520H fuel gauge sender tweaked!

[Gary S Minnesota 57]

So, all gauges on my 1995 520H worked, except the fuel gauge.  No big deal but it kind of bugged me.  So, I ordered a Dorman 55818 Universal from Amazon.

I calibrated it according to the instructions, not to difficult. I then proceeded to remove the rear mounts of my Wheelhorse cab, then the seat and finally the seat pan fender assembly. I then removed the existing fuel sending unit and installed the new sender. I had checked the sender against the dash fuel gauge and the needle followed the sender float action nicely!  I then put everything back together, hopped in the seat and started the engine.

The fuel gauge pegged to the full reading immediately, but the tank was only 1/2 full?? 

What's the problem?

I got off the tractor, lifted the seat to remove the gas cap to confirm i didn't have a full tank and found the gauge now read 1/2 full. Mmm?  I got back on the seat and the needle again pegged to the full reading.

Next I played with raising and lowering the seat, noting that when the seat was up the gauge read correctly, when the seat was down it pegged to full.

Next I took everything off again to access the fuel sender for a look.  I determined that the brass "positive post" atop the sender was maybe a millimeter below the steel seat pan. Apparently, the weight of the seat assembly was

just enough to force the steel seat pan down to make contact with the positive post atop the fuel sender.  I grabbed my Dremel tool and a cutting disk and took about 1/4 inch of the brass post.  Wallah!!  it now works great!

If anyone uses that Dorman fuel sender you may want to trim that post initially and save yourself some time and aggravation?

[ebinmaine 71,801]

Excellent information Gary.  👌 

[lynnmor 7,703]

I wonder if you might have the usual amount of debris and rust caked under the tank.  It would have been a good time to completely remove the tank, clean everything and paint as needed.  If you find the fuel gauge slightly off when full or empty, know that the Dorman has slightly different resistance that can be corrected by filing material from the sending unit stops.

[Gary S Minnesota 57]

 

Interesting!  I hadn't considered that the tank itself may be slightly elevated.  I can see wear an accumulation of dirt and debris forced under the tank could raise it somewhat.

Thanks for the tip on filing the stops on the sending unit to improve accuracy.  The upper range appears accurate; I'll have to watch the gauge as the fuel level approaches empty..

On another subject; over the winter I removed and cleaned the carb ultrasonically.  The surging I had then disappeared completely.  While the carb was off I hooked up my compression tester and got readings of 110 on the rear and 95 on the front cylinders. (tested them both twice --cold of course).  I understand that 75- 125 is considered satisfactory.  is that cold reading OK or should I have tested the compression with a hot engine?

 

Thanks for your comments!

Gary

[lynnmor 7,703]

41 minutes ago, Gary S Minnesota said:

 

Interesting!  I hadn't considered that the tank itself may be slightly elevated.  I can see wear an accumulation of dirt and debris forced under the tank could raise it somewhat.

Thanks for the tip on filing the stops on the sending unit to improve accuracy.  The upper range appears accurate; I'll have to watch the gauge as the fuel level approaches empty..

On another subject; over the winter I removed and cleaned the carb ultrasonically.  The surging I had then disappeared completely.  While the carb was off I hooked up my compression tester and got readings of 110 on the rear and 95 on the front cylinders. (tested them both twice --cold of course).  I understand that 75- 125 is considered satisfactory.  is that cold reading OK or should I have tested the compression with a hot engine?

 

Thanks for your comments!

Gary

A bit carbon on the valves can cause low compression, run it hard for awhile and retest.  If you haven't adjusted the valves it would be a good idea to do that.