exhaust tags & springs

[johnm]

Help .....................

 

Anyone replaced the tags that the exhaust springs grap on (8 springs - 16 tags)

 

I'll find out from Rotax the optimum stretch 0f the spring and therefore distance between tags ?

 

I reckon the tags on my Rotax were installed to far apart and the springs have cut a fair portion of the tag - I'd say up to 40 % of tag is cut

 

I'm thinking - remove the whole exhaust - assemble it - mark desired location of tag - weld new tags and put it all back - what traps lie waiting when you do this ?

 

If you have done this - your advice would be appreciated

 

Thanks

 

JM

 

 

[tecnamman]

Hi Johnm...in response to your question about replacing the tags...no I haven't replaced them yet, but I noticed at the last oil change and general engine inspection that the apex of the spring eyes had worn very thin on a few of the springs, and I'm certain I would have lost a couple by the next oil change from fatigue.

 

I changed all the springs as a precaution with new ones and applied high temp nickel anti seize to the tags/springs...too early to tell yet if this will reduce the wear factor (only done about 10 hours since applying) but works in other engineering applications so reasonably confident. I have also filled the spring centres with high temp silicone rubber to reduce harmonics...this is recommended by Rotax but not widely known.

 

My engine has 130 airswitch hours , and like you I was very surprised/alarmed to find the tags had worn so much in so few hours. I haven't measured the tags with a vernier, but the Mk 1 eyeball estimator says 25 %. A few of the springs had worn down to 50% of original diameter, some a bit less. How many hours has your engine clocked?

 

Like you, I would like to hear from any LAME's or Level 2 guys who have had to replace the tags.

 

I remember ringing Bert Flood and asking about this problem ....they gave me the Rotax recommended spacing between the tags but can't recall at present....suggest giving them a call, I've always found them very helpful and happy to give advise over the phone.

 

Hopefully some Rotax gurus out might like to add their 2 bobs worth so we can both find out!

 

Cheers Johnm

 

 

[johnm]

tecnamman

 

Next time ? you add to the thread please advise the 'maker' for the nickle product - sounds like a good idea

 

This Rotax done 340 hours - air switch

 

Interesting to hear that you say 'the spring eye is worn' - I'm sure mine was only the tag - I'll recheck

 

Interesting to hear that I'm not the only one with this issue - I'm wondering if the grade of steel used in the tag could be something to consider

 

The rest of you 'sprung held together exhaust pilots' might also want to check

 

JM

 

 

[Guest Cloudsuck]

In my first few of hours I kept breaking springs. They would break at the apex of the hook. I was loosing one per flight. I rang Rotax and as usual they said that it was a Tecnam fault and that tags sould not be any more than 66mm apart and that the springs were over streached. I went back and measured the tags and they were less than 66mm so that wasn't the problem.

 

I then replaced the springs with some other brand that I had lying around and have not broken one since. I also put on extra springs where I could. I think that the Rotax springs are too hard and brittle.

 

I have noticed some wear on the tags but don't know if this was from the the old hard springs or not. On my daily inspection, I always check that all the springs are there.

 

 

[tecnamman]

Johnm

 

Hopefully.. photos of an exhaust spring attached showing the extent of erosion after approx 100 hours. I couldn't find one of the badly worn ones to show you.... this one is about half through.

 

The anti seize is Loctite 771 but also available in Permatex etc..available from bolt bars, bearing shops etc. Use sparingly as you don't want excess falling on the muffler.

 

If I was flying a 'pusher', I'd be checkin the springs with a microscope before flight..a spring into the prop..ouch!!

 

Since I filled the springs with silicone I haven't broken another one but note they are still wearing...but like cloudsuck a couple of springs went 'missing' in the first couple of months until I remembered that we used to do this to the exhaust springs on our MX bikes, as they tended to suffer the same fate.

 

I don't believe applying beads on the outside of the spring is as effective.

 

Cheers

 

 

 

 

[facthunter]

Wear on springs/tabs.

 

Like you say ...not a good idea on a pusher. I would be inclined to think that harmonics are the cause of the wear and the tension has a bearing on just where these occurr, but it's beyond our capabilities to assess these in the field. I would try to damp them with the black silicon and put a strong stainless wire through the spring and the hole in the tabs to catch the spring if it detaches, and inspect pretty often.... NEV.

 

 

[Guest ozzie]

this is an old problem and i am surprised to hear that people are still being caught out. after fitting the springs to rotaxes recommendations, run some silastic or stag along the length of the spring to stop the zing from wearing out the ends, add antisieze were the spring rubs the tag and LOCKWIRE the damm things on so if they do break the obvious won't happen. inspect them on every DAILY preflight inspection.

 

 

[tecnamman]

Ossie

 

Hopefully, hopefully, one day, in my liftime, the RAA will be in a position to conduct regional workshops run by experienced engine mechanics/reconditioners to teach owner maintainers how to look after their engines and the pitfalls to look for.

 

I agree with you that newcomers shouldn't have to keep reinventing the wheel, and most LAMEs and level 2's who work on RAA should inform their customers the things to keep an eye on.

 

I have a background in automotive maintenance and would desperately like to learn more about aircraft maintenance but where do you start???...no courses to study unless you know a LAME or level 2 who is willing to teach you.

 

Perhaps Floods...seeing as how they are the Aus agents for Rotax....???

 

Anyway, this is way off the topic but something that urgently needs addressing and a good subject for another thread....??

 

Cheeers

 

 

[Yenn]

I had this problem years ago with an old 503 Rotax. I welded washers to the tags to reinforce the worn edge of the hole.

 

 

[johnm]

Come on guys, concentrate (some are)

 

91.5979993 % know about mastic on / in / near / around the exhaust spring and subsequent lack of spring breakage

 

The issue is wear of the spring and tag - until one day ther is nothing left to hang your spring from

 

Or is the answer big mobs of mastic - no harmonics - no wear - is that what you exhaust spring pilots are trying to say ?

 

JM

 

 

[Guest ozzie]

Rotax courses

 

This would be as close as you could get to doing a course in OZ.

 

With our smallish market preventive maintnence and home rebuilds would not be of a benifit to those who make their income from this work so they possibly would not promote courses. they would prefer things to break.

 

 

 

[Guest Cloudsuck]

Come on guys, concentrate (some are)91.5979993 % know about mastic on / in / near / around the exhaust spring and subsequent lack of spring breakage

 

The issue is wear of the spring and tag - until one day ther is nothing left to hang your spring from

 

Or is the answer big mobs of mastic - no harmonics - no wear - is that what you exhaust spring pilots are trying to say ?

 

JM

Every one of my broken springs had 'mastic' (red silicone on them). My new springs don't and have never broken. They break at the hook, the silicone made no difference. The answer is poor quality Rotax springs.

 

 

[Guest ozzie]

Any sharp edges on the tag, i assume you are not using a piece of flat metal with a hole in it to hook the spring onto. it should be a piece of rod the same dia and material type as the spring bent to a half circle and welded on. There are also limits on the stretched length from memory and the use of regularly applied antisieze where the spring and tag rub. how are your engine and muffler mount rubbers? no excessive movement.

 

 

[Guest Maj Millard]

Did 600 hrs on a 582, never broke one spring, with hi- temp silastic on them. Thought I would get fancy, and put on a whole new set of rotax springs, was then breaking one, and sometimes two springs every flying hour !!....what the.?.....they also had red hitemp on them. Wal pretty much admitted that Rotax did have a bad batch of springs go through the system. Hopefully now they are out of the system !!. Also what Oz says above is appropiate.

 

 

[johnm]

merry xmas tecnam owners. hope I am not dwelling on it but ..............

 

this is the tag that was 'cut' by an exhaust spring - probably about 65% of tag remained and 35% had gone - a spot of stainless steel weld and gound flush - costed $ 10 so its back to the salt mines for another 2 weeks - installed 'Locktite 717' as recommended (don't forget the bloody red mastic)

 

the intent of starting this post was for you 'exhaust spring pilots' to check this wear - have a look if you have not looked yet

 

interestingly it only occured on one tag (pilot side front piston - tag closest prop) - all the others OK. Even the tag at the opposite end of the spring was OK. Trusting Locktite 717 is the answer (oh and I have n't forgetten the bloody red mastic)