Chimaera Fuel Sender mounting hole is stripped

[NJ94Chim]

Just figured out why I smell gas every time I fill up: the fuel sending assy is secured to the top of the fuel tank by five M5 hex bolts. One of them is stripped, allowing a little bit of fuel to splash around and come out when the tank is chock full.

I've tried wrapping pipe fitters tape around an M5 bolt - hole is too stripped for that. Can't use an M6 as it wont fit thru the fuel sender assy hole.

And there aren't any SAE sizes that are a bit bigger than the M5 that I could self-tap into the hole.

So it looks like I have to use a helicoil insert. Just ordered a metric multi size kit.

But I have never done a helicoil before, and am leery of the first time being on the aluminum flange that accepts the M5 bolts.

I know I will need to be careful to not drill down thru the bottom of the aluminum flange. (Bolt holes do not penetrate into the gas tank volume)

Any suggestions on how I might avoid having to go with the helicoil?

Or for that matter, any suggestions on what to be on the lookout if I do have to use a helicoil?

Thanks

[Belle427]

Cant you just drill out the fuel sender flange hole to 6 mm?
If not you probably want to use a rivnut or threaded insert as they are called, the kits can be expensive with the tool but there isnt anything that special about them so a cheaper one would do.

[PabloGee]

Is the thread fully stripped?

I've had a couple of bolts (not in the same spot) where the bolt was fairly stripped, but the threaded hole was in better condition.
It needed a tap tool to re-run the thread (make sure it's the correct one - I discovered the previous owner had used the wrong bolts with the wrong thread pitch), then a new bolt and a bit of thread locker to hold and seal it?

It's not a structural part of the car, so it just needs a proper seal, no?

I'm not the expert though...

[Sardonicus]

Stud and nut the hole (blind IIRC) or tap deeper or just take out to M6 its really not an issue

[NJ94Chim]

Thanks for the suggestions.....

Looks like the tap for the M5 helicoil is 5.2mm OD, so it should be doable to tap it by hand. I am thinking that, even if the stripped out hole is sloppy around the helicoil insert after using the tap, a bit of permatex should tighten it up enough.

Helicoil kit comes today...what would we do without Amazon.

Will post back with results

Thanks again.

[NJ94Chim]

Well, helicoil insert worked, fuel level sender is now snug. One of the other five bolts tried to strip out its hole. Hard steel in short aluminum hole is not a good match.

But now on to the next thing.

Thanks for everyone's suggestions and help

[PabloGee]

Well done.
Might be worth checking the filter on the inside of the tank for drilling debris, it’s hard to catch it all of course, and doesn’t the end of a helix oil get knocked out?

[NJ94Chim]

The bolt holes are only about 3/8" deep and don't penetrate down into the interior tank volume. It looks like the bolt holes are drillled all the way through the mounting flange, but after it gets spot welded to the top of the tank, they coated the interior around the flange with some kind of continuous plasticy-rubbery stuff. Smooth to the touch, completely covers the transition where the flange is attached. In any case did not want to drill through that.

The right answer for this, now that I think about it, would be to insert M5 studs in each hole, permatex them into the mounting holes, and then secure the fuel sender to the studs with nuts. If I can find 20mm and 25mm M5 studs, I might go ahead and do this. Would have the added benefit of allowing you to seat the gasket first and then drop the sender down onto the studs.

Uh, "filter on the inside of the tank"? Drawing a blank on that: where would it be located/accessed?

Maybe there's an in-line filter somewhere after the tank?

[PabloGee]

Good stuff!

Filter - at the exit point of the tank at the bottom, if you were to have a drained tank, then undo the large hose tail from the tank, you find a filter fitted the the back of it.
All this I believe can be done from the rear wheel arch, but I've only read about it on the Bertram Hill website
https://www.bertram-hill.com/replacing-the-fuel-li...

But thankfully you don't seem to be in that situation...