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Baffle RTV

JDA_BTR

Well Known Member
I ran into the step asking me to put RTV on to seal the gaps between the baffle and the engine. I assume that is everywhere on top where air can go out without going past a cylinder fin. There are places where the baffle does a good tight fit at the fin edges and I wonder if I really need RTV there.

Or is this intended to be mainly sealing the baffling interface to the engine CASE? If I did RTV between engine case and the baffling, along with sealing some small holes in the baffle joints, that would be pretty efffective. In that case no RTV on any cylinder, just baffle/case and some baffle corners.

Anyone have any pics with arrows of what to seal if doing it perfectly by the plans?
 
Generally, you are sealing the baffles to the case, but the objective is to close any airpaths that don't push air through cylinder fins, the oil cooler, blast tubes, or SCAT going to heaters, carb heat, etc.

Even if you don't see a gap between the aluminum baffles and the case, a bead of RTV is a good idea to eliminate relative motion between the two, preventing fretting and wear on the baffles or case.
 
Help keep that precious air going over the cylinders.

Here's part of what the plans specify, from when I placed the baffles:

Left aft baffle.



Forward baffle.



Here you can see various nooks and crannies sealed (from when I installed the control cables). Note the forward area along the forward of the crankcase, the areas around the blast tubes, prop cable and other little areas.



Here you can see the rear of the crank case sealed as well as some areas along the rubber seals (from when I riveted the upper forward fuselage skin).

 
They are hard to see and access, but . .

Don't forget to look closely at the intersection baffles between the lower cylinders. They were a huge leakage area for my factory M1B.

Edit: and . . did you check for the flashing on the through fins around the spark plugs?
 
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The sealant you want is Loctite 598.

https://www.henkel-adhesives.com/us...sealants--flange-sealants/loctite_si_598.html

Available in a 300ml caulk tubes or small squeeze tubes. In the US, Permatex Ultra Black is the same product. In additional to not being monkey butt orange, it is remarkably tough, oil resistant, and has a good temperature rating.

It's not hard to understand what you want to accomplish, which is to make sure every molecule of cooling air (1) remains in close contact to hot parts, and (2) actually gets to the hot places.

A light bulb held under the engine will highlight gaps.

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The problem with wraps is usually air leaking from the sides, which means it does not cool the area around the lower spark plug. There are a whole lot of fins down there, but they won't do you any good if the air gets sidetracked.

BTW, Lycoming places a rubber comb between the fins, which blocks some flow and often worsens the wrap fit problem.

Along the same lines, engine shops often add a bead of silicone across the baffle in an attempt to stave off chafing wear. However, if the silicone is up between the fins, it blocks flow.

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The sealant you want is Loctite 598.

The general description of the product is RTV. What makes this RTV different than the black high temp RTV from the parts aisle at Wal-Mart?

For what it is worth, I've been using the high temp black stuff from Wal-Mart/NAPA/Wherever for 20 years without any problem...
 
Dan H question ?

3M Fire barrier 2000 really sticks to aluminum well and is GRAY. Any reason not to use it for sealant ?
 
When you buy it in the can does it come with some kind of straw like WD40 does? Seems the 190ml caulk tube is the easiest to use? This comes in a lot of different packages.....
 
Forward baffle.



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The above RTV strips seem counterintuative to me. In my head the RTV that is not touching the front of the fin would bulge inside the empty space between the fins. limiting the airflow.

Not only is there one "strip" of RTV, there are 2.

Van's instructions tell the builder to do that now?
 
The above RTV strips seem counterintuative to me. In my head the RTV that is not touching the front of the fin would bulge inside the empty space between the fins. limiting the airflow.

Not only is there one "strip" of RTV, there are 2.

Van's instructions tell the builder to do that now?

If the instructions are followed, the RTV stripes will only be about .030 thick.

Enough to help prevent fretting wear, but not enough to cause any air blockage or leakage.
 
If the instructions are followed, the RTV stripes will only be about .030 thick.
Enough to help prevent fretting wear, but not enough to cause any air blockage or leakage.

I dunno 'ole buddy. If the stripes space the wraps away from the fins by .030", there's a .030" wide leak gap along the side edges.

If the goal is to stop fretting and keep all the air where it belongs, gasket the whole inner surface of the wraps.

P1250003.JPG
 
I dunno 'ole buddy. If the stripes space the wraps away from the fins by .030", there's a .030" wide leak gap along the side edges.

It is a very small amount of surface area coated with a very flexible/compressible material.

My experience is that with the wraps pulled tight it has no influence but I imagine an even coating as in your photo would be the optimal plan.

Especially if you are measuring gaps with a feeler gauge ;)
 
I dunno 'ole buddy. If the stripes space the wraps away from the fins by .030", there's a .030" wide leak gap along the side edges.

If the goal is to stop fretting and keep all the air where it belongs, gasket the whole inner surface of the wraps.

P1250003.JPG

Dan, what kind of material is that? Did you still place the aluminum wraps over the top of it?
 
Dan, what kind of material is that? Did you still place the aluminum wraps over the top of it?

From a previous DanH post: it's 9 oz glass impregnated with Permatex - put in place wet. The aluminum baffles go over this, per plans. I'm baffling my IO-360 now, and have been scrubbing all relevant posts.

SUPER thanks go out to DanH for his wonderful posts on this subject!
 
From a previous DanH post: it's 9 oz glass impregnated with Permatex - put in place wet. The aluminum baffles go over this, per plans. I'm baffling my IO-360 now, and have been scrubbing all relevant posts.

Yep, Loctite 598 or Permatex Ultra Black, same product. Roll it into the cloth between two sheets of 4 mil plastic. Cut the exact shape you wish to apply. Peel one side, stick it to the fins. Allow to cure, and only then peel the plastic off the outside.

When fastening the aluminum wraps into place for the final time, be sure to run a small bead of sealant across the the top , so air cannot flow between the aluminum and the outside of the fiberglass/silicone gasket. That would be a really useless leak.

Cylinder%20Wrap%20Sealing.jpg
 
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Hoping to add to and not de-rail this thread.

I installed these baffle/cylinder wraps on my parallel valve engine, I ended up removing them for testing etc. I can tell you they stick like you wouldn't believe on the cylinder fins, Its an amazing composite. After more flying and testing I then used Ultra Black to stick the same sheets of RTV impregnated glass I pulled off my cylinders to my lower baffles, I've been satisfied with this compromise. This undoubtedly leaks more air than DanH's method but seems to work well for my parallel valve setup.
 
Extension tube . . .

When you buy it in the can does it come with some kind of straw like WD40 does? Seems the 190ml caulk tube is the easiest to use? This comes in a lot of different packages.....

I made my own. Expanded some poly tubing to form a flare so the pressure would not extrude the tube out of the tip. Sealed with some soft wax. Started with 5/16, with a 1/4" tip.
gFaTdpZE3Sq8j9uHf0AZ4P6P5hRKiu_SF-3zTTkykY1TAfo3KgIV5Vcl3O9cIX1n_Fv7_-XF6sh0HygLM1_9_6XUsnHp6rFyi-PYMEVy2PX-ev_98MIvgk_QJusuMyuzOQvjLtD2UoXdouPmxIbwC5PzZ88VLA9xyzURAb4xSa6kqhBZ5tuPcay75Sr6s-AkGFrlIgPcFsHo-3sB8dcoTU5I3plE6O00CVMEJnlHEiowaB-TgvgNPxCmhZZ7ed_Aa0xCenrpIAU9X0DjM7G0qQKuICetLrdl1UyRFlOmkx0NYCnAumZO1HKbb7D_SSsFczgLyZ89FdN6P6b8mRqYdUjtuCRi4h-h1rJdT0v5TfYF6k6Lk5UpVBdQTBRs1Ytv5DrEcKeMdkp7zBG0TuqEUPNTnEaI4eQhJVRIt6N3OFriChKKdGhEzP89omx-i9t3kjVmbSUVlhVPoBS_biDag4r_VnmSi2WT1APv6HGChId-FlQ2Ml--vpuvY3Db1JFhd_hzgbxbQciJDPw9U2h7H7ok4RdIVcxq9Bb06G7NkreXQYl-BNe4W7NKp2zX9BVJVOiiFBnRPRmnpAd9Je4JKg0nW901fsQAjwWMOaWDwefuG33o3da1CCXzbn2iztzjAnI0EfRCJrIBESppMdaLwLCu6i-Q62OI0lq-PO5vK3I2BLSWNxwSEIEq=w700-no
 
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It is a very small amount of surface area coated with a very flexible/compressible material.

My experience is that with the wraps pulled tight it has no influence but I imagine an even coating as in your photo would be the optimal plan.

Especially if you are measuring gaps with a feeler gauge ;)

That's a fair point, and I'm not gonna bore everyone with a homily about "better". The factory crew has the unenviable task of developing methods and instructions for everyone, which includes the least capable builders. Then they get to explain it repeatedly on the help line. The prescribed stripes (to prevent wear, not seal) are simple, and if they can get the builders to actually fit the baffles tightly, it's good enough. Airplanes shall fly. Grins will be seen.

As for us nut cases, zero leakage is the goal. It's a mental illness with a justification ;)

BTW, it's important to differentiate between merely gasketing the standard cylinder wraps, and extending the glued-on gaskets further up and around the cylinders and heads. The first is just improved sealing. The second has a bunch of interesting effects, some of which, depending on application, are quite experimental.

Regardless of which path is taken, please, take the time to fit the baffles, not just drape them on the engine.
 
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The factory crew has the unenviable task of developing methods and instructions for everyone, which includes the least capable builders. Then they get to explain it repeatedly on the help line. The prescribed stripes (to prevent wear, not seal) are simple, and if they can get the builders to actually fit the baffles tightly, it's good enough. Airplanes shall fly. Grins will be seen.

Exactly

Testing has shown that the methods described in the latest construction manual work quite well and are achievable by amateur builders.

Can it be optimized or made better? In many cases the answer is yes, and done on purpose so the true experimenters have something to
"experiment" on ;)
 
If the goal is to stop fretting and keep all the air where it belongs, gasket the whole inner surface of the wraps.

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I used this process on my Whisper Quiet TCM550 a few months ago. Now the dang 'normally over-temping' engine runs with CHTs around 300 or LESS most of the time. Had to block off some of the oil cooler too as the oil went to 160 or so in cruise.

Now my steady work is modifying the rubberized stuff to bring the temps up to 320 or so. Very odd, but the front cyls behave normally temp-wise, but the center and aft cyls are the cold ones...:confused:

BTW I did not 'cover' the rubberized stuff with any aluminum stuff. I don't think it will blow off - but I could be wrong...stay tuned.

I guess I need a house call from Dan...I must have done something wrong.
 
Now my steady work is modifying the rubberized stuff to bring the temps up to 320 or so. Very odd, but the front cyls behave normally temp-wise, but the center and aft cyls are the cold ones...:confused:

A few piccolo tubes might lead to enlightenment.

BTW I did not 'cover' the rubberized stuff with any aluminum stuff. I don't think it will blow off - but I could be wrong...stay tuned.

I assume you mean glass wrap extending above the 9 and 3 o-clock plane. Not likely to blow off there, as static pressure pushes it toward the fins. Underside of the cylinders? Tell me more.

I guess I need a house call from Dan...I must have done something wrong.

You got beer?
 
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