MS391 Exhaust Screws Come Loose

[Jimbo54]

I got an MS391, had it from new 12 years ago, medium-light use felling and bucking firewood. Its eaten a couple of exhaust cowls over the years, but the last one I fitted seems to not want to stay with the saw. I put the two screws that hold the cowl on, into their threads with thread locker, but it seems every 3-4 hours of run, they come loose and I have to re-tighten them. The cowl has a kinda heatsink plate between it and the cylinder, dunno if that is relevant, don't think there was one when I took the very first cowl off. The threadlock goo just isn't doing it any more, and I've tried several types. I'm thinking of using extended screws so they project beyond the cowl, then I can wire then, but that seems a bit over the top....anyone seen this kind of problem before and managed to fix it?

Thanks

Jim

 

[thompsoncustom]

are you using a thread locker rated for that kind of heat? Red loctite won't with stand heat above 350-450 degrees I believe and your muffler is way above that.

You need something heat rated like rocksett (1200 degrees)

 

[Jimbo54]

I tried three of four different types of locker, all heat rated....and it never happened before, just since this last cowl....

 

[Chevboy0167]

https://www.amazon.com/Vibra-TITE-19960-Temperature-Threadlocker-Translucent/dp/B07XW2ZTZL

 

[Wood Doctor]

Jimbo54 said, "I'm thinking of using extended screws so they project beyond the cowl..."
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Unfortunately finding extended screws like these are scarce as hens' teeth and the OEM screws make double nutting really tough.

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You might want to try an ordinary lock washer or a lock nut to see if that works. It has for me. Tighten it like mad and keep your fingers crossed. Good Luck!

 

[thompsoncustom]

Jimbo54 said, "I'm thinking of using extended screws so they project beyond the cowl..."
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Unfortunately finding extended screws like these are scarce as hens' teeth and the OEM screws make double nutting really tough.

View attachment 1189914\
You might want to try an ordinary lock washer or a lock nut to see if that works. It has for me. Tighten it like mad and keep your fingers crossed. Good Luck!

what about just making your own? If you found a standard bolt the right length it would be simple enough to reshape the head if it has to be square like the picture.

 

[ballisticdoughnut]

Replace the studs and lock nuts with new OEM parts. Technically speaking, any type of locking fastener is one time use.

 

[Jimbo54]

Thanks for all the replies, guys! I have got some studding (threaded rod) and nuts, locked the nuts onto the studding the right length from one end to act like screw heads to hold the cowl on, while the other end of the studding projects out of the hole in the cowl. I put the extended screws in, then wired them so they can't vibrate loose....It took me longer to write this than it did to make the parts....
Having said that, Thanks to ChevBoy for the suggestion of HotLock, but I'm in the UK, and Amazon over here wants £60 for a bottle of that stuff....its cheaper (and it might be said, better engineering practice) to make the extended bolts and wire 'em