I am at the point on my CH 750 where it's time to install the sending unit for the fuel gage.  I admit that I have been putting it off for fear of attacking that beautiful aluminum tank with power tools.  I know you other builders have done it hundreds of times.  I could use any tips on the tools used, keeping debris out of the tank, holding the tank steady, etc.

Thanks for the comments, this is my first airplane project.

Dan Coates

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Comment by Rebecca Anne Shipman on February 7, 2013 at 3:25pm

I was really nervous doing this, too.  I toyed with the top of the tank concept, but decided to go with the plans.  I used a flycutter, set it slightly undersize, and practiced on a scrap piece first.  One of the things I tried hard to do was get all the cuttings out of the tank - I used duct tape and a stick to grab and pull them out.  I used a bunch of fuel lube as well.

Good Luck!

Comment by Geoff Klestadt on February 7, 2013 at 2:52pm
I did mine with a fly cutter in a hand operated brace and bit.

I also very messily sealed the unit in place by smearing AC240-2B fuel tank sealant on both sides of the gasket. Fuel tank sealant cures to a very tough rubber that is impervious to everything.
Comment by Roger Wibbels on February 7, 2013 at 2:05pm
I put mine on the top as well with a non-conductive cover. very accessible and not prone to leak.
Comment by Phil Smith on February 7, 2013 at 11:08am


I had the same trepidation as you.  First, if I was to position the sensor again I would take a close look at putting it on the top of the tank. Seems to make sense from a  leakage standpoint and serviceability. Haven't had any leakage problems - yet - but it is in a very inaccessible place that would of course require the the removal of the root fairing to check AND then the possible removal of the tank to fix a leak. So hope all that I did to seal it up works.  As for the drilling of the hole I was also in a quandary about how to do it.  I scribed a slightly smaller hole on the tank and drilled it around the inside of the mark with a #30 drill. Use the diameter across the min dimension for the notch. Might practice with a scrap piece first Probably over kill but I was able to carefully move the ID out with a file and dremel tool to where I could just fit the gauge   If you go to the hole speced it will be somewhat bigger.  About the filings and all...I washed and washed the tank with solvent until no more chips etc came out.  After 70 hours on the plane I haven't had a problem.  Oh yeah, I plugged the tank outlet and filled it with gas and let it sit in the sun for a couple of days before I was satisfied it wasn't leaking.

Questions email me 



Comment by Paul Toone on February 6, 2013 at 7:26pm

Hi Dan,

I've just replaced the sender on my 601XLB after the original went open-circuit.

Unsure where the plans show the sender on your aircraft but I'd strongly advise you think about installing in the top of the tank rather than my original, in the end of the tank.

I made a plate to cover the hole and it seems to be good. At least it gives fuel readings now.

Coat your hole cutter with a good grease. It really collected most of the debris from my cut.



Comment by Tracy Buttles on February 6, 2013 at 3:54pm

Practice on some scraps , the  guage does not have alot of edge distanec to seal really good , so  try to get that hole as small as possable and still get the guage in .That guage is from a VW bettle and originaly designed to be on top of the tank , now on the side the fuel is constanlly tring to  find a way out. The older 701 kits and the extended tanks on an 801 put that guage on top the tanks , that would leave the need to make covers on top the wing skins.

Good or bad  ,who knows  .I have had some leak around the screws  .Make sure the washers are copper and use some sealent on the threads

Comment by Jesse Hartman on February 6, 2013 at 2:45pm
There was a guy that just posted a picture of his sending unit hole that was about hald the size of everyone elses. look up in history you may like it this way. Its the way I'll be doing it.
Comment by Paul Sanders on February 6, 2013 at 2:22pm

Dan, I had the same thoughts and probably put it off for about 6 weeks before I bit the bullet. I bought a metal hole saw that was just a little bit smaller than the hole that is required (on the assumption that I would mess it up) and then used a small file to enlarge the hole so that the sender would fit.

As for technique, I just grabbed the fuel tank firmly between my knees and drilled the hole :) It was much easier than I expected and in retrospect wished I had bought the proper side hole saw and save myself a lot of filing. I don't think you can keep debris out of the tank but I did my best to shake it out, followed by a gentle air blowing. 

If you do a search for sender you can probably find a thread where I asked the same question and there was a discussion on it.

I'm a complete beginner when it comes to this plane building and using any tool other than a hammer so if I could do it, I have no doubt you can too.

Good luck.

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