The Cessna 120-140 Association Forum

My 140 has the original straight pipe exhaust with the triangular support bracket that attaches near the exhaust outlet. The bracket was cracked when I bought the plane and had obviously been welded back several times judging by all the boogers on it. I got a replacement and it cracked within 10 flight hours. Any ideas on what to do, or how to prevent this from happening? I like the originality of the exhaust and don't want to convert to the 150 style.

That bracket is supposed to clamp down on the heat muffs which are supposed to be isolated from the exhaust stacks by asbestos. This may provide enough cushion to alleviate the cracking. Another thing that might cause cracking is if the bracket doesn't fit right and is stressed to fit.

I have the same exhaust and my bracket was repaired once, at the convention in Ona. No problems since then! (That was more than a few years back...)

I put some fiberglass insulation between the bracket and exhaust but that didn’t seem to be enough. Mind does seem to be pretty tight but I’m not sure how I could change that. I’d either have to bend the exhaust or extend the bracket.

Mine cracked a long time ago and has been OK since after being welded. Plenty of cushioning material helps. Any kind of heat resistant material will work. I've used asbestos looking tape, also a roll of black sealing tape from those "Green Egg" smokers also works. Metal to metal contact should be avoided.

6277 wrote: ↑Mon Nov 09, 2020 6:55 am Any kind of heat resistant material will work.

Google "header wrap".

Just a thought - when were your engine mount rubbers changed last? Possible root cause of the whole situation, plus good welds and not so good welds may leave the metal brittle and subject to next failure. Welds such as this should be "normalized" - some welders may not understand the science. 2c

I don't have much experience with this . All suggestions are correct -- as much vibration absorbing material 'twixt muffs/pipes/clamps sure helps. Too, reducing vibrations via good rubber mounts that are "torqued just right" and even prop balancing can help. Good welding...tig maybe(?) is important as noted above -- brittle here will crack. One of our CA members, Still Chase, fabricated a bracket that included "spring-cushioning" clamps & he reported good non-cracking experience -- I'm not sure, but his plans may be in our library (If not I may be able to retrieve a copy from "somewhere" ). FWIW, Wag Aero usually has a small stock of brackets that mirror the Cessna part well & are priced "reasonably". Mac

2066 wrote: ↑Mon Nov 09, 2020 5:39 pm One of our CA members, Still Chase, fabricated a bracket that included spring-loaded clamps & he reported good non-cracking experience -- I'm not sure, but his plans may be in our library (If not I may be able to retrieve a copy from "somewhere" )

Still Chase's exhaust bracket.

I repaired my original which promptly cracked and replaced it with the wag aero part. Am I running the risk of cracking my exhaust pipe running it in the meantime? Also any recommendations on dynamic balancing with a skull cap?

wccborn wrote: ↑Mon Nov 09, 2020 7:12 pm I repaired my original which promptly cracked and replaced it with the wag aero part. Am I running the risk of cracking my exhaust pipe running it in the meantime? Also any recommendations on dynamic balancing with a skull cap?

This (pic) gives some idea of where/how to place weights on our props. RE the Wag Aero bracket, it seems to work as well as the OEM as long as it's "cushioned" as discussed above. Just curious -- what kind of clamps are you utilizing with it? I do recall that some of the Wag brackets had the top attach hole bored larger than 1/4", so bushing there helped ensure it didn't move too much up there. Related: I recall a few years back visiting with a couple of 140 owners at OSH -- one had no bracket at all & said that (so far?) there was no exhaust cracking issues. Another only had a connecting link from one exhaust muff tip to the other -- the top part of the "triangle" was totally missing. He, too, said no cracking...so far. I never saw either again, but doubt seriously that either lasted for long without some cracking. Exhaust cracks can often be very hard to see. My current exhaust ("repaired") is made with significantly heavier SS than the OEM thin walled & the repairer opined that these would never crack, even without bracing -- not worth taking the chance to prove either way for me. . A final note, I have a close neighbor with a 120 and he just had to repair the cracked bracket for his 150 exhaust & I know of others, so it just may be a fact that vibration is constantly on the attack "looking" for something to crack & just something we have to deal with? . Mac