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Stihl Muffler screws

Started by BARPINCHER, July 12, 2013, 01:12:56 PM

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BARPINCHER

Got a Stihl MS 200 rear handle.  HAving trouble keeping muffler bolts tight that bolt it to the jug.  Saw shop has tried new bolts, new bolts with lock washers, new bolts with lock washers and hi temp lock tite.  Nothing seems to work.  Sometimes it will run 1/2 hour and they come loose.  The last time it lasted about 6 hours run time.  Helper somehow did not notice the change in exhaust note and the mis routed exhaust gas melted 2 holes in my brand new brake cover SO........... after I had my own personal meltdown....  1 idea I had was to get longer bolts that end up with the heads exposed instead of recessed, cut spacers to make up the difference, TIG weld the spacer to the muffler then safety wire the new bolt heads together.  Easier or simpler would be great.  I run this saw alot for TSI work and crane removals so I'd like to get it back in service ASAP and permanently--well as permanently as a saw can be!
Serving hunters and the hunted with science based; non-traditional resouce management methods

Al_Smith

I've never seen area handled 200 but assume it uses the same muffler as a 200T .It should have a type of lockwasher which is a serrated type of belleville washer.

It should have M5 .8 by 20 cap screws which I think are around 12 NM torque .I could be wrong best to check the torque specs to make certain .

Now if you have the holes wallered out you might have to tap them out for 6mm .Danged aluminum muffler expands and contracts so much it's had to keep them from rattling loose .The get loose on just about every 200T I've ever wrenched on which by now is quite a few .

BARPINCHER

Thanks,

Your right on with size, specs, washers, and torque.  Done all that multiple times.  Also suspect you are very right about the alum muffler and ya it is the same it appears as the one on my 200T.  I also had a suggestion that I heli coil the jug since the threads have been torqued so many times now.
Serving hunters and the hunted with science based; non-traditional resouce management methods

NCFarmboy

I would drill and tap to M6 as Al suggested.  Then safety wire.  Or change screws to reg hex head and make a safety plate to go under both (now bolts) bolts and bend the corners up to lock the bolt.  Husky used this method on several saws w/ lg. mufflers like models 65-77-2100 to name a few.
Shep
Lots & Lots of Saws

pineywoods

I'll probably get some argument from this, but here goes. Those screws come loose because they were over tightened. The aluminum expands faster and more than the steel screw, which will stretch the screw. When it cools off the aluminum shrinks back, but the screw may not, depending on how much it was stretched. Once a steel screw is stretched beyond a certain limit, it's ruined, throw them away and use new screws. Do NOT OVER TIGHTEN. Going to bigger, harder screws won't fix the problem, just strip out the threads. Classic  example of this is alloy wheels with steel lug bolts on a vehicle. Tighter is not always better.
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BARPINCHER

NC.  I would have already done that lock plate suggestion if it was possible.  Bolts are recessed about 1.5 inches and no room to spare.  I was thinking of doing that but making spacers and longer bolts to get them where I can reach them and get a lock plate underr the bolt heads or safety wire them.

Piney... no arguement except those brand new bolts were torqued as were the 2nd set and the 3rd set.  Concerned tho that  a) running the bolts in and out multiple times b)  there were 3 or so prior attempts to fix that did not involve new bolts + see a) above and c)  I'm not the first owner of this saw and lets just say it's prior mechanic didn't go overboard with making quality repairs.  That is why I'm kind of leaning towards a Heli coil in both holes so I have decent threads to torque the next new set of bolts to...
Still welcome any and all ideas.....

Thanks!
Serving hunters and the hunted with science based; non-traditional resouce management methods

clww

I'd drill the new bolts and safety wire them in place. No need for another piece on top of that, if the SW is performed correctly.
Many Stihl Saws-16"-60"
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Al_Smith

I thought this problem over and arrived at a theory based on several things.

Firstly to get full strength from a threaded fastener tapped into aluminum the thread depth has to be four times the major diameter of the fastener which would be 20 MM .The length of the muffler screws is only 20 so it is designed to rely on the Belleville washer .

It might be such a thing before retapping the holes to try a slightly longer screw using stacked Bellevilles to allow more expansion .

Here's the hot info on Bellevilles http://en.wikipedia.org/wiki/Belleville_washer

 

Al_Smith

Getting back to this thing just a tip for what it's worth .Now yes you can heli-coil a damaged thread hole to a certain extent .It takes a larger hole to install and a special tool and all that .

Now then a stripped out 5 mm hole is just about the correct size for a 6mm by 1 .So it's just a simple matter of first running a 6MM spiral point tap in the hole followed by a 6MM bottoming tap .

Rule of thump for tap hole size is bolt size minus thread spacing .Metric is given in thread spacing ,SAE is given in threads per inch which must be converted to thread spacing .--junk yard dawg tips 101 ---

BARPINCHER

Thanks all!  Good info in all replies.  I'll let you know how I make out once it's done and gets some work hours on the repair.
Serving hunters and the hunted with science based; non-traditional resouce management methods

Stephen1

sawguy had a repair for problem, different size saw, I will look it up tonight.
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