German 36HP Dog House Fan Shroud

I've spent the past couple months getting ready for my new 2110cc motor that is being built.  I have collected all the engine tin, most of the ignition components and a good portion of the odds and ends. Today I thought I would post a write up on how I built my 36HP dog house shroud out of 2 German shrouds.  Let me start by saying, I'm not a mechanical engineer.  This is simply how I decided to work the cooling on my car.  If you decide to do this and you blow your motor up, or worse yet, hurt yourself in the process, don't come crying to me!

To start with, you will need a 36HP fan shroud, a dog house fan shroud, a spot weld cutter, die grinder with several cut-off wheels, a welder of some kind and an alternator/generator with backing plates and a a dog house fan attached. 

To start with, drill out the spot welds along the back of the dog house shroud that hold the heater tube veins in place.  There are 3 or 4 along each side but you will likely only be able to get to a couple on the passenger side (the left as you are working on the back side of the shroud).  You want these veins to come out with the front of the shroud so you don't care if you have to destroy them or not.

Now, flip the shroud over and drill out all the spot welds you can find on the front.  You can see there are 8 or 9 that form an arc around the fan.  These all hold the veins to the front of the shroud.  These are the veins we want to keep, so make sure you don't ruin them.  There are also 2 along the bottom under the shroud.  Again, don't ruin that piece.  We will be using a couple small pieces from the front of this shroud in later steps, so don't get rid of them just yet.

Now you can pull the front of the shroud off.  You will need to cut around the pinch seal that holds the front and back together.  I used my die grinder, but an air hammer would have done the job as well.  There will likely be a couple spot welds you missed that will have to be cut off as the shroud comes apart.  this picture shows a vein along the top of shroud.  This needs to be cut off as well, so now is a good time to dot it.

Now that we have the back off the dog house shroud, we need to cut the back off the 36HP shroud.  This time, it's the back we don't care about, so destroy it and the veins all you need in getting it apart.  You can see the spot welds I drilled in this one.  One word of warning though.  There is one vein above the fan we do want to keep!  Cut the back off leaving about half an inch of material so we have something to rest the new back on when we weld it together.

When you get the back off, this is what you should have.  The 2 veins beside the fan need to come off, so cut them off now.  Just be careful not to damage the front of the shroud.  The vein at the top will need some trimming to clear the inside of the dog house shroud back, but we will take care of that in a later step. 

Next up, you need to replace the center of the shroud with a small piece you cut off the dog house front.  This is for the case stud that the shroud sits on when the engine is assembled.  The 36HP case did not have a stud right below the shroud so we need to make sure our shroud clears this stud on the later model case.  I used an alternator backing plate to make sure the holes all lined up when I welded the new patch in place.

Now we need to clearance the top vein that is still attached to the front of the 36HP shroud.  You can see here where it hits the inlet for the air that is headed to the oil cooler.  You will need to cut the welding flange as well as the vein itself a little.  Cut only what you have to in order for the back to fit.  If you cut too much, you will allow air to escape into the cavity that is formed causing turbulence and reducing the air flow.

Here you can see the trimming I did.  I likely cut too much off, so I will spend some time later, patching the hole when the shroud gets welded back together.  Now is a really good time to sand blast everything and do any additional metal work you may need to do.  As you can see, I had a few holes to fill.  Since I will not have a coil, I started by filling those holes.  I also filled in the throttle tube holes so I can drill it in the correct location later.

Finally, bolt your generator/alternator to the front and set the back on.  Scribe a line in the dog house back around the outside edge of the 36HP shroud where it over laps.  Cut about an 1/8" inside that line so the new back will fit inside the lip like this.  Drill holes about 2 inches apart all the way around the new back, flip it over and drill new holes so you can spot weld the veins to the front as well and spot weld the hole thing together.  You can use the old dog house front as a pattern for drilling your spot weld holes.  I am also planning on drilling the holes so I can run the flaps inside this shroud as well.  Again, you can use the old dog house front as a pattern to drill the required holes for the flaps.  Like I said earlier, don't throw any of the metal away until you are finished because you can use the bits and pieces as patterns.