odd exhaust sounds

C

cyav8r

New member
My airplane has been sounding a bit sick lately and we have been unable to identify the cause. Basically it’s popping and sounds a bit like an old farm tractor we used to have.
If you’d like a listen we taped it because I can’t really hear it in the cabin and the noise seems to be very directional with the tail pipe: http://www.iac15.org/725JM/SuperD_noise.htm

We first though it was an exhaust valve(s), but compression checks hot and cold have all been normal in the upper 70s. Then we thought it was a sticking valve, but after inspecting the entire valve train nothing was found there either. We have verified the mag timing and fuel flow to each cylinder, and there has been no metal in the oil or oil filter. I’m also not seeing anything out of the ordinary on EGT, CHT or fuel flows in climb/cruise and power seems to be normal as well.

So could it be the internal muffler baffling breaking down? We have pulled off the muffler to look for leaks (nothing visible) and to see if anything was loose inside (no rattles), but put it back on since it appeared to be fine. It looks good on the outside but I can’t really see much inside to know what going on in there.

Any other ideas to try or places to look before I send off for a new muffler?

Thanks

Paul
 
Hi Paul,

I don't know what your problem is, but if you even suspect it to be your muffler, get it looked at right away. My only forced landing was due to the baffles breaking off and blocking the exhaust. The engine quit once prior to the forced landing, I was in the traffic pattern and conditions were ideal for carb ice. I landed, ate lunch, it fired right up. I figured the ice had melted. What had happened was the baffle parts were jarred on the landing and the exhaust cleared. The next time it happened, I was about 500 AGL. It quit with out any warning. Just like turning off the mags. I suspected bad gas, but an A&P friend insisted that I check the muffler. Bingo!

Bill
 
this is kind of like a doctor diagnoising a patienent over the phone, but what i THINK i am hearing is an exhaust leak at the manifold. double check all the exhaust gaskets and make sure the exhaust manifold bolts are correctly torqued. i chased a sound very similar to that on an old champ. turned out to be a warped exhaust flange. once it was surface ground flat again, the system sealed up nicely and the noise went away.
 
I agree with cfiiguy. It sounds like its coming off a single cyl./manifold assy. Check the manifolds and cyls. under a good light (sunlight) and mirror. Eric
 
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