stihl 440 muffler bolts

[OneWithWood]

The two long screws that hold the muffler housing at the bottom on my Stihl 440 fall out because the holes have become stripped and/or hollowed out.
Is there a fix I can employ rather than replacing the casing?
I tried Loctite but the threads are too far gone.  Screws fell out first time I used it.

[sawguy21]

Is there enough surrounding material to allow the use of a Helicoil insert?

[bedway]

I know of many people with the same problem. Its not just one brand of saw. This is a design flaw but the manufactures will never make it right. Sorry I don't have a fix but your not in this alone.

[Ada Shaker]

I would have imagined that silver soldering a couple of studs into the hole (just wondering if it can be done), and then using a couple of brass nuts to mount the exhaust. I say brass nuts because I've had good results using brass nuts on vehicle exhaust studs, never had one snap off whilst using brass nuts, learned that from an old timer in my younger days when he advised that the old FJ Holdens used brass nuts on the exhaust and they never snaped a stud.  So now this little bit of info is really old school, and am contemplating using brass screws/bolts/nuts on the exhaust of all my saws, seeing they're  an issue.

[Stihlowner]

I would try HeliCoil or Time-Sert. Both of these methods would make a good repair.
Just did the exhaust manifold bolt holes on a 2 cycle engine with HeliCoiL.
Strong repair.
Both methods will set you back a few dollars.
You might be able to just drill and tap a larger hole too.
The HeliCoil and Time-Sert also require a larger hole to be drilled but when the job is finished you will still be using the original size bolts.

[Ada Shaker]

I would try HeliCoil or Time-Sert. Both of these methods would make a good repair.
Just did the exhaust manifold bolt holes on a 2 cycle engine with HeliCoiL.
Strong repair.
Both methods will set you back a few dollars.
You might be able to just drill and tap a larger hole too.
The HeliCoil and Time-Sert also require a larger hole to be drilled but when the job is finished you will still be using the original size bolts.

My personal experience with helicoils has not been that great. They're ok if you don't intend on ever removing the screw again, but I wouldn't use it on an item I would be servicing, as they do have a tendancy of unwinding themselves and making a mess when screws/bolts are removed. A new one then has to be refitted. I would imagine that a threaded insert such as the timesert would work better, there are press fitted ones also that only require drilling, no tapping. If you decide to go down the path of helicoils, I would go the standard (non locked) ones. They both require the use of three taps to get the job done. Might as well just drill'n'tap to the next size up if you can which also requires the use of three taps. But I recon the key is to use brass screws/bolts...etc. on the exhaust.

[sablatnic]

I prefer Time Sert from Würth.

wurthusa.com/web/en/website/produkte_1/service___repair/thread_repair/time_sert.php

[Stihlowner]

I would try HeliCoil or Time-Sert. Both of these methods would make a good repair.
Just did the exhaust manifold bolt holes on a 2 cycle engine with HeliCoiL.
Strong repair.
Both methods will set you back a few dollars.
You might be able to just drill and tap a larger hole too.
The HeliCoil and Time-Sert also require a larger hole to be drilled but when the job is finished you will still be using the original size bolts.

My personal experience with helicoils has not been that great. They're ok if you don't intend on ever removing the screw again, but I wouldn't use it on an item I would be servicing, as they do have a tendancy of unwinding themselves and making a mess when screws/bolts are removed. A new one then has to be refitted. I would imagine that a threaded insert such as the timesert would work better, there are press fitted ones also that only require drilling, no tapping. If you decide to go down the path of helicoils, I would go the standard (non locked) ones. They both require the use of three taps to get the job done. Might as well just drill'n'tap to the next size up if you can which also requires the use of three taps. But I recon the key is to use brass screws/bolts...etc. on the exhaust.

All right Ada, teach me something new today.
Why three taps?
Got me thinking but I can't come up with anything.
Always interested in learning a new trick.
Even if I am an old dog.

Look, I even got the post right using the quote function.
Moderator should be happy I'm learning like he suggested.

[Texas-Jim]

I have on occasion drilled and re tapped the hole. Then screw in a grade two bolt and lock tite it. i then cut the bolt off even with the block and drill and tap the bolt. Kinda a poor mans heli coil but uses very little space and its cheap.

[ohiowoodchuck]

Time serts all the way. I have used them to repair glow plugs threads in diesels after heli coils kept blowing out.

[Ada Shaker]

I would try HeliCoil or Time-Sert. Both of these methods would make a good repair.
Just did the exhaust manifold bolt holes on a 2 cycle engine with HeliCoiL.
Strong repair.
Both methods will set you back a few dollars.
You might be able to just drill and tap a larger hole too.
The HeliCoil and Time-Sert also require a larger hole to be drilled but when the job is finished you will still be using the original size bolts.

My personal experience with helicoils has not been that great. They're ok if you don't intend on ever removing the screw again, but I wouldn't use it on an item I would be servicing, as they do have a tendancy of unwinding themselves and making a mess when screws/bolts are removed. A new one then has to be refitted. I would imagine that a threaded insert such as the timesert would work better, there are press fitted ones also that only require drilling, no tapping. If you decide to go down the path of helicoils, I would go the standard (non locked) ones. They both require the use of three taps to get the job done. Might as well just drill'n'tap to the next size up if you can which also requires the use of three taps. But I recon the key is to use brass screws/bolts...etc. on the exhaust.

All right Ada, teach me something new today.
Why three taps?
Got me thinking but I can't come up with anything.
Always interested in learning a new trick.
Even if I am an old dog.

Look, I even got the post right using the quote function.
Moderator should be happy I'm learning like he suggested.

For anyone wanting technical info on helicoils should refer to the product technical/engineering manual.

http://www.noblefix.com/PDF/Helicoil/HeliCoil-Catalogue.pdf

No need to teach and old dog new tricks, but for those wanting to tap bored holes they are through, intermediate,  & bottoming taps. Through holes only require through taps as the whole tap clears the hole. Bored holes require the use of three taps starting with the through tap to commence the thread and finishing with the bottoming tap. Synthetic oil is not recommended :D but the use of a cutting compound is, there is no mixing ratio ok :D. The taps provided with helicoils are specialty taps of the specific diameter and pitch to suit the thread they're ment to replace. Overboaring can cause weaknesses in the parent material. Incompatible materials (parent stock Vs helicoil) may also cause galvanic action, (which may be why they recommend a protective layer).

[joe_indi]

The 440 has M6X20 screws at the bottom. If I guessed right those holes can accept longer screws like the M6Xx30 screws that are used on a 460.
There will be some thread beyond the 20mm point
Try  a M6X30 in one of those holes and see if it can be screwed right down to its head. I think it will work.
If a bit of the head sticks out, either trim the length of the M6 screw or use some washers. This might be the easiest fix.
Joe

[pineywoods]

Ever wonder WHY them bolts come loose ? Not as simple as it looks...They don't  just un-screw. Bolts (screws) will stretch when the hot muffler expands. Re-tighteng just makes the problem worse. Eventually the screw will reach it's stretch limit and the the threads in the head will strip. Prevention...Use NEW screws and DO NOT OVER TIGHTEN.. there is a torque spec for those screws that looks too loose. NOT... believe the torque specs...

[joe_indi]

Ever wonder WHY them bolts come loose ?

Stihl screws have teeth under the screwheads for staying locked in position, they are also called self-locking screws. But, after a couple of times of removal and tightening the teeth lose their bite, after which they tend to become loose. It would be a good idea to replace these screws after the 4th or 5th removal.