The bumper for the 1M is made of a plastic that's nice to grab onto. Unfortunately it has a tendency to crack and break around the mounting holes that hold onto to the aluminum extension. It appears the stress is a combination of vibration and lifting the sled out of a trench. In my case the right rear hole broke. I had a warranty exchange and decided to beef the mounting to help prevent this from happening again. So with a high effort on stress relief for the plastic I improved the surface mounting area.
Here, with the new replacement bumper, I'm pointing to the hole that likes to break. I also noticed another minor problem. With the flap off I notice it, too, was starting to break a little as you can see the first crack on the right picture. This might be from bending back while riding in deep powder, or while sitting in a trench (stuck). I was told the flap is not warranty (normal wear). So, (making note of that small limitation) I went to work to improve the mounting of the flap as well.
First, I marked and drilled one extra hole on each side to help with the stress point of the bumper bolts. Here's the three holes on the one side. Notice the stock holes are quite a bit larger than the 1/4" bolt they use. Looks like some slop, so I went with just a 1/4" hole so the third bolt will be snug. The OEM bolts are a torx 27 with a clip type nut, which don't give any flat support to the plastic (weak points) areas. Also there's another issue; the most rear bolts are into the heat exchanger area and really hard to access the heads to loosen. For those reasons I dumped the clip type and went with conventional nuts, with the nylon locking inserts. Side note;as you can see I haven't addressed the hose clamp issue, yet.
In this view you can see the plastic mounting area is offset to allow room for the OEM clip type nuts. I see this as a weak point in design, since the stressed area does not make direct contact with the tunnel extension, rather depends on the sheer surface of the plastic hole riding on the bolt. And there's not a lot of thickness of plastic to the edge, so yes, the bolt "cuts" it's way to the edge and breaks out. I wanted to improve the two surface's contact area for less stress on the plastic in one (small) area. Therefore, I installed a 7/8" OD washer, with a 1/4" I.D., on each stock hole area. They don't quite fit (a little too snug), so I heated each washer just enough to slightly melt into the edges of the indentation of the offset hole edges, being careful not to melt into the holding surfaces of the plastic. Another way would to ream the edges out with a knife or dremmel tool. I used conventional 1/4" nuts, with the locking nylon insert in them. Because of the extra thickness of these locking nuts I went with 1 1/4" bolt length, instead of the OEM 1". Also added a bead of RTV silicone glue between the two surfaces for improved surface (friction) holding. With using the nuts you can use a open end 7/16" wrench to easily tighten them, including the most rear one that is too tight of to get your driver which hits the heat exchanger. (see the previous picture).
The stock flap is mounted with three bolts to the bumper. By now, the center was broken off. So I decided to add four more bolts, evenly spaced so it looks good. The OEM parts were not available with the $100 minimum order to Cat, so I temporarily used hardware from the local store. I found similar hardware, which was 1/4" course thread 1/2" long, bolts with a large "pan" head and locking nuts with the nylon inserts, with appropriate flat washers. Where the hole ended up was near some of the plastic cross brace, so I cut the area(s) out with a knife for the washers to sit.
Here's an inside view of most of them installed (one left to do) including the original ones on the outsides. The center "hole" is where the original center one was, now is gone from cracking. I did continue to use two of the OEM clip type nuts, since they don't have a high stress pull on them. These are the two for the front ends. Most of the force is pushing down on the rail in these areas. The other reason is there is no room to turn any nut, since they are in hidden areas. (right picture).
With the washers fitted into the plastic area of the bumper and the flap mounted I was ready to re install the assembly with the glue. As I tighten the bolts down it squashed the excess glue out; just cleaned it up with a rag. Here's the inside view, with all the new bolts tightened into the tunnel extension. The right picture shows the flaps and new bolts. When the OEM bolts come in next fall I'll change them out so they are all the same color. There's just enough room to slip some needle nose up inside the flap, so you don't have to break the glue. The final product came out nice, sitting on my latest summer rack on rollers.
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