Electrical Sender Grounding and Fuel Tank Sealing question

[DanH]

Originally Posted by RV6_flyer

The ground wire is on a lug like this one. Yes there is good electrical contact using an ohm meter.

Nicely done.

Note that Gary's solder lug installation is also environmentally stable. Long term, it is unlikely to add resistance due to any reasonable level of corrosion.

[precession]

Wow, what a great set of replies, even including beautiful pictures no less. My thanks to all who took the time to reply, this really helps. (Glad I sent Doug my yearly contrib too - paid off in one post.)

I was even wondering what type of lock washer, and Scott confirmed star-type - I guess because those little points will always poke through any sealant and contact the underside of the screw head above and plate below.

I wasn't aware that current plans call for "filing sanding a bevel on the edge of the sender flange." I assume that means filing a bevel on the underside outer edge of the sender plate (the side that contacts the access plate) so in the future you can insert a screw driver into the bevel to pry the sender plate off if necessary(?). I think I'll do that rather than place washers underneath the sender flange/plate.

The only part I'm still having a problem with is the idea of not fully tightening down the fastening screws on the both the access plate and sender plates. I'm hoping someone can maybe restate what the current instructions are for exactly how much you are supposed to tighten the fastening screws after you have put down your sealant - i.e., how much of a gap you are to leave between the two plates - because it is really going against my grain to not tighten down the plates flush and have nice, tight, and torqued screws. ??

Reasons for the question: When cork gaskets were used, you obviously had the cork that you would feel creating compression when you tightened your screws. You wouldn't fully tighten your screws (because you wouldn't want to overly compress the cork), but you would at least feel the cork creating some compression, and that compression, along with the sealant, presumably provided some force keeping the screws from vibrating loose. But now you are not using cork, only sealant, so it seems that if you don't tighten the screws to the point that the two plates are flush, there will really be nothing against which to create any compression on the screws - only the viscous sealant, which isn't going to provide any real resistance. So (1) I will be creating a gap between the plates that probably will not be of uniform thickness, because I'll just be eyeballing it, and (2) the only thing to prevent the UNtightened screws from vibrating loose will be the grip of the nut plates and the sealant that will harden around them?? Is that enough? And besides, don't you need some pressure on the screw or screws with the star washer under them to insure firm contact from the underside of the screw head to the washer to the plate below it?

Maybe my instincts are just wrong on this point, and I haven't seen the current instructions, so thanks in advance for any additional comment.

[Carl Froehlich]

I never heard of bevels or leaving screws loose.

I built a lot of tanks with no leaks with a straightforward approach:
- I use the cork gasket on the inspection plate. I add pro seal to the cork gasket on both sides, as well as the tank opening and plate. My thought was that if I ever had to disassemble a razor blade cutting the gasket would work. Never had to do this so I cannot comment on how well it would work.
- For the fuel sender I first used the rubber gasket, again with proseal on all mating surfaces. The screws tighten enough for the gasket to compress. Of late I?ve not used the rubber gasket (per the Van?s instructions). No leaks with either approach.

The only tank I?ve seen leak at the fuel sender is one the buildier made using only the rubber gasket - and it was leak free for 13 years. Pulled the sender, threw away the old gasket and put proseal on the mating surfaces - all is well.

Bottom line, this is fairly straight forward. Press on.

Carl

[az_gila]

I would take the "screws loose" comment as -

Do not torque down and just tighten the screws until you have a 'squish' of Proseal around the entire circumference of the sender/access plate.

Not quite the same as "loose", especially after the Proseal sets.

[rvbuilder2002]

Originally Posted by az_gila

I would take the "screws loose" comment as -

Do not torque down and just tighten the screws until you have a 'squish' of Proseal around the entire circumference of the sender/access plate.

Not quite the same as "loose", especially after the Proseal sets.

Exactly

Makes the cover or sender much easier to remove.

[precession]

Okay guys, thanks for the additional replies, they are much appreciated.

Based on them, I will go ahead and attach both the sender and access plate using just the tank sealant as my gasket (i.e., won't use the rubber on the sender plate, or cork on the access plate, even though I bought the cork and appreciate Carl's description of how to apply proseal when using cork).

I will tighten the screws until they are close to, but not totally, down and I get a hopefully roughly uniform amount of squished out sealant around the perimeter of the plates. I'll have one or more star washers on both plates to achieve the electrical connection.

Thanks again for the excellent help and alleviating my concerns. Really need to get this bird back in the air.

[rv7charlie]

For what it's worth, I've mentioned this product:
https://www.permatex.com/products/ga...lange-sealant/

in several prior threads on sealing the access cover and sender. I've had it in service on my -4 for a number of years, and never had a leak. I *have* had to re-open a tank to fix additional *proseal* leaks, and the really nice thing about this stuff is that it never hardens. Gentle pressure is all that's needed to separate the parts later (even years later). It's impervious to both av and mogas. My technique is to spread a thin layer on both surfaces, as directed, and then a small drop on each screw hole (enough to cover the hole) prior to inserting the screw. Tighten screws to normal torque; the sealant fills any microscopic voids but allows normal torquing of the screws. I haven't done it, but you should be able to use the star washer & eyelet for external ground wire, if desired.

Available at most auto supply stores.

Charlie

[swisseagle]

You will need a ground cable from the sender to the tank-structure.
Dont ask how I know ... It took a while to find this out. It was wheater related, high humidity it was ok, dry it was not grounded. If you where measuring ... then it was nealy ok ... I could only see, that I could not measure it twice the same Ohm value ... Then after a ground strap was added, no problem anymore.

[JonJay]

Originally Posted by JonJay

Scott plus Gary = 200% of people I trust.
I have an intermittent sender. I will clean up one of the screws, clean, reseal and add the star washer. I?ll report back if it is a ground issue.

It?s all good until it isn?t. I promised I would report back.
I apologize for my assumptions that a separate ground isn?t necessary. After more than 700 hours trouble free, things changed. I added a temporary ground for a long trip as I didn?t want to take out a screw, seal it, and then worry about a leak while the airplane was sitting on the ramp for a few days.
The temporary ground solved the issue. No more odd sender issues. A permanent, separate ground will be added this month during my CI.

Thanks Scott and Gary. As usual, ur right!

[sblack]

The instructions on my 1990 RV4 kit are sketchy. Is the recommendation to NOT use the rubber seal with the sender - just use proseal? I am just about at that step. This is a great thread.

Also, those toothed lugs are cool - where does one get those?

thanks for all replies on this great thread. I dunno what I would do without VAF.