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Baffling

ERJDriver

Well Known Member
Question for the people smarter than me. Didn’t build my 8A, the lower cowl has no silicon baffling material to seal it to the aluminum baffling material mounted to cylinder 1/2. These cylinders run about 20-30 hotter in the climb. Is this why? Cooling ramps are installed in the top cowl and that baffling is new before I bought her

It’s just the lower cowl lip sitting on top of the aluminum, how much cooling/drag am I giving up?
 
Yes, the cowl inlets where the lower cowl sits on the baffling attached tot the front of cylinder 1/2.

Not my pic but here is an example of what I don’t have
 

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Well, ya, that's not going to help!!! A multi square inch leak from the upper (high pressure) to lower cowl. I am surprised you can maintain any decent CHT at all.
 
Question for the people smarter than me. Didn’t build my 8A, the lower cowl has no silicon baffling material to seal it to the aluminum baffling material mounted to cylinder 1/2. These cylinders run about 20-30 hotter in the climb. Is this why? Cooling ramps are installed in the top cowl and that baffling is new before I bought her

It’s just the lower cowl lip sitting on top of the aluminum, how much cooling/drag am I giving up?

Get yourself a copy of OP40-14 which is the baffle installation instructions and drawings. Should have baffle seal material on that lower cowling that will lay over the bottom ramps. That will definitely reduce your CHT’s on cylinders 1 and 2.
 

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I don’t have any baffling material on my lower -8 cowl. The engine sheet metal baffles fit pretty tightly to the lower cowl with just a minimal gap. It is kind of a pain to get on but I figured out just the right amount of leaning, tongue wrist and stretching and of course a small amount of cussing to get it on. It’s not really that bad now that I know the right technique.

There was a dramatic effect on temps when I installed the upper inlet ramps which were not on the plane when I got it. The engine always had pretty high CHTs with #2 always about 20 degrees hotter. I had to pay attention on climbout but now with the upper inlet ramps installed I have no issues and can climb out on a hot day and not worry about temps, even at lower climb speeds. My CHTs are all normal now within about 5 degrees of each other. I also did a lot of sealing around the engine where I had some significant gaps.

I know a couple RV-8 guys and don’t remember seeing baffling material on their lower cowls.
 
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I have an A so the stupid nose gear is what makes it difficult. I guess I can try and tape them off and a what happens. I also don't have the material behind the spinner on that baffling.
 
Not having baffle seal material on the baffles behind the spinner can be a huge pressure leak, especially if you have the specified 3/8” - 1/2” gap between the metal baffle and the top cowl surface.
If you install the seal material on the cowl cooling inlets, you’ll need to trim the metal ramps back to give you about 1/4” or slightly more clearance from the cowl lip to allow you to get the lower cowl on. The surface of the ramp at the forward end should also be ~1/16” lower than the cowl lip to allow the seal to lay flat on the inlet ramp. If you can get that OP plans drawing as others have said it will help.
I just finished my baffle install on my RV6 yesterday so it’s fresh in my mind. I’ll try to remember to take a couple pics today, so you can see how I did my seals behind the spinner. There’s more than one way to skin this cat, but it has worked well for me on my other builds.
 
Here’s a picture of the seals behind the flywheel when I was installing them per the baffle kit instructions. I ended up installing nut plates to make it easy to replace the seal material in the future. The more air leaks you seal, front and back, the better your temperatures will be.
 

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Yes, the cowl inlets where the lower cowl sits on the baffling attached tot the front of cylinder 1/2.

Not my pic but here is an example of what I don’t have

Well, it's easy to fix.

Yep, it's possible to get acceptable cooling even with a bunch of huge leaks. Look at nearly every old GA bird...giant gaps at the front for alternator belts, flap seals long dead and rock hard, etc.

I am reminded of the old Dear Abby advice...any girl can get married if she sets her sights low enough.
 
Plenum

Or you can get really carried away and do something like this...:D
Inlets are sealed to the plenum inlets with a neoprene sock. Plenumnis sealed all the way around with an additional RTV impregnated strip of fiberglass. Cylinders are sealed to the baffles with RTV impregnated fiberglass. A few more holes and it's fully sealed.
20220514_074653.jpg
 
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Baffling material

Tom,

Don’t buy any, I have some you can have for the shipping cost. I just finished an engine overhaul and put in a new baffling sheet metal kit from Vans. I have everything done and the engine is broken in now and running well so I won’t need any of the left over baffling (and this is my last airplane).

All I ask is you take what you need and pass along to someone else that might need some- pay it forward so to speak.

PM me for details
 
I would like to pick up this thread and ask for some input.

I have an RV-6 with O320 H2AD. I bought the plane; I'm not a builder. I've had the airplane a few years but have not flown it much as it was having some work done on the panel the past 18 months.

I've been flying now for about 20 hours and have been experiencing cooling issues. Oil temps are often in the 210+ range when doing pattern work, touch and gos. I have seen it approach 230 on hotter days, 85-90 f. I haven't paid enough attention to CHTs, but I do recall seeing temps in the mid 400s. I have my max CHT alarm set at 450 and I think it has gone off once during a takeoff climb, but then dropped enough to go off. I will be paying more attention to these numbers in the coming days.

I've read numerous threads on baffle seals, and I've taken some pictures of mine with the upper cowl off. I'm thinking I may need to do some work on my baffle seals. There are quite a few gaps between the seals and the aluminum in between the rivets. There are also holes in the rivets themselves, and you can see right through them. Parts of the baffle seals are wavy and don't look like they could be providing a very good seal.

One other concern I have is that it looks like one of the vertical rows on my oil cooler is blocked. From the back side, I count 8 rows, but looking through the air entry hole in the baffle, only 7 can be seen. Is this a mistake in the build? Could it cause high oil temp issues?

Please see the pics, and any input would be appreciated.
 

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I would like to pick up this thread and ask for some input.

I have an RV-6 with O320 H2AD. I bought the plane; I'm not a builder. I've had the airplane a few years but have not flown it much as it was having some work done on the panel the past 18 months.

I've been flying now for about 20 hours and have been experiencing cooling issues. Oil temps are often in the 210+ range when doing pattern work, touch and gos. I have seen it approach 230 on hotter days, 85-90 f. I haven't paid enough attention to CHTs, but I do recall seeing temps in the mid 400s. I have my max CHT alarm set at 450 and I think it has gone off once during a takeoff climb, but then dropped enough to go off. I will be paying more attention to these numbers in the coming days.

I've read numerous threads on baffle seals, and I've taken some pictures of mine with the upper cowl off. I'm thinking I may need to do some work on my baffle seals. There are quite a few gaps between the seals and the aluminum in between the rivets. There are also holes in the rivets themselves, and you can see right through them. Parts of the baffle seals are wavy and don't look like they could be providing a very good seal.

One other concern I have is that it looks like one of the vertical rows on my oil cooler is blocked. From the back side, I count 8 rows, but looking through the air entry hole in the baffle, only 7 can be seen. Is this a mistake in the build? Could it cause high oil temp issues?

Please see the pics, and any input would be appreciated.

I also have the H2AD engine in my RV-3B. I never see greater than 390 CHT or 190 oil temp in summer 90+ deg. I even have air blocked to the oil cooler or it will be less than 180 deg, otherwise.

I would start by replacing your baffle seals with new material. They look like they may not be sealing with the cowl. I would look at baffle/cowl interface at the fuel pump. You could be leaking there. I would look at the latest build instructions for baffle/cowl installation and make sure appropriate steps were followed during construction (ie, gap between top of baffles and top cowl). You may need air dams on cylinders 1 and 2 for adequate airflow to cylinders 3 and 4. It will probably require some experimentation, it did for me. Look at photos of other installations for ideas.

Temperatures you are seeing are not normal. Good luck.
 
Jim, you have it right. New seals would be a big improvement.

The upper cowl tells a lot. I've circled some areas. The red circles show smudge tracks, areas with dirt and soot stains where lots of air has been escaping the upper plenum through seal areas which fit close, but not close enough. Green is showing wear areas, places where the seals are contacting the upper cowl, a good thing. Magenta areas have no contact or soot marks. The existing seals in those areas are pretty much useless.

The black fiber reinforced seal material is a GA standard, but it's not nearly as good as a conforming silicone seal.

Here's the trick for installing silicone. Typically we want it to lean inward about 45 degrees. So starting at one end of a seal strip, fasten with one rivet or cleco, the pull the strip to stretch it a wee bit and hold it while punching or drilling the next rivet location. Repeat a few times and watch what happens.

The hole in the left ramp for the fuel pump is forming a huge leak. This is one of the rare cases where a bulkhead or fill inside the ramp would block the path.
.
 

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Thinking about the earlier statement that “the aluminum baffle is close enough to the fiberglass cowl”

The rubber material installed correctly will allow the wet dog to shake without fracturing the glass or aluminum.
 
baffle seals

I've got pictures of my baffle seals here: http://www.rv8.ch/silicone-rubber-baffle-seals/

You can see the kinds of things that Dan is pointing out when the seals rub against the cowl. I will add a photo of the upper cowl to show the wear marks next time it's off.

I have excellent cooling - not sure if it's due to the seals or something else, but it's a data point. Any feedback or suggestions or comments most welcome!

IMG_6908-1024x768.jpg
 
Dan, thank you for that info. I'm going to measure it all up and order the seals. I'm going to try and tackle this job myself.

Mickey, those are fantastic pictures. Thanks for your reply. Thank you Robert and Blain for your input as well, appreciate it.
 
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