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Exhaust thread worn out

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Glenn Stevenson19/06/2018 22:27:33
11 forum posts

Hi, my exhaust fell out of my OS70 fs this aftrenoon, into the long grass of course!

It had come loose earlier and I refitted it tightly. Looks like the threads in the head are worn. Do I have to buy a new head (plus exhaust and silencer) or can the thread be repaired?

Regards

Glenn

Glenn Stevenson19/06/2018 22:30:11
11 forum posts

Before anyone corrects me I realise that I mistyped afternoon.

CARPERFECT19/06/2018 22:40:52
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354 forum posts
5 photos
Stripped Glow Plug Threads?
£16.00 Contact this man on the BMFA CLASSIFIED. He does exhaust threads as well. You will find him under Services
David Ovenden20/06/2018 05:15:40
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317 forum posts
15 photos

Have you tried wrapping the exhaust pipe thread with PTFE tape before you screw it into the head and tighten the nut? Might be enough to keep you flying for a while.

Glenn Stevenson20/06/2018 07:11:16
11 forum posts

I would wrap it in anything that could work if I can find it.

The long grass keeps everything it catches including my friends 30cc petrol engine that jumped out of his plane!

Tom Sharp 220/06/2018 07:16:25
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2953 forum posts
16 photos

30 cc petrol engine lost, I hope your friend informed the farmer. cool

Denis Watkins20/06/2018 07:22:16
2812 forum posts
141 photos

Just engines have your header pipe, lock nuts and silencer in stock Glenn,

Glenn Stevenson20/06/2018 08:37:21
11 forum posts

No point buying the exhaust without mending the head

Engine Doctor20/06/2018 08:43:32
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1968 forum posts
19 photos

If the head thread is worn ,usually due to exhaust loosening , then you will have to buy a new head I may be wrong but I don't think anyone repairs them as there isn't enough metal to tap into to insert a heli-coil or similar.

You may find an model engineer who can cut a new stub thread a bit oversize that will screw into the existing thread or whats left of it .

Best bet is to try and source a good secondhand cyl head but may be difficult. There must be thousands lying around in workshops but modelers seem reluctant to break or sell old four-strokes ?.

When you get it sorted the best way I have found to tighten the exhaust into the head is as follows .

First and very important is balance the prop . Its the vibes that shake the unsupported exhaust loose..If engine still vibrates badly then sort the problem as exhaust will keep loosening on a badly vibrating engine .

Screw the exhaust into the head until it wont go any further then back of to adjust angle and tighten lock-nut using a good fitting spanner. Run engine up to temp and stop it ,then quickly re tighten the lock nut firmly while engine is still hot.

Hope you manage to source a new head .

Biggles' Elder Brother - Moderator20/06/2018 09:46:59
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Moderator
15349 forum posts
1409 photos

"Exhaust thread worn out", I wish the Electric Car thread was,.....sad

BEB

Denis Watkins20/06/2018 10:26:38
2812 forum posts
141 photos
Posted by Glenn Stevenson on 19/06/2018 22:27:33:

Hi, my exhaust fell out of my OS70 fs this aftrenoon, into the long grass of course!

It had come loose earlier and I refitted it tightly. Looks like the threads in the head are worn. Do I have to buy a new head (plus exhaust and silencer) or can the thread be repaired?

Regards

Glenn

Have just looked at my 70, fearing the worst could happen to me, resulting in minimum £100 parts and repair, and 2 things stop mine falling off completely.

1. The pressure pipe attached to the silencer is a tight fit, and

2. If the header pipe became loose, the silencer falls and hits the model, preventing full detachment.

So you were unlucky Glen.

Alerted by your plight, have put a cotton thread around the pressure nipple, and wound this along the breather pipe to the model via screw.

Am also rebalancing the props on my 4 strokes,

Also on two models have drilled a pilot hole to insert a cocktail stick in the arc of any future movement of headers

So they cannot leave the model in the air

kc20/06/2018 10:28:53
5487 forum posts
161 photos

Call in the local metal detecting enthusiast to find the silencer & engine? ( do they detect aluminium etc?)

Glenn Stevenson20/06/2018 11:20:15
11 forum posts

My silencer prevented rotation by stopping against the fuselage, so I am guessing that the threads were worn enough to allow the pipe to wobble out. It screwed in and tightened up in a way that felt like it was secure enough.

Hope my 52 and 91 dont go the same way.

Engine Doctor20/06/2018 12:41:19
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1968 forum posts
19 photos
Posted by Biggles' Elder Brother - Moderator on 20/06/2018 09:46:59:

"Exhaust thread worn out", I wish the Electric Car thread was,.....sad

BEB

yes and the football and tennis were finished !

John Stainforth20/06/2018 20:03:23
194 forum posts
38 photos

Clarence Lee Custom Engines in California repairs threads in cylinder heads - if he is still in business.

Peter Robinson 921/06/2018 08:36:00
1 forum posts

Hi

i had a similar problem with my NGH38 with vibration. The fix I found was to retap the threads from 4mm to 5mm using a plug tap. The view I took was its damaged any way so nothing to lose. This meant ordering some 5mm cap head bolts and chopping the heads off and using them as studs, then use stud lock to lock them in place and use nuts to tighten the silencer etc. Just a suggestion.

Peter

Engine Doctor25/06/2018 14:11:00
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1968 forum posts
19 photos
Posted by Peter Robinson 9 on 21/06/2018 08:36:00:

Hi

This meant ordering some 5mm cap head bolts and chopping the heads off and using them as studs, then use stud lock to lock them in place and use nuts to tighten the silencer etc. Just a suggestion.

Peter

It won't work on he smaller rs engines as they have a totally different mounting system . Good idea but not for the OS 70 and similar.

E.D.

bert baker25/06/2018 16:15:05
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1155 forum posts
249 photos

There was and probably still a chap offering the services you require on the BMFA adds,,I would try him first,,

In production helicoils are sometimes used from new to give a better hold,, plus a helicoil can put up having bolts repeatedly removed better than plain aluminium

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