Replacing #4 cylinder baffles

[Steve]

Background: RV-9A with an ECI O320 first flown in May 2008

I noticed 2 cracks in my #4 cylinder baffle at about the 200 hour mark. The cracks appeared to begin at the widest part of the nutplates where they contacted the inside radius of the aluminum baffle. Subsequent inspection also revealed a tear in the left aft case baffle where it wraps around the bottom of the cylinder barrel. I marked the progression of the cracks over the next 100 hours with a black Sharpie, visible in the photos below.

Working with Vans Engineering and Parts dept, I ordered the following parts:
CB906A left aft case baffle
CB705A aft baffle #4
CB705B oil cooler brace
CB1004A cylinder 4 baffle
CB1004C stiffener
CB1003C doubler
CB1004B doubler
FF709 doubler
FF713 spacer, oil cooler
CB706B spacer, make from AT6-058x3/8
MS?????-4 steel lock nut
OP-44 drawings

Note many of the part numbers are the new design parts and a few are RV10 pieces. The new "revision C" baffles fit the engine like a glove and are also a different aluminum alloy from both prior designs. The new parts are 5xxx series aluminum. The drawings are also RV-10 style isometric view with instructions on the same sheet. I chose to stick with the "safety wire inside the tube" method to tie the cylinder fore/aft cylinder wraps together. New design uses bent and threaded rods for that purpose.

Here's a few pics of the process:
http://s871.photobucket.com/albums/ab273/Stephenf26/

Total time: 16 hours
Total cost: $65.00

[Steve]

NOTES

The plans locate the FF713 oil cooler spacer 3/8 inboard from the edge of the CB705A. I chose to shorten that distance to 3/16 to position the nutplates away further outboard from the fillet on the CB1004A.

You'll need another tube spacer (5/16 long) and a longer AN3 bolt where the right and left aft case baffles overlap and attach to the accessory case mount bracket. This is due to the relocated left aft case baffle (CB906A).

[N941WR]

Steve,

Do you have any pictures of the old baffle as it was installed?

If the baffles are tied to two cylinders or one cylinder and the case, they will crack because the cylinders move independently.

If you are installing the new baffles exactly same way they were and they were installed wrong, the new baffles will crack again.

[Steve]

Bill. Thanks for your thoughts. I've been following your rebuild progress closely.

The #4 baffle assembly was and is attached to the engine in the recommended method, i.e. 2 screws nearby the valve cover, 1 bolt under the engine mount vicinity, and 1 bolt to the accessory case mount. Believe me, we've beat this subject to death here in the hangar concerning movement of the cylinders in relation to each other and the crankcase. Vans does have us slightly oversizing the bolt holes to allow the baffles to "float".

Because of this 4 point attach method, it seems to me a flexible baffle assembly is better than a rigid setup. Hence the factory's current use of 5xxx series aluminum. I know another RV owner who beefed up that outside corner so much that the plane could almost be lifted off the ground using the oil cooler. I'm not sure thats a good idea either. Another guy used 7xxx to add a doubler angle inside the corner. It fractured lengthwise during the next flight.

[N941WR]

Steve,

That's a bummer, I was hoping for an easy solution.

When I put the baffles on my O-290 I brought a piece of AA from up by the inside corner of the cooler to the doubler at the top-front of the #4 cylinder. (This hole was not used by the O-290 because the screw holes are in the 2 & 4 o'clock positions on this engine.)

What I found after the 250 hours was that nothing had cracked.

Here's a picture of what I'm talking about. Granted the O-290 is much smaller than what you have but something like that might help.

Good luck!