Engine baffle cracks

Has anyone experienced cracks in the left rear baffle bulkhead with the oil
cooler attached? I've been told that I should build a brace, strut, from the
top of the cooler inboard side 45* angle up or over to a forward crankcase
half bolt on top of the engine. Any comments or experience on this.
Ted

the very least-- install flat washers on the alum tubing type spacers-- if you don't already have them.

dan C has good info on his site. you have any picts?

Common problem

Ted Farmin said:

Has anyone experienced cracks in the left rear baffle bulkhead with the oil
cooler attached? I've been told that I should build a brace, strut, from the
top of the cooler inboard side 45* angle up or over to a forward crankcase
half bolt on top of the engine. Any comments or experience on this.
Ted

Click to expand...

Yes there are all kind of doubler and brace schemes. I like moving off the baffle. I hate Vans firewall kit because it is terrible for cooling there is a proper way to do it, and that ain't it. I'll show you how to do it if you are interested.

If you want to stay with the baffle mount you can install a diagonal brace over the cylinders going from the inside corner of the baffle (joggle) and to an engine case bolt (two fwd of where the lift strap is). Here is another idea:
http://www.rvproject.com/20040721.html

Another brace method used separate or together with the diagonal above is extending the vertical angle in the baffle corner (left rear where I assume you have the cooler #4 cylinder). You can run a diagonal to the aft cooler flange. See link (age down):
http://rv8a.tripod.com/plenum.html

Don't forget washers on spacers or better angles nested in the cooler flanges.

G

Brace the OIL COOLER, not the baffle

gmcjetpilot said:

If you want to stay with the baffle mount you can install a diagonal brace over the cylinders going from the inside corner of the baffle (joggle) and to an engine case bolt (two fwd of where the lift strap is). Here is another idea:
http://www.rvproject.com/20040721.html

Click to expand...

In my opinion the absolute KEY if you decide to use a brace, is that the brace must attach as directly as possible to the oil cooler itself. If you simply brace the baffle, still allowing even a minute amount of flex where the oil cooler attaches to the baffle, you can expect to see cracking.

As long as your brace ties the oil cooler itself to the engine case or cylinder boss or what not, then you should be OK.

FWIW, I had a brace running from the baffle to the engine, and I still had cracking occur. It wasn't until I braced the oil cooler itself that I solved my baffle cracking problems.

I have had over 500 hours on my current setup with not a single crack or issue.

To illustrate this with photos...here was my initial setup, with the brace attached to the BAFFLE, not the oil cooler:



That design failed in two ways -- first of all, the "crimped end" stainless tubing broke at the crimp. But more importantly and more to the point, this design braced the baffle, not the oil cooler. There was still flex at the back baffle wall and it cracked like crazy.

Enter the next and "final" design:



The key here is that this brace totally immobilizes the inboard edge of the oil cooler. The baffle happens to be braced as well, but the key is that the oil cooler cannot flex the baffles.

An experienced builder once told me: "If you can push and pull the plane around by the oil cooler, you done good. If yanking on the oil cooler causes any visible flex on the baffles at all, you will eventually see cracking." I have lived by this credo since.

If I were starting over, I would probably mount the oil cooler on the engine mount, and provide a short semi-flexible duct to it...alleviating the baffles of any stress that the oil cooler causes. The oil cooler will be completely immobilized by virtue of being attached to the engine mount. No stress on the baffles. No heat conduction, or at least less heat conduction, from the HOT cylinder head to the adjacent oil cooler. At least that's what I tell myself I will do next time.

But I am happy with my current setup, and the baffles haven't cracked at all in the oil cooler area since redesigning it with the brace that ties directly into the oil cooler.

)_( Dan
RV-7 N714D (683 hours)
http://www.rvproject.com

100 hours isn't the best indication

Rick,

Mine failed around 125 hours. I know at least one other builder who used a similar design (strut bracing the baffle, not oil cooler) who had a failure around 110 hours. 100-150 hours seems to be the magic number for failures.

Anyway, you mentioned an .063" reinforcement at the corner. Well, I used two .125" reinforcements...the 1/8" thick corner reinforcement:



and then the 1/8" thick C channel mount:



And get this -- the rear baffle wall itself is made out of a sheet of .040" riveted to .063" aluminum. It's pretty beefy!

And at the "inner corner" where the oil cooler baffle face jogs forward, I used a combo of .125" and .063" to form that corner:



And to top it off, I ran an .063" thick angle laterally *below* the oil cooler, all the way across that baffle wall.

Overkill? Perhaps. But for a few extra ounces, I am fairly confident that this design will take me to TBO. Again, I have 683 hours on the plane, with well over 500 hours on this latest design. I'm not saying it won't fail, just saying it has stood the test of time & abuse SO FAR.

)_( Dan
RV-7 N714D
http://www.rvproject.com

Oil cooler flange failure

Rick,

I also noticed in your photo that you don't have any washers between the tubes which run between the oil cooler flanges and the flanges themselves. I had an oil cooler flange failure as a result of this. In my opinion, it's really important that you have washers at the tube ends to distribute the load in this area. Here's a photo:



Here's what happened without the washers:



)_( Dan
RV-7 N714D
http://www.rvproject.com

dan said:

.............noticed in your photo that you don't have any washers between the tubes which run between the oil cooler flanges and the flanges themselves....................important that you have washers at the tube ends to distribute the load in this ......www.rvproject.com[/url]

Click to expand...

Thanks for the heads ups Dan. I will insert washers in those locations immediately. As you well know, that oil cooler metal is very soft. Regards the baffling.....at present my inclination is..."If it ain't broke, don't fix it". However, if it does experience cracking or other notable failure, I will document the event and pass the information along.

Rick

Radius filler

In stead of single washers consider a thick piece of aluminum the full length of the cooler flange. You file the edge of the this aluminum doubler to NEST into the radius of the cooler flange. This spreads the load out and SHEARS it into the flange verses bending the flange. Washers still apply local stresses and the majority of the flange is not effective. (yes I was a an aerospace stress or structures engineer ) G

gmcjetpilot said:

In stead of single washers consider a thick piece of aluminum the full length of the cooler flange. You file the edge of the this aluminum doubler to NEST into the radius of the cooler flange........... Washers still apply local stresses and the majority of the flange is not effective. (yes I was a an aerospace stress or structures engineer ) G

Click to expand...

That would be the Cadillac fix alright, but to be truly effective, you would want to rivet that aluminum strap into place. And then you would still have to add washers to prevent the steel bushings from ever digging into the softer aluminium doubler strap. To help disperse the loads much better than a regular washers, today I elected to file and bevel part of the edge of #3 (steel) area washers and nested the edges of those washers against the flanges. That should spread the load somewhat and effectively prevent any chance of the steel spacers EVER contributing to a local failure of the oil cooler flanges.

Rick Galati RV-6A "Darla"