Leaning techniques for 0-540 again

[Idahomauledriver]

I apologize for dragging out an old subject again but since I just burned out a muffler on my 0-540 in my Maule I thought I would throw out my procedure for comment . I am pretty anal about leaning out the engine and once I have reached cruise altitude I set up my power settings at 21Mp and 22 rpm and then start to lean a turn at a time to reach lean. I wait about a minute or so between turns to let the EGT settle and then tweak it again until I reach peak lean and then tweek slowly to ROP 100 degrees. Generally my numbers settle at lean being around 1500 degrees,ROP 1400, CHT 310- 320. During descent I again monitor the EGT temps to keep them around 1350 making the adjustments as needed . Any thoughts ?

[willisbr]

I use a JPI 700. I have been squaring up, 22 Mp and 22 rpm, and then start to lean in moderately slow and smooth turns. 2-3 seconds for each turn. Your temps should climb gradually and predictably. When the JPI starts pointing at a certain cylinder for near peak (usually 5 for me), I start slowing my turns down as the temps catch up, but not too slow. Once I see the JPI indicate leanest, I hold down the right button and capture my hottest temp, then back off slowly to 100 cooler degrees from that number. That should give you leaned ROP. That's how I do it. I think if you are waiting a minute or so between each turn, maybe you are spending too much time at higher temps. You should be able to lean ROP within a minute or two I think. How does this sound to the rest?

[maules.com]

Generally speaking, if the muffler is burned through on the side of the can, it is because the flame trap inside has burned away so the flame from the rear two cylinders strikes the opposite side of the can
The flow from ex stacks on front cylinders on the 540 and the stacks of the O360 s are angled back through the can so heat is disipated before hitting the can.
There is a SB to remove the tailpipe clamp for inspection of the locater dowel and the tailpipe and muffler locater holes for wear and elongation every 100 hrs or annual.
The tailpipes should be removed at that inspection so as to look at the flame tube's integrity. Sometimes the far end is burnt out, sometimes it is burnt further along. It is easy to see. It can be replaced for about $50 by diegrinding the spotwelds off, removing the remaining piece and tack welding the new one in.
So far as leaning, there is a big difference between leaning the IO540 withe a JPI and an O540 with single probe EGT.
The temp spread on the IO540 can be leaned to 60 or 70 deg difference and the hottest cylinder can easily be seen on the JPI.
The O540 EGT spread is often up to 150 deg and the single probe instrument may not be on the cylinder that is leanest, or the one that is hottest. It varies with OAT, altitude and condition of the cylinder components at the suction stroke.
The result is that the carb version will normally consume 1+ gph more than the injected version.
If no ex temp analizer is fitted, leaning can be accurately accomplished by ear and watching the rpm and mp instruments as this will be related to the cylinder that is getting hottest first.
With a spread of 150 deg one can see that even if one cylinder is leaned then richened by 100 deg, another could be 50 lean.
Maybe an engine tech on here can explain it more clearly.

[Idahomauledriver]

Thanks for the info Jeremy. You insight is always appreciated. The muffler burned through at the bottom. It sounds like my target ROP should be 150 degrees.

[maules.com]

I don't think you need to run 150 ROP, that will consume alot of fuel.
First cyl to peak is not necessarily the hottest.
If you lean by ear and instruments, carefully screwing the vernier approx 10 deg per second until you hear/feel /see a power change/minor roughness, then turn vernier back in about 3 flats, you will be close to what you want. Check tailpipe outlets at end of flight for light to medium grey, not black and not white.
The flame traps deteriorate with age, vibration as well as heat, so this holed can may have nothing to do with leaning.
Getting 800 hours on your mufflers is fairly good but I imagine the flame tubes have been burnt out for quite a while.
The can gets compromised and then all it takes is a little backfire from prmature throttle retard to blow a hole.
By the way, if the cowling hole is not too large, it can be trimmed and covered with an inspection cover as when fitting a quick drain.

[a64pilot]

I'd tell you your leaning is just about perfect as it is and that it's the design of the "O" mufflers and the fact that your a lower compression engine running higher EGT's that's burring your mufflers.
An I/O I believe has constant airflow around the muffler, when cabin heat is on hot air flows into the cabin, heat off, air dumps into the engine compt. so the muffler runs cooler, but it's as Jeremy says, the flame trap is what keeps the muffler from burning through, when it goes, your muffler and maybe your cowling go soon after
O motor has carb heat, carb heat off, no air flow

[a64pilot]

first cyl to peak may not be the hottest, but it is the leanest, The hottest EGT will be on the lowest compression cyl., running compression may not be able to be determined by a compression leak down test. You want to lean from the leanest cyl when running ROP and the richest when running LOP (my opinion)

[Idahomauledriver]

Makes sense. Thanks everyone for the replies. New mufflers installed and cowling repaired better than new.