler falls off of. He told me he uses some sort of epoxy and it could never be removed again but that is the only way to fix it.
That didn’t sound like a glamorous enough repair to me so I found another way.
I ordered socket cap screws that were 105mm long but they only were threaded about 1/4” longer than the factory bolts. They were oversize so I drilled and tapped the cylinder to accept them. Then I ran two nuts up against the part of the bolts where the thread stops. I tightened the nuts and then rounded them off on a grinder so they would fit through the muffler. I also added a washer under the nut. Then I installed the muffler and tightened the two bolts with an Allen wrench. To be certain the muffler would never fall off again I drilled holes in the head of each bolt and safety wired them together.

It’s a lot of work just to keep a muffler on but it was the only way I could think of. I ordered 10 of those bolts and still have 4 left. If you like I could send a pic of them and see what size and pitch they are. I bought them just long enough that I would have access to safety wire them. Three saws so far and zero chance the muffler will fall off.

It’s no problem if you would like to see a pic and the dimensions.

yes if you can please send a pic and dimensions! That would be great! I don’t mind doing the work at all. Tired of it falling off!

 

[Goofaroo]

They were 100mm with 25mm of thread.
6 x 1.00. You’ll need two nuts and two washers also.

Just tighten the nuts up to where the threads stop and round them off to create a shoulder. Drill and tap your cylinder to accept them. Tighten them down and then drill the head for safety wire. Your MS291 muffler will finally stay on. It’s ridiculous that they won’t stay on from the factory. I’m sure by now you’ve noticed what a sloppy fit the original screw is in the cylinder. Seems like very poor quality alloy that the cylinder is cast from.

 

[Goofaroo]

Never experienced this on a 290 yet myself.

Sent from my LM-G820 using Tapatalk

Yep. When people have brought them to me they seemed extremely frustrated. It’s a very strange problem. lol

 

[Goofaroo]

I couldn’t find them on MonsterBolt.com but here are some at Fastenal.

https://www.fastenal.com/products/details/0141717

 

[Goofaroo]

One more thing and I’ll shut up about it.

You need to be sure to tap deep enough after you drill. I didn’t have a bottoming tap so I went as far as I could with a standard tap and then ground the end down to create a bottoming tap to finish them off.

 

[Wood Doctor]

You might try threaded rod rather than bolts and then double nut the ends. That's about the only thing you have not tried. However, that may still not hold the threads going into the cylinder. You are wrestling with a mean gorilla.

 

[Jorswift]

Thank you! I will try the long bolt wired method!

 

[Wood Doctor]

Last year one of my friends tried two lock nuts on the end of threaded rod. He tightened them as much as possible and then welded the two nuts together. It failed. I explained to him that his method was no different that a long bolt. He never understood me.

 

[Goofaroo]

Last year one of my friends tried two lock nuts on the end of threaded rod. He tightened them as much as possible and then welded the two nuts together. It failed. I explained to him that his method was no different that a long bolt. He never understood me.

The only reason for the long bolts is to give you access to safety wire them.

 

[Goofaroo]

Thank you! I will try the long bolt wired method!

How about taking a few pics as you go?
I thought about taking pics and showing them on here as a solution for that problem. Unfortunately I am rarely disciplined enough to take the time to document a repair. However, I really appreciate people on forums that post tutorials with pics. Especially for unusual problems like this.

 

[Jorswift]

How about taking a few pics as you go?
I thought about taking pics and showing them on here as a solution for that problem. Unfortunately I am rarely disciplined enough to take the time to document a repair. However, I really appreciate people on forums that post tutorials with pics. Especially for unusual problems like this.

Yea I probably can do that! I won’t be putting it back together within the next few days though, as I have a few prior engagements! But most definitely can take pics as I go!

 

[Goofaroo]

Yea I probably can do that! I won’t be putting it back together within the next few days though, as I have a few prior engagements! But most definitely can take pics as I go!

Sounds good. All of this has me wondering why there isn’t a Tutorials sticky in the chainsaw section.
I would also like to have a section for build projects and restorations.

Maybe a moderator could chime in? Does anyone else have any interest?

 

[Jorswift]

What about tuning it? How do I access the carb screw to adjust it?

 

[Jorswift]

So I already had the head tapped. I just got the longer bolt, added 2 nuts on it and welded them on together. Rounded them to fit into the muffler ports. I then drilled into the bolt heads for safety wire. Then I cut out a spacer bracket so the bolts won’t be pulling together when wired. Then just wired the bolts in. Hope it holds now!

 

[Goofaroo]

Nice job. If it still falls off the next step would be to bury that saw six feet deep.

 

[Jorswift]

Lol, exactly!