This is a bolt on USFS approved spark arrestor for any 2 cylinder Mule. To build one like described here requires some advanced skills to bend and weld the exhaust pipes. The fully functional prototype was built using the tail piece and flange from an old muffler I had laying around and some 1 3/8" O.D. exhaust pipe. I am using the prototype to describe the project but for a production run, I would use 1 3/8" O.D. pipe, mandrel bend it and cut before welding to the mounting flange.
Probably the most common USFS Approved Spark Arrestor for this type of application is the SuperTrapp T-100 or T-101. The difference between the 2 is the T-100 is 3" in diameter and the T-101 is 5" in diameter. There is one paragraph in the documentation that is pertinent to the Mule.
The disks for each size is rated by the hp amount it should support. Each T-100 disk ( 3" ) is rated for ~3hp. Each T-101 disk ( 5" ) is rated for ~7hp. Using the information above we can calculate the number of disks required for each type. The Mule engine is rated at 14hp and we need to double that because it has a muffler. We need enough disks to support 28hp. The T-100 would require a minimum of 9 disks ( 28hp / 3 = 9.33 disks ). The T-101 would require 4 disks ( 28hp / 7 = 4 disks. ). For this project I am using the 5" T-101 Model.
The spark arrestor can be mounted so it sticks straight back by using straight pipe. My concern with that method is the way the back end of the 4 wheel steer Mule swings out. The arrestor could get caught on any tree or out cropping during a right hand turn. This would not only damage the arrestor but could also damage the muffler it is bolted to. I chose to bend the pipe to bring the arrestor back in behind the Mule to help prevent any damage.
| EMPI 3640 | This flange will have to be modified as the mounting bolt holes are not close enough together. The holes will have to be narrowed by 1/16" each side. Use a rat tail file or 1/4" drill bit to make the mounting holes closer together. The same applies to the gasket. You will also have to use washers on the mounting hardware as the holes are wider. | Reuse | You will need to cut the flange off the tail piece of the old muffler. ( See Figure C ). The flange is at the incorrect mounting angle. I used a grinder with a cutoff wheel. You will then need to remove the remaining pipe from inside the flange. |
| Note: | I don't care much for the gasket that comes with the EMPI 3640 kit. The gasket doesn't seal very well on the outside of the muffler flange. You can get exhaust gasket material from your local auto supplier ( or use an old header gasket ) and make one that fits much better. |
| Note: | If you reuse an old muffler pipe, you will have to add a 1 3/8" length of 1 3/8" OD pipe to mount the Spark Arrestor. If you cannot find a short piece of pipe, a suitable length can be cut from an exhaust adapter available at your local auto parts supplier. |
This list is dependant on the solution you choose ( Reuse old muffler tail piece or new using the EMPI 3640 kit and have a muffler shop do the pipe work ) and does not list common hand tools.
This list is dependant on the solution you choose ( Reuse old muffler tail piece or new using the EMPI 3640 kit and have a muffler shop do the pipe work )
Figure A: Pipe bend and dimensions. ( Click on image to enlarge. )
Figure B: Flange orientation. ( Click on image to enlarge. )
Figure C: Old Muffler tail piece reuse. ( Click on image to enlarge. )
Picture 1: Mounting adapter made from old muffler tail ( Click on image to enlarge. )
