Microlighters

Posted: **Sat Jan 05, 2008 1:16 pm**

912 exhaust cracks
I had a 80hp Cheetah which on 127hrs cracked no4 exh pipe.At 145 hrs no 3 cracked.With the new owner no 4 again cracked on 200hrs. I currently fly a 100hp Tecnam which cracked the pipe out of the silencer after 14hrs. There is a slight prop vibration when throttling back between 4000 and 2000rpm on the Tecnam.The Cheetah has a 3 blade Warp drive while the Tecnam has a 2 blade woodprop.Any advice please?

Posted: **Sat Jan 05, 2008 5:05 pm**

Standard Rotax exhaust?
If so, that's normal. They are crap.
Mine is made in E Europe somewhere, sourced from AC Spruce.
130+ hours, no cracks.

Posted: **Sun Jan 06, 2008 1:24 am**

You will probably find that the exhaust is stainless. This is a major problem due to work hardening. My Airborne XT912 started with a stainless exhaust and after around 60 hours cracked.
They replaced no charge with the mild steel ceramic coated.No more problems :D

Posted: **Sun Jan 06, 2008 4:24 pm**

The exhasut is also liable to crack if you have wrapped it in heat resistant bandage

Posted: **Sun Jan 06, 2008 9:58 pm**

Morph wrote:The exhasut is also liable to crack if you have wrapped it in heat resistant bandage

Hi Morph, why is that pse ?

additional heat latency ?

I have about 60% of my pipes bandaged up.. thought it kept the heat away up 'top' ..

Cheers Ian

Posted: **Sun Jan 06, 2008 10:32 pm**

I was warned against doing it by a guy who runs Cowley Performance Exhausts in Cape Town. Apparently the stainless steel cannot dissipate the heat and becomes brittle. As a result it cracks very easily.

Guys in the boating world have used it extensively to reduce the engine bay heat have told me the same thing.

Due to the close proximity of my exhaust and radiator hoses I have opted to bandage the hose, which is rubber and only get's to 90deg as opposed to the exhaust that get's to 800deg C

Posted: **Mon Jan 07, 2008 5:31 pm**

Thanks for that info Morph, makes sense..... now...

Anyway I will leave mine as it is for now and watch it, if one cracks I will dig up this posting and advise all.

Cheers Ian

Posted: **Sat Jan 12, 2008 8:26 pm**

Ian, one that was all bandaged up like yours, broke on a Kalahari Bundu Bash. It had the properties of very thin cast iron. The welding job was very difficult, as the ONLY welder was BIG and the ONLY welding rod available for miles and miles around was about 4mm thick. Imagine pulling a prickly-pear thorn out og an elephant`s ass wearing boxing gloves. That was a bastard of a welding job.

:D :D :D :D