I was not happy with the instructions that came with the sending unit ring in that it gave a very small area to seal with, so I did something different:

I cut a slot in the ring so that it could be put through an opening the size of the inner hole of the rubber gasket.

Start one of the short screws to keep from dropping it, then use the long screw to get the float assembly started, then remove your helper screw.

This gives the whole gasket area room to seal, instead of just a tiny lip.

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Great idea! I did mine the hard way - have not put fuel in yet - worried if it will seal....

Leak check you fuel tank before installing it in the wing. If it leaks you can address it easy if its not installed. Put some gas in it and flip it on the end with the sender unit installed. Let sit over night...no leaks "Bob's your Uncle" empty the fuel into the gas can for the other fuel tank test.

What a great idea, wish I had thought of it before I struggled mightily with getting the gasket inside both tanks. 

Great idea. Fitting and sealing the sender unit was one of the trickiest jobs of all. My (larger)tank however came with my Czech kit with the sender fitted from a hole on the top. Why must it be placed on the side?

It does not matter if the sender goes in from the top or the side (on 601 planes for sure, and I believe on the other series as well). It is easier to service if it is on top (except you need to put an access into your leading edge) and it is a neater initial installation if you go in from the side. The factory has done it both ways over the years. You do need to bend the float arm correctly for the installation method. The float and arm need to go from empty to full and not bump into anything in between.

The way I leak tested my tanks was to pressurize them with just a few PSI of pressure using a bicycle tire pump.  A piece of clear tubing is attached to vent on the tank and run up a wall and filled with colored water.  If the water collum moves at all, there's a leak.  I let it stand overnight and looked that the level remained constant.  There proved to be a slow leak that was a devel to find and fix.

There are some details here:


Glad I found this before I did mine...

Excellent idea for installing fuel sender.  Has anyone successfully installed the fuel sender on the top of the tank instead of the side?  I am still debating on best place to put sender unit.  Any comments/pictures would be helpful.  Thanks.

It's been done, should be some photos here somewhere.  Wish I had done it. :(   Avoid putting them on the side like the plague...


I did install both the aux and the main tank fuel QTY XMTR  on the top  using a cover with a bumb to clear the hook up connection. I leak tested the installation with full fuel tanks but are still  many months away from flying  it.

Made sure by constructing a"jig" that the float does not touche  the fuel tank when there is no fuel in the tank  which may be often for the aux tank.

Replaced some of the steal parts of the fuel level XMTR with aluminum parts to reduce weight



Larry, I'm building a CruZer and installed from the top...sounds like maybe with the 650 there is room between tank top and skin without recessing but I had to recess, I used a VDO tube type sender. I used closed end rivets and pro-seal to seal everything tight and tested the tank for 7 days with 15 gallons of fuel in it (Bob MacDonald's idea of tilting is better). Also hooked up a gauge and 12 volt power to it to make sure the gauge worked properly...reading full when full etc. It actually was a lot easier than it looks.  If you do some search on the Cruzer or STOL forums you'll find a builder who found a sender that fits on top w/o having to recess.  Very happy with mine. BTW John Clark's idea is excellent if you must go sideways.


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