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Exhaust coming loose on OS


Nigel R
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Frustrating to say the least. I have an os with a silencer, the old style, that insists on coming loose every flight. I'm sure at this point the aluminium thread on the can is probably fretted away too much to rescue and the thing will never stay tight.

 

I'm about in the point of ordering one of the just engines replacements. 

 

Open to any suggestions on keeping the cans done up, anyone suffered the same issue and cured it?

 

Epoxy in the thread?

Thread locker?

 

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Hi Nigel don't use a gasket etc . Apply a thin bead of epoxy around  the edge of the mounting flange. I use the standard 24 hour epoxy for this. Make sure the screws threads are oiled and just them screw up. It will make an oil tight joint and secure the exhaust. When you want to remove it simply unscrew the two fixing screws and give the dilence a sharp tap. 

Also make sure that the prop is balanced as vibes fro unbalanced prop can shake  exhausts loose besides causing other failures on engine and airframe. 

Edited by Engine Doctor
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Hi Nigel  ignore my previous post it was for a two stroke muffler. Had visitor and run out of time to edit post . If thread is damaged or worn in a four stroke head then it's very difficult to get a tight fitting  that will remain done up. Also almost impossible to repair as very little material around the head fitting. Epoxy won't work as the fs exhaust gets too hot. Try fitting a bracket to the can that then fits to an engine bearing bolt . This will support the can and take some strain off of the exhaust fitting in the head. Only other remedy will  be to find a head with a good thread .

Edited by Engine Doctor
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Thanks ED

 

Fortunately the thing coming loose is the can itself - not the threaded coupler at the motor end. That end of things has always been solid.

 

Bracket for support sounds good, but would that still aply?

 

When first fitted, I had a flexi pipe joining the standard coupler to the can, and the can was mounted on a bracket. The can came loose whilst on this arrangement (right before the flexi pipe cracked) Perhaps the thread has always been a bit loose or worn?

 

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OK if its just the can try the following . Tighten fully and run up to full temp and stop engine. While still hot snug up the lock nut again. Using two spanners , one on nut other on can. It's always worked for me. 

Of course if thread is very loose it may be time yo find a new can. When loose they wear very quickly when engine is running as shown  by a lot of grey oil residue.

E.D.

Edited by Engine Doctor
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I have found what ED suggests above to work well  if tve thread in the cab is a little worn you could try wrapping some PTFE pipe tape round the manifold pipe before you screw the can on. Then follow the  steps as outlined by ED above. Has worked in the past for me 

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Hmm. Sadly it's been snugged when hot - first thing I tried. I haven't tried PTFE tape yet... I do have a roll of the stuff. Will try that before splashing out on a new can.

 

The can itself was second hand, it came from a 91 that also boasted a warped crankcase and bent rod (advert read along lines of "runs great, excellent condition", hmm, I think not).

 

 

Just noticed I made an error earlier in the thread,

 

Quote

81 four stroke, using a baffled can from JuSt engines. 

 

actually should say I'm using a baffled can from OS 91, I'm thinking of buying a baffled can from JE, obviously one of my friday afternoon quality posts there

Edited by Nigel R
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22 hours ago, Nick Somerville said:

If you decide to change the muffler and want to reduce noise I highly recommend the Weston four stroke quiet pipes. I have one for my Wot4 XL OS 120 pumped combo and it is has a superb soft note that is often commented on.

 

That's interesting. I was thinking of adding one to the OS 52 in my Baron and flying it in La Coupe Des Barons next month, after all I've a title to defend now! ?

 

Whispering Death indeed!

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In my case the pressure nipple has been blocked off as the engine is the pumped version. As I bought the model and engine together 2nd hand I had assumed the pipe and header had come together but now thinking about it, probably a separate  purchase by the original owner.
 

BTW the engine is the Surpass MK2 pumped 120 and is one of the nicest engines I have ever owned. It needed new bearings when I first got it (thanks Jon) but since has run flawlessly. In particular it has such a responsive and smooth throttle curve. 

 

image.thumb.jpeg.31f1cfdf4ffc3de6afce0369bbccfeb9.jpeg

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nice one Nick - many thanks

 

explains why I couldn't see the thread!

 

are they particularly heavy units?

 

now very interested, if I'm going to spring for a new can, it might as well be one that does the biz, as it were

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