Repairing/ Replacing broken studs on your fuel tank.

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Repairing/ Replacing broken studs on your fuel tank.

Postby HardwareBoB » Wed Jan 02, 2019 8:33 pm

It's a common issue for many subarus to snap studs on the fuel tank. Mine snapped one a while ago, but my fuel assembly has been in and out so many times, it eventually snapped two more, and leaked from the seal.

The original construction is a ring, which has studs pressed into it, and the ring is welded to the tank. It's unrealistic to service this, and if a Subaru dealer snaps your studs, they will fix it by replacing the fuel tank (which is a rear subframe out operation)

There's other ways of doing this, but this is the way I've done it, and it worked for me.

You will need:
8mm socket (no picture)
dremel with a cutoff wheel
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4.2mm drillbit (note it HAS to be a 4.2mm) (bunnings)
drill extension (normal drill head won't allow you to drill sttraight) - note you don't need the extra extension here, I bought it just in case. (bunnings)
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Stainless steel M5 x 25mm bolts - however many you need to replace (bunnings)
Fuel tank repair (super cheap auto)
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M5 tap and a tap driver.
A way to activate the fuel pump (mine is hardwired).
Jerry Can(s)
spare fuel hose.
2-3 microfibre towels you don't want anymore.

First, try to run down the fuel tank to nice and low, so there's not much fuel to drain.
Connect your fuel hose to the fuel line under the bonnet (the top hose) - this is easy for me because I had spare hose, and it's all AN fittings.
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Remove the fuel pump assembly. Fill the tank with water:
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Cut a cardboard/plastic/whatever plug to fit in and stop anything falling in while you're grinding.
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Using the cut off wheel, cut down the studs and try to get them smooth (which will make it easier to drill)
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Drill a centered 4.2mm hole - I used a microfibre towel I was holding under it and in the hole to prevent swarf going into the tank.
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Run the tap down the holes. same trick with the microfibre to catch the swarf.
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Grab your M5 stainless bolts, and run them up the holes - you might need a small spanner or a ratchet to get them started
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Make sure it fits (if it doesn't fit you might need to flare out the hole a bit)
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Now if you don't have a wet/dry vac, go and get the fuel pump assembly, place it back in (don't need to do anything up), re-attach the hoses, and run it until all the water is out.
If you have a wet/dry vac, Suck up all the water you can (ideally from just above the surface, so you can suck in anything that is on the top from surface tension)
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Attach the vacuum to the left most hose, which will suction the water from the other side.
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It might take a few minutes.
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Grab a clean microfibre and wipe down the inside of the fuel tank to catch anything you may have missed.

Back off the bolts a bit, put a bit of red loctite on them, and send them home.
Once they are on, make up some putty, and put it over the top of them. This may not be required with the tapping, but it doesn't hurt. Leave it for a few hours. If you're pressed for time you may want to leave this step out.
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Reinstall the pump Assembly (The extra lugs you can see there are the power to my fuel pump)
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Plug it back in and away you go!
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Re: Repairing/ Replacing broken studs on your fuel tank.

Postby craig_ » Wed Jan 02, 2019 8:48 pm

Nice work. Nice write up. Did you replace them all out just the ones snapped?

What's the torque settings on those studs?
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Re: Repairing/ Replacing broken studs on your fuel tank.

Postby HardwareBoB » Thu Jan 03, 2019 6:47 am

craig_ wrote:Nice work. Nice write up. Did you replace them all out just the ones snapped?

What's the torque settings on those studs?

Just the onea that snapped.

The torque settings is single digit - but the reality is that sometimes you need more to seal it.
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Re: Repairing/ Replacing broken studs on your fuel tank.

Postby BillyCorgi » Thu Jan 03, 2019 9:10 am

All that and you did not take a picture of the 8mm socket?
Such a breach of integrity!
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Re: Repairing/ Replacing broken studs on your fuel tank.

Postby bigBADbenny » Thu Jan 03, 2019 1:09 pm

So would filling up with eg e85 absorb any leftover water in the tank/s and lines?
Or do you just purge fresh fuel into a spare container before reinstalling the fuel lines?
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