Check your flanges-Oil Cooler Flange Crack

Pmerems · #1 11-21-2012, 08:20 AM

Gents,

During my 140 hour conditional inspection I discovered cracking of the oil cooler flange (inboard side). I have a reinforced rear baffle and a diagonal cross brace from the #4 cylinder head to the forward side of the rear baffle where the oil cooler is mounted. The cross brace attaches to the bolt location where the cracking is occurring. The cooler is a SW 8406R. It appears that by making the baffle more ridged it is transmitting more stress to the cooler flange.

According to Pacific Oil Cooler service, cracked flanges are very typical for baffle mounted oil coolers. A simple weld repair is in the future with a modification to the cross brace to reduce the rigidity.

Please check your oil cooler flanges for cracking.

tgmillso · #2 01-19-2018, 10:00 PM

Is this a common issue or a one off? I was working on positioning my cooler today and realize that the inboard side is poorly supported in that the middle bolt will not pass from the rear flange to the front flange as you need to notch the rear flange at this point to clear an engine mount tube. I am thinking that a piece of 063 3/4x3/4 angle riveted along the forward flange would help distribute the loads along the entire length of the cooler flange. In addition it would be possible to rivet this angle flange to a corresponding angle riveted along the rear cooler flange. This should distribute the loads to the rear flange the way the long bolt and tube assembly would if it was possible to install. I'll upload a pic to try and better explain this once I get home.
Tom.
RV-7
IO-360M1B

AX-O · #3 01-19-2018, 10:21 PM

I had a crack within Approx 100 hrs. They welded it and sent it back. I think the problem is that the flange gets bent 90 deg and it puts stresses on the metal because the small radius. My cracked right down that 90 deg bend. It also does not help that the 3 mounting holes are so close to the 90 deg bend.

az_gila · #4 01-20-2018, 02:19 AM

Quote:

Originally Posted by tgmillso

Is this a common issue or a one off? I was working on positioning my cooler today and realize that the inboard side is poorly supported in that the middle bolt will not pass from the rear flange to the front flange as you need to notch the rear flange at this point to clear an engine mount tube. I am thinking that a piece of 063 3/4x3/4 angle riveted along the forward flange would help distribute the loads along the entire length of the cooler flange. In addition it would be possible to rivet this angle flange to a corresponding angle riveted along the rear cooler flange. This should distribute the loads to the rear flange the way the long bolt and tube assembly would if it was possible to install. I'll upload a pic to try and better explain this once I get home.
Tom.
RV-7
IO-360M1B

In a similar vein, the baffle mounted cooler on my certified Tiger specifies a 'clamping strip' that fits over the oil cooler flange and spreads the point loads from the mounting bolts. IIRC the strip is about 1/8 inch thick.

It's a simple change to add a similar strip to both oil cooler flanges on any RV.

Added, picture stolen off the web showing the clamping strip -
http://www.aucountry.com/ACA_Folder/...e_Aft_Rear.JPG

tgmillso · #5 01-20-2018, 05:08 AM

Excellent. Thanks guys. After a bit more eyeball engineering I started work on it today but didn't get it finished. It's evolved a bit from my original description, but should do a good job of turning the bending loads on the forward flange into more of a shear load distributed between the forward and aft flanges the way the original through bolt design intended. I have to say that this far into the build (it's painted, final assembled, interior done etc. and only the avionics left to wire) I was hoping that these baffles would be a walk in the park, but frankly the whole baffle and snorkel experience has been almost as painful at sealing fuel tanks. Hopefully the avionics will be more enjoyable so I can end on a high note.
Tom.

PilotjohnS · #6 01-20-2018, 06:38 AM

Quote:

Originally Posted by az_gila

In a similar vein, the baffle mounted cooler on my certified Tiger specifies a 'clamping strip' that fits over the oil cooler flange and spreads the point loads from the mounting bolts. IIRC the strip is about 1/8 inch thick.

It's a simple change to add a similar strip to both oil cooler flanges on any RV.

Added, picture stolen off the web showing the clamping strip -
http://www.aucountry.com/ACA_Folder/...e_Aft_Rear.JPG

Gil
It looks like that clamping strip in the picture is rubber, and there is another rubber piece between the cooler and the baffle. Am I seeing this right?

N941WR · #7 01-20-2018, 07:45 AM

The instructions don't call for washers on each end of the aluminum spacers. If you install them so the burr is away from the flange, you will probably not have cracks. (800 hours and no cracks.)

az_gila · #8 01-20-2018, 09:40 AM

Quote:

Originally Posted by PilotjohnS

Gil
It looks like that clamping strip in the picture is rubber, and there is another rubber piece between the cooler and the baffle. Am I seeing this right?

No, but it was the best pic I could find...

There is a rubber gasket (baffle material) between the cooler and the baffle, but the strip under the base of the two spacer tubes is 1/8 aluminum. I think the AN970 washers under the bolt heads also help spread the loads on the aft cooler flange.
The inner flange of the cooler has short bolts directly on the forward flange, and they also have a 1/8 clamping strip IIRC.

Captain Avgas · #9 01-21-2018, 01:48 AM

Quote:

Originally Posted by Pmerems

Gents,

During my 140 hour conditional inspection I discovered cracking of the oil cooler flange (inboard side). I have a reinforced rear baffle and a diagonal cross brace from the #4 cylinder head to the forward side of the rear baffle where the oil cooler is mounted. The cross brace attaches to the bolt location where the cracking is occurring. The cooler is a SW 8406R. It appears that by making the baffle more ridged it is transmitting more stress to the cooler flange.

According to Pacific Oil Cooler service, cracked flanges are very typical for baffle mounted oil coolers. A simple weld repair is in the future with a modification to the cross brace to reduce the rigidity.

Please check your oil cooler flanges for cracking.

If you post a couple of pix of your original configuration (one from front of baffle showing engine brace to cooler connection and one from rear of baffle showing cooler flange attachment bolt) then we may be able to advise you why your system failed. My guess is that the fault lies not with the cooler but with your installation.

BillL · #10 01-21-2018, 05:07 AM

Quote:

Originally Posted by Pmerems

Gents,

During my 140 hour conditional inspection I discovered cracking of the oil cooler flange (inboard side). I have a reinforced rear baffle and a diagonal cross brace from the #4 cylinder head to the forward side of the rear baffle where the oil cooler is mounted. The cross brace attaches to the bolt location where the cracking is occurring. The cooler is a SW 8406R. It appears that by making the baffle more ridged it is transmitting more stress to the cooler flange.

According to Pacific Oil Cooler service, cracked flanges are very typical for baffle mounted oil coolers. A simple weld repair is in the future with a modification to the cross brace to reduce the rigidity.

Please check your oil cooler flanges for cracking.

I can not see your picture, is this how you attached your brace? Not flying yet, but the reservations of the design are the stiffness. It is a solid steel rod with hammered flats on the ends for attachment. Couldn't think of some elegant way to add an elastomer there. I am open to design suggestions.