Started as a small ding in the corner (right footrest just behind where a passenger's foot would rest) (bought it that way-used). I've had a couple of good years riding this machine now, but watched this crack begin to grow last year, and it's now cracking up and out, probably an inch or more in each direction. It's also beginning to wrinkle the tunnel around the area. I was thinking....y'know rear suspension is supported by those 4 bolts to the tunnel, and I s'pose there's lots of force acting on that metal between those bolts. I probably need to get those wrinkles out and keep that metal straight.

I'm thinking of the following repairs:
-straighten the wrinkles out (hammer)
-weld the crack
-fabricate a plate to strengthen the area and install with several rivets

There isn't much clearance between the track sides of the tunnel, so I'm thinking there's no room for more metal on the inside. I'll have to add metal to the outside. I wonder if welding the tunnel can cause problems (making it more brittle? and prone to further cracking?). Anyone perform these repairs before? I'm looking for ideas / suggestions / advise.


Kind of late for no snow this year in Interior AK.

I'm pretty confident the weld will fail fairly quickly , and from the looks of the photo , it appears that you need reinforcement in 2 directions , horizontal and vertical . I would try a heavy gauge sheet metal "angle iron" , something near the thickness of the tunnel or slightly thicker , riveted from the inside . . . or even drilled out every 6" so that you could "plug weld" it on the outside of the tunnel and running board . The wider and longer that you make you angle iron repair , the better the chance that you can preserve your tunnel !

I'll agree with Tom here. Your reinforcement plate need not be too thick, your rear suspension - rear torque-arm drop brackets are a good example of thie thickness you need, those extend right up in there and do not hit the track. If your crack were further forward, I would suggest getting yourself a set of external tunnel braces as you see on some of the ditch-banging sleds (Polaris makes a good one for the Edge chassis series) but where it is so far rearward, you should fab up a set, bend them to be close to the radius on the tunnel/runningboard transition, then use button head bolts to bolt outwards through the tunnel. Riveting out through will give you the round head you want on the inside, but those rivet snouts are awfully ugly on the outside of your tunnel, they can catch on your clothes/boots as well and that's a real pain. I have found that short button head bolts (1/4" UNC or M6) and nylon locknuts are more aesthetically pleasing.

thanks
I think the plug weld idea, if done well, has potential to look/function the best. However, I'm also thinking maybe the least welding possible for now might be the best approach for me. Maybe just stitch the crack in a few spots to keep it from cracking further, and then attaching an angle plate for reinforcement.

If the angle plate is on the outside, that radius will be key, and I might take the material to a fab shop that can bend it with the correct radius

I recall the rear torque-arm drop brackets are pretty thick! I'll look at them tonight.

I have seen some factory accessory footrest supports - typically aluminum stuff and riveted on. That's the basic idea I guess.

I'll start looking for some material to fab an angle plate support piece.

here's a pic from the underside

Agreed. If you can do it right and clean it up properly, a plug weld will work excellent in this application; no bolt or rivet heads to get in the way.

Sounds like you have the problem in-hand, regardless what you choose to do, just make sure that it's fixed before you ride it this season or it will open up like you took a sawzall to the tunnel in no time.

The tunnel metal is around 0.075" thick (sorry, I don't have a metric caliper), and the rear torque arm drop brackets are double thickness of that metal welded together. I found a piece of sheet steel that measures right around 0.100" thick. The corner at the footrest is quite sharp, and so I think I can bend the sheet right at 90 with no radius, and it should sit in there well. I marked out a piece that will be 6" long coming out to the edge of the foot rest and up to the top of the tunnel (bottom of seat). Now to decide if I should do the welding, or rivets, or bolts...... Those rivet snouts might give my foot better traction....

As far as welding goes, I'll unplug the electrical box, disconnect the battery......anything I miss?

Uh-oh...
The footrest area has cracked away from the tubular framework. More welding....and a little more difficult to get at. How common is it for this to come apart?

Yes, that's a fairly common problem with the utility series sleds; the Skandic 440LT's and Tundra II's also had footrests that broke away from the side of the tunnel after some hard miles. When you think about it, we do demand a lot from these thin sections as our body mass is concentrated over our two - relatively - small feet right at the footrests when standing. You can see the runningboards flex a fair amount just about any time that you stand, even when new.

I would suggest not only running a good bead of weld around the steel chassis tube, but also installing a triangular corner gusset here and welding it in place. Do it on the other side as well before the problem presents itself.

When I am working on a project sled, often times I will inspect the welding where the footrest is attached to the side of the tunnel and re-weld it on in inch long beads, about an inch apart. This usually solves the problem.

Have a good look at the rear of the runningboards where the curled lip ends, my 2000 Skandic WT 500F developed a minor crack from that point after 10k or so km's which I was able to just weld and grind before it became serious.

I had a broken footrest on my shortie Tundra as well . I fabricated a small patch out of slightly heavier sheet metal that fit under the area that attached to the frame and predrilled for the rivet .

Click to view attachment

Riveted under the footrest and to the frame .

Click to view attachment

Results:
Straightened the metal. Welded the crack with patch metal behind it (tunnel metal is THIN!). There was adequate clearance between the tunnel and track for the metal patch. Using several rivets, I fastened the patch to the tunnel. With the patch behind, I can watch the area closely to see if problem is solved or persists. Not real purdy, but better than breaking down out in the bush.

I also repaired the failed welds at the footrest to tunnel. I added a triangles to each side to support this area better. Shouldn't fail ever again.

Great work. I will not add these photos to my "botched repair jobs" folder ...