Cracked rear tunnel

snobyrd · Dec 4, 2017

Iv got a 163 thats got a crack in the rear of the tunnel where theres a factory drilled hole in the rolled edge at the end of the inside bracing. Its being brought to a local welding shop to be welded, sled is still under warranty but not putting any faith into polaris to repair it.
Im looking for info on a good bracing kit that i could put on the side ,perhaps with the rolled lower edge to reenforce the tunnel and cover up the repair after welding.

Murph · Dec 4, 2017

Any pictures of it?

Might go with a BM Fab rear bumper- they extend down to rolled edge and all the way forward to running board support.

The welder needs to be really careful with the amount of heat used-- you don't want to weaken the tunnel around the weld.

gtwitch · Dec 4, 2017

I like the Mountain Armour rear bumper (made here in Wyoming) and have it on 4 sleds now and really does good job of tunnel braceing!
gtwitch in wyoming

Rick! · Dec 4, 2017

How big a tunnel bag is on it, how many lbs of stuff is in it, and how far behind the seat brace/rear suspension mounting bolt is it?

Pix will tell a story for sure.

snobyrd · Dec 4, 2017

Rick! said:
How big a tunnel bag is on it, how many lbs of stuff is in it, and how far behind the seat brace/rear suspension mounting bolt is it?

Pix will tell a story for sure.

no storage bag or jerry can. The crack started in the rivet hole on the curl where the last inside brace stops.

Mr. Pump Gas · Dec 4, 2017

VanAmburg will make a full length custom tunnel brace/bumper combo. Nice piece and very solid.

LoudHandle · Dec 5, 2017

Murph said:
Any pictures of it?

.....

The welder needs to be really careful with the amount of heat used-- you don't want to weaken the tunnel around the weld.

Polaris and most manufactures use 5052 aluminum for the formed portions of the tunnel which is not a heat treated nor a heat treatable alloy. Welding will not effect it's strength (positively or negatively).

Depending on what direction and how far the crack has propagated, I'd consider stop drilling it and calling it good. As running a weld over the top of the crack will do nothing beneficial other than lighten your wallet and give you a false sense of security. If the crack is not stop drilled and 100 percent fused back together, it has a good chance of coming back.

Murph · Dec 5, 2017

LoudHandle said:
Polaris and most manufactures use 5052 aluminum for the formed portions of the tunnel which is not a heat treated nor a heat treatable alloy. Welding will not effect it's strength (positively or negatively).

Depending on what direction and how far the crack has propagated, I'd consider stop drilling it and calling it good. As running a weld over the top of the crack will do nothing beneficial other than lighten your wallet and give you a false sense of security. If the crack is not stop drilled and 100 percent fused back together, it has a good chance of coming back.

Awesome--thanks for the info!

snobyrd · Dec 5, 2017

The crack is being welded today, its mostly for lipstick, we're putting a vanamburg product on it to cover up the repair and strengthened up the sides. We get stuck alot and i guess the constant lifting on the bumper has taken its toll. Moving foward, we need to buy rear tunnel stiffeners to avoid this issue.

Rick! · Dec 5, 2017

LoudHandle said:
Polaris and most manufactures use 5052 aluminum for the formed portions of the tunnel which is not a heat treated nor a heat treatable alloy. Welding will not effect it's strength (positively or negatively).

Depending on what direction and how far the crack has propagated, I'd consider stop drilling it and calling it good. As running a weld over the top of the crack will do nothing beneficial other than lighten your wallet and give you a false sense of security. If the crack is not stop drilled and 100 percent fused back together, it has a good chance of coming back.

All good info except the bolded statement.

How does strain hardened aluminum not get its base strength reduced due to welding? Weldability shouldn't be confused with post weld strength.

jim · Dec 5, 2017

5 series aluminum is not heat treatable but does readily strain harden. So, anything done to roll or form it will give it its strength via strain hardening. Welding will produce a heat affected zone that will allow the molecules to go back to a relaxed state (eliminating any strain hardened metal) and will create a weak zone around the weld.

Best way to stop an aluminum crack is to drill a hole at the tip of the crack and then rivet.

IMO, the ideal way to fix a crack in aluminum is to drill a hole at the tip of the crack and then reinforce the entire area surrounding the crack with some type of base plate material to reduce the stress at that region and stop the crack from growing.

LoudHandle · Dec 8, 2017

My Opinion; FWIW

Hardness should not be confused with Strength.

Just because your third leg gets hard to have sex, does not mean you are stronger while performing the act. Although some of you ego manics will take exception to that analogy.

The reality is they are for the most part exclusive properties in this case.

Additionally the hole is only there for the locating pin; used to position the tunnel side in the press break while the forming is done. A crack from this location would be a result of incorrect pin to hole spacing / alignment resulting is excessive forces (too much strain hardening) applied during the forming. So relieving the stresses and allowing it to return to a more normalized state will be beneficial. IMO

Personally I replace the tunnel sides with better material as the 5052 is essentially a low cost, low strength (garbage) alloy to start with. IMO

tuneman · Dec 8, 2017

5052 is far from a garbage alloy. It's an aluminum with very good strength that you can actually form without cracking.

LoudHandle · Dec 8, 2017

tuneman said:
5052 is far from a garbage alloy. It's an aluminum with very good strength that you can actually form without cracking.

I work with it every day, being a fabricator by trade. 5052 has it's place, I just disagree with it use for tunnels and such. There are far better materials available for use as stressed members.

Additionally nearly all aluminum alloys can be formed if you adhere to the published die radius to metal thickness ratio for that alloy. 5052 is just the cheapest option and more forgiving of cheating the published ratio. As a rule it is 25% weaker and 25% cheaper than the next better choice so it gets used more often and in places where it really should be one of the stronger alloys.

snobyrd · Dec 12, 2017

Heres some picts of the crack

Snowbird11 · Dec 12, 2017

snobyrd said:
Heres some picts of the crack

wow, what's your best guess at the cause? i think you're right to try and brace it with a bumper kit. if it were on polaris's dime i'd want a new tunnel.

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Cracked rear tunnel

snobyrd

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Murph

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gtwitch

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Rick!

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snobyrd

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Mr. Pump Gas

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LoudHandle

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Murph

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snobyrd

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Rick!

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jim

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LoudHandle

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tuneman

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