Crack in Exhaust of XT 912

[Bluey]

Hi All;

 

After this mornings flight I noticed a rather large crack in the S bend of my XT 912 exhaust (the bit that has the EGT probe stuck in it). I don't know how long it has been there for but I don't think it has been long. I went for another flight (30min) and it didn't seem to get any worse. However a repair will be pretty urgently called for. Has this happened to anyone else. The crack is somewhat running parallel to the shape of the tube for most of its length. See the pictures. I can feel a smaller crack on the opposite side that I cannot see. Pictures aren't the sharpest thanks to the camera phone but they are good enough to see the extent of the damage. I'm thinking of going for another fly tomorrow morning to see if it changes.

 

Pictures are in attachments

 

Bluey

 

 

 

 

[Guest Maj Millard]

Bluey, Looks like a radial stress crack probabily due to the way things are mounted. I had a similiar one in the Lightwing, because my muffler was bumping against the firewall occasionally.

 

You need to find a quality welder who knows what rod to use with 305 stainless. If the right rod is not used, it won't last. The marine industry welds a lot of stainless exhaust systems. Once welded properly you'll not have any more problems. You do need to look for what is putting the pipe under stress though................................................Maj...

 

 

[Mc Guyver]

Hi Bluey,

 

Your best bet is to get a replacement from Airborne.

 

I don't think it would cost you much more than having it welded.

 

Invariably if you have welded the stainless, after a short time you will find another crack very near to the weld

 

 

[Bluey]

Yeah thanks I was thinking of getting a new one instead of going to all the trouble of getting a decent weld done. Flew this morning and after nearly 2 hours it seemed unchanged. Will be ordering a replacement next week probably.

 

Bluey

 

 

[Bluey]

After talking to airborne about it the cost of replacing the short pipe is $570 plus delivery. So I think I will get it repaired probably by them. They also claim that they have never had a steel exhaust crack like this unless there are engine vibrations caused by carbies that are out of sync. This doesn't seem right to me as I am pretty sure the engine is running smoothly. There are no obvious vibrations in flight, during full power, cruise or even at idle. Having said that, I will get a second opinion. The crack seems to be unusual for a vibration induced failure given that it is running parallel to the length of the pipe. Also, airborne bend this particular pipe themselves as bert floods supplies them straight. It is possible that it could have been damaged during the shaping process. Anyine have any comments?

 

Bluey

 

 

[facthunter]

general comment.

 

912's do get exhaust cracks in a lot of applications, as do many other motors. There are always vibrations. How the system is supported is important. Does your system have ball faced joins with springs keeping the surfaces together. If there is are cracks on opposite sides of a bend then it is probably flexing. You could not rule out there being a weakness formed during the original bend process. Stainless does crack more than mild steel but you can get thinner wall thickness so it is lighter. It is tough to work but ductile. A graphite pencil mark left on a pipe will make it crack later . It should weld OK, done properly with the correct rod and technique...Nev

 

 

[Bluey]

Thanks Nev, it is a ball and spring design and there are no other signs of other cracks. The exhaust is mild steel not stainless steel.

 

Bluey

 

 

[cscotthendry]

A graphite pencil mark left on a pipe will make it crack later . Nev

That's amazing! Can you explain why that is?

 

 

[dazza 38]

My 2 cents worth, Graphite- at high temperatures can cause stainless Steel to Caburize.It promotes corrosion, cracks and pinholes etc.Loss of metal as well.

 

 

[facthunter]

Graphite.

 

Yes the carbon infuses into the metal with the heat of operation and makes the alloy brittle. Nev

 

 

[Mc Guyver]

Yes the carbon infuses into the metal with the heat of operation and makes the alloy brittle. Nev

And even worse I believe on aluminium

 

 

[facthunter]

Bach to the Repair.

 

If you can clean the inside of the pipe, a good weld repair should be satisfactory. If the pipe is MS it will be fairly thick and MS has a good fatigue resistance. Nev

 

 

[cscotthendry]

Ah yes. From the little materials science I studied in college that sounds spot on. In fact the steel making process is mostly about removing carbon from iron. Thanks for the enlightenment. It sounded totally crazy at first.

 

 

[Bluey]

I removed the piece of offending pipe this morning and will be sending it up to airborne tomorrow for the repair. The crack on the other side is not as bad. I'll post good quality pics later when I get a chance.

 

Bluey

 

 

[icebob]

Hi bluey,

 

I had the same issue a while back, replaced the pipe and within 250 hours it happened again. Found out the location springs at the ball joint were of different "pull" or "load", causing an amount of vibration at the bend and striking a wire reinforced hose every so often, got new springs(and hose) and tested the pull of the new springs to get close to equal as possible, problem fixed. So if it happens again look at the springs.

 

bob.

 

 

[Guest Andys@coffs]

In fact considering the cost of springs vs the replacement cost of the muffler....why wait

 

Andy

 

 

[Bluey]

[ATTACH]12711.vB[/ATTACH][ATTACH]12712.vB[/ATTACH][ATTACH]12713.vB[/ATTACH][ATTACH]12714.vB[/ATTACH][ATTACH]12715.vB[/ATTACH][ATTACH]12716.vB[/ATTACH]Has anyone had problems with exhaust springs breaking? I pulled off a number of the springs and some are pitted. I am definitely going to replace the lot. Also, after installing the repaired pipe and attaching and safety wiring all of the springs, part of the exhaust came apart during a short test flight. The strange thing is that I didn't detect any real increase in noise. Anyway, after landing I wondered how this could have happened and then noticed that one of the lugs was nearly worn through. So I will have to remove all the suspect bits and have them repaired before flying again. The exhaust coming apart could be indicative of stress in the system. The welder reckons there had to have been lots of stress to cause the damage he saw in the pipe he repaired. The exhaust coming apart could be evidence of this or it could just be that I somehow didn't[ATTACH]12710.vB[/ATTACH] put it together right??? Is there an order that the pipes need to be re-attached in so they are properly loaded and balanced? Check out the photos.

 

[ATTACH]12709.vB[/ATTACH]Bluey

 

 

 

 

 

 

 

 

 

 

 

[Guest Maj Millard]

Bluey, looking at photos 7 & 8 it appears they have been leaking ????.....which would indicate a less than adequet seal on those joints. I use a silver anti-sieze paste on exhaust joints (light film) which assists them in 'bedding in' for a good leakfree seal. Also your exhaust-can needs to be adequetly supported on it's own, and not requiring the exhaust pipes to assist in supporting the muffler can.Two spings in good condition should be sufficient for maintaining a seal, and occasionally you see three springs used..The pipes should align easily with the sockets, if you have to force them over, this is where the stress comes in. It is better to heat them up and align them properly, for an easy no-stress fit........................Maj...

 

 

[icebob]

Hi Bluey,

 

Have to agree with the Maj, incorrect assembly and/or stress. Was there support for the "can"? I have seen a number of motors with only one support for the muffler can, that is not enough need at least two if you can. The lugs are a known issue most of the time it is caused by over stressing due in part to poor alignment or weak springs that wear the hole in one spot.

 

When you have everything re-assembled get someone to start up for you and look at the vibration and movement of your motor that will give you some idea of the actual movement of your motor, also have you checked the engine mounts are not getting soft too?

 

Bob.

 

 

[Bluey]

Engine vibration seems minimal. We started it up and felt the engine in order to sense its movment. Visually it seemed very steady. I have used anti-seaze grease on it but the part that came loose has never been touched. I will make sure to use ant-isieze on all the ball joints when it finally is re-assembled.

 

Bluey

 

 

[facthunter]

Muffler Mounting.

 

Is the way the muffler is mounted standard? It looks as though the weight of the muffler is supported by the exhaust pipes It should be supported in its own right and only supported by attachments to the engine . ( It has to move with the engine). Nev

 

 

[pudestcon]

I use a silver anti-sieze paste on exhaust joints (light film) which assists them in 'bedding in' for a good leakfree seal. Maj...

Maj, Would you care to let me know what the anti-seize paste is please?

 

My T500 582 was fired up on Saturday with 1:40 oil/fuel mix for running in, and I noticed oil leaking from the exhaust joint where the bend coupling attaches to the manifold. Would the anti-seize paste assist here? We did not proceed with the run in procedure.

 

Pud

 

 

[Guest Maj Millard]

Hi There Pud, I believe the stuff I use is a Locktite product. Its in a black tube, any good bearing place should carry it, or something similiar. Often it is referred to as 'nickle anti-sieze'.

 

It is not meant as a sealant, so I don't know if it will stop the oil leakage in your case, as it may take an hour or two to settle things in a bit.

 

Generally we use it in the industry as a barrier againt corrosion between aluminum and steel, as in the case on sparkplugs.

 

Good to hear you are making noise over there at last Pud.................Maj...

 

 

[pudestcon]

Hi There Pud, I believe the stuff I use is a Locktite product. Its in a black tube, any good bearing place should carry it, or something similiar. Often it is referred to as 'nickle anti-sieze'.It is not meant as a sealant, so I don't know if it will stop the oil leakage in your case, as it may take an hour or two to settle things in a bit.

Generally we use it in the industry as a barrier againt corrosion between aluminum and steel, as in the case on sparkplugs.

 

Good to hear you are making noise over there at last Pud.................Maj...

Thanks Maj,

 

Yes it was music to the ears:laugh: It sounds really good with excellent response and no abnormal vibration that I could see. The run in process will be completed once the aircraft is secured properly so it can't move at full revs.

 

We still have a few things to go before test flying - Wayne Fisher is doing the wing skins for me and some decisions need to be made regarding the undercarriage springs. The wheels are 'splayed' out already with no wings, fuel or pilot yet. I want to acquire a template or drawings/specifications of the correct spring configuration so I can check it out.

 

Cheers,

 

Pud

 

 

[icebob]

[ATTACH=CONFIG]19892[/ATTACH]

 

The photo is only one of a number I took that addresses the problem, am unable to insert the rest, maybe poor quality photos?

 

You can see where the crack on the bend was welded up and then the bracket added.

 

Bob.