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Check your flanges-Oil Cooler Flange Crack

Pmerems

Well Known Member
Advertiser
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.

Oil Cooler Flange Crack.jpg
 
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
 
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.
 
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/Projects/Oil_Cooler/Baffle_Aft_Rear.JPG
 
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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.
 
Rubber?

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/Projects/Oil_Cooler/Baffle_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?
 
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.)
 
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.
 
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.

Oil Cooler Flange Crack.jpg

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.
 
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.

Oil Cooler Flange Crack.jpg

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.
AUBobRdFmgN_ejJsc1sN2IqW_gmQbcHvw44abI2K1VvkAf33HdUZ7YA9LzYDbP92ZXs-bxAZCuncVsnVvhDy6BQPyu3Vxgz_UfQIM38t6n5LtZs3Gum3KViRKd11atetwq0hPpKeoFwx0239RO1J5j8ci62QO95q7DGboD54M5ZEtn3M1Flzp4Yi5VpXT0AKL-fe4DXhhwSd5OXiw41Rxyts9rUFiW4zoaLAKHYOZe39ArcehgGFZewLV9dgPAIuFy0y3nB8yhpg2Na1n3UWUL9qDFhEjxNhrXFHxHy9sjK6gPHfH0U7UtkXIZitZKsmw4wAP19BxbKPL21eWtwgl_8hZohYlWfvluXR-xoniTg89G9d9c1DTyDtDTABo33l-qNYjcSRm9f93bnlvZjQEjVpkgVYjGVevdIMyPjYvy6ZrD76cC7yKXkidqufvmj0pdXS2YLoUmNWl2QCs0dFmsDXAo9IyS_zsigCYsmp2JSOqmfCq18xjar7iK2NV2cJ3QjEodEYcfhRpA2yg-iTQYeb9VgBCuL5pE3vY-wkx9WYhD5FKPoeVuRdKcNI62mozN4SoFWG-2lg-2VWNIvs9xA7W9bBq0FLV5iy9BbfJoNTdOznCAwLbdrLX8shXGwrIugn5bXVrZ6XKrD2q6TZoO6CqVr4H-Fr=s370-no
 
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.
AUBobRdFmgN_ejJsc1sN2IqW_gmQbcHvw44abI2K1VvkAf33HdUZ7YA9LzYDbP92ZXs-bxAZCuncVsnVvhDy6BQPyu3Vxgz_UfQIM38t6n5LtZs3Gum3KViRKd11atetwq0hPpKeoFwx0239RO1J5j8ci62QO95q7DGboD54M5ZEtn3M1Flzp4Yi5VpXT0AKL-fe4DXhhwSd5OXiw41Rxyts9rUFiW4zoaLAKHYOZe39ArcehgGFZewLV9dgPAIuFy0y3nB8yhpg2Na1n3UWUL9qDFhEjxNhrXFHxHy9sjK6gPHfH0U7UtkXIZitZKsmw4wAP19BxbKPL21eWtwgl_8hZohYlWfvluXR-xoniTg89G9d9c1DTyDtDTABo33l-qNYjcSRm9f93bnlvZjQEjVpkgVYjGVevdIMyPjYvy6ZrD76cC7yKXkidqufvmj0pdXS2YLoUmNWl2QCs0dFmsDXAo9IyS_zsigCYsmp2JSOqmfCq18xjar7iK2NV2cJ3QjEodEYcfhRpA2yg-iTQYeb9VgBCuL5pE3vY-wkx9WYhD5FKPoeVuRdKcNI62mozN4SoFWG-2lg-2VWNIvs9xA7W9bBq0FLV5iy9BbfJoNTdOznCAwLbdrLX8shXGwrIugn5bXVrZ6XKrD2q6TZoO6CqVr4H-Fr=s370-no

Bill, there are a couple of problems with the solution you show. It's simple but in reality it is too simple.

Firstly the brace applies an eccentric load on the oil cooler bolt which in effect wants to bend the bolt (and bend the cooler flange) thus leading to flexing and potentially fatigue cracking of the flange.

Secondly the brace is only picking up one oil cooler bolt so the eccentric loads are concentrated.

The solution is to design a bracket that picks up two of the cooler bolts, and to design it so that the axial forces in the brace are being picked up on a line that runs directly between the centreline of the two bolts (and preferably midway between the bolts). That will give you a concentric loading (all loads going to a common centre) and will reduce the tendency for bending. The brace can then be fastened by a third single bolt to the bracket.

And finally the 2 cooler bolts that pick up the bracket need to be long bolts that pass through both flanges of the oil cooler (obviously with a compression spacer in between) so that the front flange is not accepting all of the loads.
 
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Bill, there are a couple of problems with the solution you show. It's simple but in reality it is too simple.

Firstly the brace applies an eccentric load on the oil cooler bolt which in effect wants to bend the bolt (and bend the cooler flange) thus leading to flexing and potentially fatigue cracking of the flange.

Secondly the brace is only picking up one oil cooler bolt so the eccentric loads are concentrated.

The solution is to design a bracket that picks up two of the cooler bolts, and to design it so that the axial forces in the brace are being picked up on a line that runs directly between the centreline of the two bolts (and preferably midway between the bolts). That will give you a concentric loading (all loads going to a common centre) and will reduce the tendency for bending. The brace can then be fastened by a third single bolt to the bracket.

And finally the 2 cooler bolts that pick up the bracket need to be long bolts that pass through both flanges of the oil cooler (obviously with a compression spacer in between) so that the front flange is not accepting all of the loads.
Too simple, maybe, I am guilty on occasion, we are going to see. It is a full length bolt, BTW. I mounted to the center of the cooler as it is closer to the mass center and less likely twist the cooler as it tries to pivot about the outboard edge.

Other designs (serving the same function as this rod) that stiffen that end of the cooler have given good service to TBO, but this design (admittedly) is different, what is your projection for fatigue life?
 
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Well known issue. I used 3/4 x 3/4 x 1/8 inch angle the full length of the flange as the "clamping strip". A little extreme as large area washers seem to work for many.
I also cut the spacers short enough to put a washer between the ends of the spacers and the flange. Basically, made a sandwich so the load is carried by the bolt, spacers, angle, and washers and distributed across the full length of the flange.
 
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Too simple, maybe, I am guilty on occasion, we are going to see. It is a full length bolt, BTW. I mounted to the center of the cooler as it is closer to the mass center and less likely twist the cooler as it tries to pivot about the outboard edge.

Other designs (serving the same function as this rod) that stiffen that end of the cooler have given good service to TBO, but this design (admittedly) is different, what is your projection for fatigue life?

Bill, my best guess is that the OP developed a crack in his cooler flange because he did something very similar to your proposal. But he didn't say how many hours its took to crack. I think the brace is a good idea but once you instal a brace all loads will run through it so it needs a bit of thinking put into it.

I would definitely pick up the two available bolts, not just the one. Make a vertical bracket out of angle or T section that picks up both bolts and bolt your brace to that bracket. I doubt you'll ever have a problem in the future if you do that.

When the oil cooler is full of oil it has quite a lot of mass and concentrating all of the resultant loads at one location on the cooler flange is just asking for a problem, particularly with an eccentric connection.
 
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.
Bill,

That is similar to how I did my first engine install and it held up well.

When I replaced the engine in my plane, the baffle cracked, not the oil cooler, right along the rivet line between the side and back baffle on #4.

After replacing the baffles, I nested a thick piece of AA on the outside. ~500+ hours and no cracks. (I also lengthened the AA so I could hang the plug wires off of it.)

Note the washers on the aluminum tubing spacers. They are on both ends of the tubing and help spread the loads on the cooler flanges. 500+ hours and no cracks on the flanges.

2012-01-27_21-53-53_700.jpg
 
Righto.
To followup on my original post that reignited this thread, I've finished my oil cooler inboard reinforcement and the pictures may be found below. As per most setups, on the inboard side the top bolt will be a through bolt and tube as intended by the cooler manufacturer. The middle bolt will be a short bolt, due to the conflict with the engine mount tube at the rear hole (see the clearance cutout in the pictures). There will be no lower bolt, due to the conflict with the oil cooler fins on the forward side.
The brace consists of a lengths of 1/16x3/4x3/4 6061T6 riveted to a top plate of some 0.050" alclad with 3/8" flanges bent up on the sides. The assembly is painted with high temperature enamel and riveted to the oil cooler with CS4-4 on the forward face and LP4-3 on the rear.
I can't say it's any better or worse than other solutions, however I though this may help better distribute the loads across the flanges and stop the bending loads on the forward flange that occur with the brace across to the top of the #4 cylinder in place. Ultimately though, if I was to do this I might incorporate a 1/8" angle on the front flange, as this design of mine still transmit bending loads through the corner of the angle. I also think that 50 thou for the top plate was overkill, but I didn't have any 0.040" on hand, and 0.032" felt too light.
I might make these modifications when I build the next aircraft... then again, it will be electric so an oil cooler won't be on the cards.
Tom.
2m3gw8h.jpg


2n0japu.jpg
 
Bill,

That is similar to how I did my first engine install and it held up well.

When I replaced the engine in my plane, the baffle cracked, not the oil cooler, right along the rivet line between the side and back baffle on #4.

After replacing the baffles, I nested a thick piece of AA on the outside. ~500+ hours and no cracks. (I also lengthened the AA so I could hang the plug wires off of it.)

Note the washers on the aluminum tubing spacers. They are on both ends of the tubing and help spread the loads on the cooler flanges. 500+ hours and no cracks on the flanges.
Thanks, Bill, I did a lot of research before settling on this one. The far left vertical and tie over the the top crew on the head is added too, ha - I extended the AA for wires too! In order to sort of balance the wagging mass close to the center, the middle bolt was desirable, and that head location was the only available anchor. Many attach to the case and the top cooler bolt and have successful results if it is stiff. A case anchor might have been best but the geometry does not allow that to the center bolt.
Edit: Oh and also have washers for the long spacer, terrible contact without them.
A picture - in process with temp screws.
XJQgmQlvJa1iVYPAAqttnaUH91zx7660IT6PBhNzKy9qGKjNlkdJhfZkeEVky03wK7_qzsZhQP3gDZO2qt9zmFz8c0p-xT1L1w-rieukhR3ziGgwRvT6L_ysrTOLo8IZ9rotIfYbPfGXNLs7e0r_Mbiowr2ZzFJy0xDsgL_3bejM8tqaRZPbeQKA50CFJltZTiF-_FowS02mYie1o5tqG147NiPIx_p_HcH8hV5CVv1IAbuPTwC_yDwXOgghCmxVpCHkQO8SWWQWl3-U8d4hQzsWuV1_uhKEIyE9uQ23Qx7l_yL-k1bp68bhJepEK3ut-x-Be0NWN-16WGVOrIrrY_swXsMep0tazGwTYafryy8znbMfSI87qjJi-CEj3XxFsbWGNr40ty61y2jX-waIErgaxrCThgfPPHVumskrsbc37SErXhVI1LhZZAJvIrjEOywHo8TEmhMFo0OrZ-YHuj7X0gaeHDLoa7cjP9e5_56kIEI_LNCw6U7CCOgq7jGv-RmLEOOuNLdJx_9bJ4eZbqidJpK7zzYb1mutQA47TsyZKTE95-eaFgu1i-B3oZ1XSbI-KCcvzARXF8gfPRk_X5De2RDUm8kg3c29QVeR3wPnJ99deI9qHh4U6eTpKqX3jv6anW987xtE9xnZBfMEIF6hbwYC87jA=w700-no
 
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Righto.
To followup on my original post that reignited this thread . . . . .

Tom, nice work, could you repost your original picture of the installation? It would help greatly in the understanding of what happened here.

Thanks
 
Hi Bill,
I've never flown my aircraft, so this could be considered a pre-emptive strike. I just looked at the original configuration intended for use by Van's that lacked the through-bolts and tubes on the lower two inboard mounting positions and thought something needed to be done about this. I then saw the post from the OP of this thread and it confirmed my theory that this oil cooler flange was a potential failure point in addition to the usual cracking of the baffles at the corner of #4 cylinder, so I got at it and developed this solution. This will be combined with the CRMO tube brace from the midpoint of this inboard flange back to the top of the #4 cylinder and the corner reinforcement you point out in your previous post.
Cheers,
Tom.
 
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