Thread Lock or ?? For Exhaust Mounting Screws

[aesmith]

Hi, This is my chainsaw, a Stihl MS260. The screws for the exhaust keep working loose, a few days ago the two outer screws (26, 28) came loose while I was working. Then yesterday one of the inner screws (25, 27) came right out and was rattling round inside.

I guess that thread lock fluid wouldn't be any good since it gets hot, is that right?

Any other suggestions? I was thinking if I change then to hex head maybe I could make a fold over tab washer for the inside screws.

 

[hotponyshoes]

What size are the screws?
I've got some locking washers that might sort that.. schoor or something..

 

[Agroshield]

Is there a torque spec for them in the manual? Are you tightening to that number?

Drilling the heads and lock wiring could be another option (wire tension needs to pull in the tightening direction).

 

[aesmith]

Thanks. They're M5, originally torx cheese head. Fiddly to drill but I might have a go. I don't know if I could get locking wire in place on the inner screws without it crossing the exhaust port, but maybe that doesn't matter.

I'm going to try spring washers initially, I think I have some slightly longer screws so there's the same length screwed in.

 

[Porkypine]

Shame they aren't studs you could double ( lock) nut them

 

[tom2207]

is there room to use longer screws and put a nut on the back

 

[Agroshield]

I'm going to try spring washers...

Please see:

Helical Spring Washers

Similar (but better) for serrated lock washers:

How Effective Is Serrated Lock Washer?

Serrated washer is a friction-based washer. It might be easy to install, but how secure is the locking ability? Will it damage the mating surface of the application? Experiencing bolt loosening? Assess and compare 11 common bolt locking solutions including serrated washers. Download ebook with...

www.nord-lock.com

Loctite 266 copes with higher temperatures.

 

[indykid]

Because they're holding sheet parts, the screws have barely any stretch. Longer screws with spacer tubes under the heads would give a much more robust joint. You could certainly manage it on the external ones but not sure about the internals of the silencer.

 

[bricol]

Spring washers do stuff all other than act as flat washers with a split in.

Nordlock washers are the bee knees., but expensive.

Stihl being a big name, I can't imagine they'd still be using an inferior method to hand on to things - are they original screws? Room to replace with socket cap heads?

 

[Moose McAlpine]

Stihl typically use conical lock (Belleville type) washers on their exhaust screws.

 

[Kram]

Ah it thinks its a Husqvarna!

Its a problem that should be fixed immediately with no more use until then, or it will end up loosing the bolts and stripping threads. It happened to my G372XP but unfortunately was my only saw big enough to finish the job, I had to continue the job chogging up a 1m dia lime.

While your in there it may be worth checking the alu threads in the head, in case they have started to wallow out. If they have, it would need to be drilled and helicoiled.

With my 372XP repaired (treated her to a new cyl kit with the old as a spare), I simply done the exhaust up a bit tighter and it has been fine since, done quite a bit of work since then.

 

[aesmith]

The inner screws are original, the outer are what I had to hand which were button head Allen. There's room for hex or full size Allen head.

The original screws don't "appear" to be anything special ..

Spline Screw M5 x 16 for Stihl TS400 Disc Cutter - OEM No. 9022 341 0980

Overview: The Spline Screw M5 x 16 for Stihl TS400 Disc Cutter is a Genuine Stihl fastener designed for reliable assembly of key components under vibration and heavy use. Made from durable steel with a corrosion-resistant plated finish, it uses an internal spline drive for positive bit...

www.lsengineers.co.uk

 

[hotponyshoes]

I haven't got any nordlock as small as m5 but I have got some Schnorr, they are 0.5mm thick so should be ok with the original bolts

 

[frank horton]

stud and double nut for the inside, Brass of course.....drill n wire the outers or change em for custom brass bolts with thicker heads if u have a lathe...

 

[aesmith]

I think lock wire might be the answer, but will need to get screws with big enough heads to drill. Does a 1mm hole sound about right?

 

[8ob]

They normally do this when the threads in the barrel are shot, I drill them out as deep as possible and fit long helicoils into them , once done use the longest torx screws you can before they bottom out.

Bob

 

[Agroshield]

Does a 1mm hole sound about right?

Not for 1.2mm wire. Probably too big for 0.5mm wire. Likely OK for 0.7mm wire.

https://www.amazon.co.uk/AB-Tools-US-Pro-Stainless-Lockwire/dp/B07XB1SJ6M

The instructions on the locking wire (or a motorsports or aircraft site) would tell you the correct hole size to drill for a specific diameter of wire.

 

[aesmith]

The wire I have is 0.8mm specifically sold for locking nuts/bolts and 0.9mm "Monel" for rigging screws, shackle etc (boat). I bought the motorsport stuff as it was cheaper and I'd mislaid the boat stuff.