1985 K100 fuel leak at sending unit- replaced the rubber gasket and still leaks

[Wheezyryder]

outer

[Laitch]

The nut is captured by a flange on both sides

A flange on both sides of the sender's body? Please clarify. In my opinion there should be some captive arrangement of the nut to the sender body—a flange on the body that snaps them together or a firm friction fit.

I'd apply a thin coat of sealant to the clean mating surface of the sender flange that contacts the outer surface of the nut, run the nut up the sender until the nut mates with the sender's flange, install the gasket until it seats on the nut, firmly press the assembly into the port so the sender's shoulder fits into the port and the nut's threads are at the point of engagement, then tighten the nut with one hand while pressing the sender with the other.

When viewing photographs of a round or cylindrical part, it's helpful to have enough of them to evaluate the entire perimeter of the part.

[The Mighty Gryphon]

With the sender out of the tank is the nut square to the sender body when you press it down on the flange that bears against the outer edge of the spigot?  ie. Is there something between the nut and the flange it is bearing against?

Did you run your finger around the inside of the spigot to feel if there are any imperfections that can hang up the sender?

Is the nut staying square to the spigot as it's being screwed down?  ie.Are you absolutely sure it isn't cross threaded?

What you describe as the sender cocking as the nut gets to the end of it's travel makes me think the sender is either binding in the spigot or there is something between the nut and the flange that bears against the gasket.  The only other possibility is that the bearing surface at the mouth of the spigot is not square with the bore of the spigot or the flange on the sender isn't square to the body of the sender.

[rbm]

With the sender out of the tank is the nut square to the sender body when you press it down on the flange that bears against the outer edge of the spigot?  ie. Is there something between the nut and the flange it is bearing against?

Did you run your finger around the inside of the spigot to feel if there are any imperfections that can hang up the sender?

Is the nut staying square to the spigot as it's being screwed down?  ie.Are you absolutely sure it isn't cross threaded?

What you describe as the sender cocking as the nut gets to the end of it's travel makes me think the sender is either binding in the spigot or there is something between the nut and the flange that bears against the gasket.  The only other possibility is that the bearing surface at the mouth of the spigot is not square with the bore of the spigot or the flange on the sender isn't square to the body of the sender.

This is what I was implying by asking my questions in post #41.

[alabrew]

It has been over a year since I have the sending unit out of Big Red and replaced that gasket, so I am a little fuzzy.

No issues at all that I recall. I put the gasket into the nut and made sure it was fully seated and the nut turned freely.
I assume Pic #2 shows the gasket removed and the room for the gasket between the stem and nut.
IIRC, I installed it with the tank upside down, so the hole was level and snugged it tight.

I do not see where you attempted to install the sending unit without the gasket to see how far it can be installed.


Interesting, Max fiche lists the part as a "Gasket Ring" and it is flat, but then they further describe it as an "O-Ring"

06    61 31 1 459 448    GASKET RING        1     $1.45ADD TO CART
Part Thumbnail Part Thumbnail
Part Thumbnail
O-Ring, K75 - K1100RS.

I can not find any application for a K75 or K1100RS, only K100

[Laitch]

Interesting, Max fiche lists the part as a "Gasket Ring" and it is flat, but then they further describe it as an "O-Ring"

The fiche also has labeled the rear drive diagram as a Differential, which it certainly isn't—an example of Germglish 101.

[Wheezyryder]

Alabrew- I'm pretty sure that my sending unit is damaged in some way. But since I haven't seen one that isn't damaged it's difficult to tell. Do you still have your '85 K100? Can you look at the sending unit and see if the flange with the arrow on it has a gap between it and the nut? Like the one in this pic. That would confirm that mine is damaged.

If I can confirm that it's damaged then I can confirm that I need to try something unconventional to fix it. My plan is to first try doubling up the gaskets. Maybe even tripling. If that doesn't work then I'll try the fuel proof thread sealing tape. If that doesn't work then I'll try a fuel proof RTV sealant. And if that doesn't work then I'll try to find a used sending unit, which seems like a difficult thing to find according to my research.

[Laitch]

I'm pretty sure that my sending unit is damaged in some way. But since I haven't seen one that isn't damaged it's difficult to tell.

If you want to compare some, look on the Web. I've seen more of them than I imagined possible with my short attention span, and all of the flanges seemed flush with the nut. That's why using sealant under the flange was suggested if there wasn't enough muscle to push it flush with the top of the nut, or if the flange of the sender was somehow out of square with the sender's body.

[Wheezyryder]

Laitch-  I did some searching on the web. Found pics of the sending unit part itself but not installed. So I wasn't sure what it should look like installed.

[Laitch]

Laitch-  I did some searching on the web. Found pics of the sending unit part itself but not installed. So I wasn't sure what it should look like installed.

The sender flange is supposed to be flush with the top. If you can't force the cap up to the flange with the sender body inverted then you'll need to try sealing that the gap with RTV or another sealant because that's where you indicate it's leaking. Wrapping the outlet threads with tape or applying paste to them is unlikely to stop a leak from a gap in the flange/nut mating surface. Once you get it installed there is a 50/50 chance it won't work correctly anyway because that style was notoriously unreliable—the reason the float-style was introduced in 1986.

[alabrew]

Wheeze - yes, still have the '85, well, two...butts, that's another story.

Yes, there should not be a gap between the stem and nut with a gasket in place.
In your last pic., it really doesn't look like you have it screwed down all the way.
No threads should be visible, especially without a gasket.

[Wheezyryder]

Alabrew- Thanks! I was wondering about the exposed threads as well but forgot to ask about that. I guess that whatever is making it crooked is also keeping me from screwing it down all the way. I'm just nervous to put too much torque in the nut because if I break it I've opened up an even bigger can of worms.

My new gaskets should arrive tomorrow and then I'm gonna give it another attempt.

[Laitch]

I was wondering about the exposed threads as well but forgot to ask about that. I guess that . . ..

There are usually a few exposed threads on the end of a capped pipe. Take a moment to analyze this thing instead of guess about it.

The molded flange of the sender should seat on the top of the gasketed nut. In that position, the sender unit should screw tightly onto the port. There should be no leaks from the around the port's threads nor or the seam between the joint and the cap. You've neglected to answer some questions posed in this thread previously. Please answer these.

• Without the nut on the sender's body, can the sender be pushed into the port all the way up to its flange being level with the port's external opening?
• If No, can you see what is obstructing it by looking into the opening of the fuel tank with its cap assembly removed?
• Can the nut be slid all the way up the sender body until it's surface is flush with the entire underside of the flange.
• If No, what's stopping it?
• If Yes, will the nut stay in that position when the sender is held vertically with its socket upwards?

Tightening the nut is unlikely to draw the sender's body down until its flush with the nut nor prevent fuel from leaking from a gap left between the flange and the nut, as you have described the leak. Excessive tightening could crack the plastic nut.

[Wheezyryder]

Laitch- I'll try to answer in order and as best I can:

1) It is not possible to remove the nut from the sender body. It is captured in between 2 flanges that are part of the sender body. So it isn't possible to insert the sender without the nut. It seems like whatever is causing the sender to seat crooked is between these 2 flanges, and I can't see in there to determine what it is.

2) When the nut is slid up the sender body against the inner flange, it becomes crooked. I can't see in there to determine what is keeping in from seating evenly.

[alabrew]

I took the sending unit off the parts bike last night.
There were some threads still showing while it was installed.
I did not remove the gasket that was installed because I saw there were only three in the bag, I had both 5, so I didn't want to risk damaging it.
With the gasket installed, there is fair amount of friction between the nut and stem.

Are you installing the gasket between the nut and the lower stem flange, or are you attempting to have it seat when you screw it in?

I inserted it inside down to show its correct orientation. =-}

[Laitch]

There seems to be a distinct difference between the depth of Alabrew's sender nut and the depth of Wheezy's sender nut. Maybe that's a function of photo perspective or maybe they are two differing assemblies.

It should be possible to use a thin, angle pick between the flanges surfaces to search for and remove obstructions. It should be possible to inspect through the sender hole and the fuel tank cap assembly hole using a flashlight and an articulating mirror to search for obstructions. It should be possible to try the sender's mounting with the gasket in two different positions as Alabrew has indicated.

If none of this is possible, then buying and installing a used sender and hoping for the best, or sealing that outlet by whatever means are available and computing remaining fuel supply by mileage are other options

Onward!

[alabrew]

Are you SURE you have all the old gasket out?
I seem to remember the nut flopping loosely without the gasket.

[daveson]

Getts you some lube on the gasket, including the inner diameter (am I the only one missing the Johnny speak here?) so it doesn't bind on the threads and travel up the thread, cocking the gasket with the thread. Push the gasket fully into the nut, past the threads. Push against the electrical socket with your thumb to prevent the gasket engaging with the thread.  With your thumb pressing on the socket, then turn the nut. Give that a go. Might be lucky.

If you have the gasket off, check there is no split between flange and sender in case sender goes off right angles, causing the coned part to jam in the tank opening, preventing the nut from compressing the gasket, or all around the gasket.

When it's installed does the unit feel solid inside the tank, or a bit wobbly, in which case maybe it can be straightened to tighten some more.

The gap between the lower flange and the nut is a hint that the gasket might be engaged with the threads.

[Wheezyryder]

FINALLY GOT IT TO STOP LEAKING!!!!!!!!!!!!!!!

Apologies for the delay in getting back to this thread. Last weekend was my son's 2nd birthday and we went camping for the weekend. Then work, house repairs etc. But the good news is that it looks like the leak is finally resolved. After trying various method of trying to stop the sending unit from getting crooked, doubling up the gasket, and using a fuel resistant thread seal tape on the threads, I resorted to the method I was trying to avoid. I used a fuel proof sealant called Seal All. If this had not worked I'd be hoping to miraculously find a used sending unit on eBay.

That particular sealant was recommended by a friend that repairs small engine equipment for a living. He says he's used it to repair plastic and metal fuel tanks, fuel inlet nipples and other parts that are in constant fuel exposure and vibration and has had success with it. Says the repairs have held up over time and use.   I used a Dremel with a brass brush to clean and scuff the surface between the outside of the nut and the outer flange. Then further cleaned all surfaces with acetone and compressed air. Then I applied the sealant to both sides of the gasket and to the gap between the outside of the nut and the outer flange. I pushed the sealant into the gap with a cotton swab dipped in a bit of acetone.

The downside of using the sealant is that if I ever have to remove the sending unit for any reason it'll be a bit of a cleanup job. And since the nut no longer will rotate independently of the sending unit, I'll have to disconnect the wires from the fuel pump before unscrewing it. Hopefully this repair holds up long term. I'm excited to finally be able to button this thing up and take it for a first test ride since I bought it.