Inter cylinder baffles

[Mconner7]

I am still suffering fairly hot CHT’s on my recently (35 hours) rebuilt O-540. On trip yesterday at 5000’ I tried to run 75% (172 KTAS) but had to run 17 gph to keep #6 below 400 degrees. At 21”/2300 I can get the ff down to 11 gph at 160 knots and be at 385 CHT.

I read this from Savvy Aviation but I don’t think our Lycoming inter cylinder baffles are location specific?

https://mailchi.mp/savvyaviation.co...Mw3xO-d1EpBxDvdRh50rDEmy5AhMXO0_9dcW-ztScFEh4

 

[DanH]

I read this from Savvy Aviation but I don’t think our Lycoming inter cylinder baffles are location specific?

Maybe, maybe not.
.

 

[mahlon_r]

They are not location specific unless there is a mod to one to accommodate plumbing or some other location specific use like a hose from the servo to flow divider. It would be very obvious if one was different than the others and thus location specific. If nothing is plumbed between the cylinders then the IC baffles would not be location specific.
Good Luck,
Mahlon

 

[Marc Bourget]

Dan's observation requires more detail from the original observer.

What differs from front to back and why does that make a fluid dynamics difference?

 

[lr172]

Maybe, maybe not.
.

One of those baffles has a hole /grommet in it for the -4 line from the servo and it goes in the 1/3 position. It is otherwise the same as the other 3. That article references a continental engine with no relation to a Lyc.

 

[lr172]

Did you seal up the IC baffles to the case? Mine had some pretty large gaps that required filling with RTV. Not easy to get to but makes a difference. Did you reseal all of the other baffling back to the case? Don't mean to offend, but have seen more than a handfull of planes that don't do this or don't do it well enough. They seem to keep Alan in business by buying cowl flaps. I would also check the fit of the lower baffling tabs that wrap around the bottom of the fins. Most have large gaps, as the builder doesn't tweak the angles to make them lay flat against the fins. They tend not to fit that area well as they come out of the box, though they don't need a lot of adjusting.

 

[Mconner7]

Did you seal up the IC baffles to the case? Mine had some pretty large gaps that required filling with RTV. Not easy to get to but makes a difference. Did you reseal all of the other baffling back to the case? Don't mean to offend, but have seen more than a handfull of planes that don't do this or don't do it well enough. They seem to keep Alan in business by buying cowl flaps. I would also check the fit of the lower baffling tabs that wrap around the bottom of the fins. Most have large gaps, as the builder doesn't tweak the angles to make them lay flat against the fins. They tend not to fit that area well as they come out of the box, though they don't need a lot of adjusting.

Larry,
No offense at all. After owning a Tiger for 10 years, baffle sealing in second nature. I sealed all the baffles to the case and all the inter cylinder baffles at the base while the motor was still on the stand. It was much easier then than after installed. I am considering retarding the timing a couple of degrees to see if that helps…..

 

[BillL]

Mark, this is a very specific question without much context. The Lyc intersection design is substantially different than the Conti. Also the Lyc parallel valve design seem to have less "connection" to the barrel cooling that I would have thought.

Caveats apply here, but if you have just one cylinder that is way off, not a bad plug, not A/F, and more than 40F difference, then look at the opening on the bottom of the head. If everything else is equal, then that can alone make a different as it can become a relative restriction.

The engine still has to have all the leaks addressed including oil cooler and have a good pressure drop from top to bottom.

Things like timing, advance, gaps, etc all still have to be in the realm of consideration until the numbers guide to something significant.

 

[lr172]

Larry,
No offense at all. After owning a Tiger for 10 years, baffle sealing in second nature. I sealed all the baffles to the case and all the inter cylinder baffles at the base while the motor was still on the stand. It was much easier then than after installed. I am considering retarding the timing a couple of degrees to see if that helps…..

Timing doesn't make sense, as it should affect ALL cylinders, not just one. How old are the mags? Inside is a cap and rotor, just like 70's vintage autos, with the exact same issues. Ionization build up or carbon traces can let just one cyl spark earlier than the others. Given the break in, I am assuming you are still running ROP. Have you swept the mixture to peak to see if that one cyl is running leaner than the others? Could be a tiny piece of trash in the injector.

Larry

 

[Mconner7]

Timing doesn't make sense, as it should affect ALL cylinders, not just one. How old are the mags? Inside is a cap and rotor, just like 70's vintage autos, with the exact same issues. Ionization build up or carbon traces can let just one cyl spark earlier than the others. Given the break in, I am assuming you are still running ROP. Have you swept the mixture to peak to see if that one cyl is running leaner than the others? Could be a tiny piece of trash in the injector.

Larry

Larry,
I have an O-540 with a carb so poor fuel distribution is not surprising. The EGT’s seem very close to each other and rise fairly evenly with leaning.
#6 is about 20-25 degrees hotter than the others. The mag is about 700 hours since new and 200 since last rework. The other side is a SureFly Sim. I have had several experienced folks look over my baffles. I have another mag, I will rebuild it and try it out.

 

[Tommy123]

How do you have the Surefly set up? Fixed timing of advanced mode? Also make sure the dip switches on the Surefly are in the correct position for your engine.

 

[Kyle Boatright]

Is your Surefly running the fixed or variable timing? In other forums, I've seen numerous reports of high(er) CHT's with the Surefly running variable timing.

 

[Mconner7]

Is your Surefly running the fixed or variable timing? In other forums, I've seen numerous reports of high(er) CHT's with the Surefly running variable timing.

Kyle,
It is variable, that’s the main reason to use it over a fixed timing mag. The idea is that it will not advance timing at high power settings where my motor runs hot. It’s magic is at low MP when it makes the engine more efficient.

 

[Kyle Boatright]

Kyle,
It is variable, that’s the main reason to use it over a fixed timing mag. The idea is that it will not advance timing at high power settings where my motor runs hot. It’s magic is at low MP when it makes the engine more efficient.

You might try resetting it to the fixed timing option to see if that changes anything. It certainly won't hurt anything other than cost you an hour or so to reset and reinstall it and another hour to return it to the variable advance setting if you don't see any benefits from fixed timing.

 

[Marc Bourget]

Asked because it wasn't mentioned earlier in the thread and there will be some not familiar with the following "condition."

I've seen head casting irregularities mention on this forum before.

Have you looked at the inter-fin spaces of the particular cylinder?

I have a O-290 cylinder that one of the fin spaces between the valve "towers" was blocked in casting. All the factory did was drill a single (approximate) #30 drill hole - which provides virtually no cooling flow.

FWIW

 

[lr172]

Larry,
I have an O-540 with a carb so poor fuel distribution is not surprising. The EGT’s seem very close to each other and rise fairly evenly with leaning.
#6 is about 20-25 degrees hotter than the others. The mag is about 700 hours since new and 200 since last rework. The other side is a SureFly Sim. I have had several experienced folks look over my baffles. I have another mag, I will rebuild it and try it out.

poor mixture from the carb generally affects more than one cyl. Don't have any experience with carbs on 6 cyl, but on the 4 cyl, it tends to have two equal AFRs on the pairs, with the big difference between the pairs. Are these new cylinders or did you have the old ones overhauled? the uniformity of the rise doesn't help much. Would be better to know the # of degrees between the ROP setting and the peak setting for each cyl. Then we could determine if mixture is the culprit.

I the guy doing the rework was any good, I kind of doubt that 200 hours is enough to create the issue I mentioned on the mag. But no guarantee that he didn't skip steps. This is a low probability IMHO.

Do you have an air dam in front of #2? Where is #2 CHT relative to the others. Mine look something like 1/2: 325, 3/4: 310, 5/6:335. #6 may be a few degrees hotter than #5. Mine works pretty well, but have plenty of variance. Someday I plan to experiment with 3/4 dams to even things out, but the current spread is of no concern to me. It would be helpfull to see the full spread of CHTs for the scenario we are talking about.