Stripped Thread in Gas Tank

[Bob_Blue_BJ8]

One of my fuel sender unit's screws backed out completely letting gas squirt into the jute mat soaking it and filling the garage with gas fumes. The screw is in good shape, but it won't tighten on the last few turns. The tank's threads must be stripped. Oh, and the paint on top of the tank is bubbled and peeling.

Questions:

1) How do I repair the tank's threads? Heli Coils seem too long. Is there a gas/ethanol resistant goop I can use?

2) What's the best primer and paint I can use on the tank?

Bob

 

[Michael Oritt]

Bob--

You might be better off filling the hole with a gas-proof epoxy product and drilling/tapping to the correct size. There are some high-tech products available but I believe plain old JB Weld will do the job. As far as a sealant goes I have found that a good cork gasket is all that is necessary, though using Hylomar on both sides of it would not hurt.

 

[Bob_Blue_BJ8]

Bob--

You might be better off filling the hole with a gas-proof epoxy product and drilling/tapping to the correct size. There are some high-tech products available but I believe plain old JB Weld will do the job. As far as a sealant goes I have found that a good cork gasket is all that is necessary, though using Hylomar on both sides of it would not hurt.

Thanks, Michael! Haven't seen you in a while. As a matter of fact, I just got the right type of Hylomar from Moss along with a set of gas/ethanol resistant gaskets for the NOS sender unit I bought a couple of years ago. The installed unit has never worked right since day one, so I figured I'd replace it as part of this repair job. Your suggestion of JB Weld is something I've been thinking about and may well try. I'll let you know if it works.

Any suggestions for priming and repainting the top of the tank? I was thinking about using some Rustoleum rust converter/primer. As for the paint, I'd like to find something that is gas/ethanol resistant should this happen again.

Bob

 

[dklawson]

My suggestion is to remove the sender and then tap the damaged threaded hole to the next larger fine thread fastener size. Drill out the corresponding hole on the sending unit flange for clearance and re-assemble.

Using all the fasteners you should not need sealant. However, if you want to use a pliable gasket sealant, use Hylomar or the Permatex equivalent.
EDIT: Permatex Permashield #85240

When you say the replacement parts have never worked correctly, does the tank/sender have a good ground connection? You can make one by crimping a ring terminal to a length of wire. Secure the ring terminal to the sender using a sending unit mounting screw. Attach the other end to the car's chassis.

 

[Bob_Blue_BJ8]

My suggestion is to remove the sender and then tap the damaged threaded hole to the next larger fine thread fastener size. Drill out the corresponding hole on the sending unit flange for clearance and re-assemble.

Using all the fasteners you should not need sealant. However, if you want to use a pliable gasket sealant, use Hylomar or the Permatex equivalent.
EDIT: Permatex Permashield #85240

When you say the replacement parts have never worked correctly, does the tank/sender have a good ground connection? You can make one by crimping a ring terminal to a length of wire. Secure the ring terminal to the sender using a sending unit mounting screw. Attach the other end to the car's chassis.

Thanks, Doug. The Hylomar arrived from Moss yesterday. Since I don't have a good tap and die set, I'm going to try the J B Weld first. I figure putting a little in the existing threads, letting it cure and then chasing it with the screw might work. Failing that, I'll have an excuse to buy a good tap and die set! :wink-new: I will definitely take your suggestion for grounding the sender unit to the chassis! I've been thinking about that for a long time. A friend with another BJ8 gave me the measurements for a dipstick that gives you the exact amount of gas in the tank. It NEVER fails! Kinda hard to use while moving though.

Bob

 

[Bob_Spidell]

I think tapping oversize is probably the best option--though, IIRC, you don't have a lot of 'meat' on the sender flange for strength--but you can try something like this:

https://tinyurl.com/yagkukxf

I used something similar when I stripped the threads on the clutch slave cylinder boss on my BJ8's bellhousing--steel bolt into aluminum hole; whose idea was that?!--and it held for many years, until I put proper thread inserts in recently.

The sender for my BN2's tank had a warped flange; some ham-fisted shadetree mechanic--not me, for once--had torqued the snot out of the screws, apparently trying to stop a leak like yours. We straightened the flange out best we could--you can't bend pot metal much--but it still leaked. Tried all manner of gaskets, but what worked was stacking two cork gaskets on top of each other, with a thin coat of this stuff on both sides of each (of course, I had to use longer screws):

https://www.permatex.com/products/g...uel-resistant-gasket-dressing-flange-sealant/

As for the paint, I don't think rust converter is necessary--though it seems to work well--unless the tank is, well, rusted. Just sand the bare metal and whatever paint is left, clean with a good oil/grease remover, spray a good primer/sealer then a good, automotive color coat. If you're getting water/rust in the boot you need to fix the leak(s).

 

[Bob_Blue_BJ8]

I think tapping oversize is probably the best option--though, IIRC, you don't have a lot of 'meat' on the sender flange for strength--but you can try something like this:

https://tinyurl.com/yagkukxf

I used something similar when I stripped the threads on the clutch slave cylinder boss on my BJ8's bellhousing--steel bolt into aluminum hole; whose idea was that?!--and it held for many years, until I put proper thread inserts in recently.

The sender for my BN2's tank had a warped flange; some ham-fisted shadetree mechanic--not me, for once--had torqued the snot out of the screws, apparently trying to stop a leak like yours. We straightened the flange out best we could--you can't bend pot metal much--but it still leaked. Tried all manner of gaskets, but what worked was stacking two cork gaskets on top of each other, with a thin coat of this stuff on both sides of each (of course, I had to use longer screws):

https://www.permatex.com/products/g...uel-resistant-gasket-dressing-flange-sealant/

As for the paint, I don't think rust converter is necessary--though it seems to work well--unless the tank is, well, rusted. Just sand the bare metal and whatever paint is left, clean with a good oil/grease remover, spray a good primer/sealer then a good, automotive color coat. If you're getting water/rust in the boot you need to fix the leak(s).

Thanks, Bob. I appreciate the link to the Locktite product. However, it doesn't say it's gasoline/ethanol resistant. Actually, here's a link to it on Amazon where a user complains it turned soft in a carb fix. https://www.amazon.com/Loctite-442-28654-4-80ml-Thread-Stripped/dp/B000WSEUII

You're probably right about tapping to the next size up. But, as I said, I don't have a tap and die set (yet). I have dug out my old tubes of J B Weld though. It says it's good for gas tanks (at least it won't dissolve). If it doesn't work on the thin gas tank sheet metal, I GET TO BUY A NEW TAP AND DIE SET! I can then honestly tell the spouse that I tried cheaper fix that didn't work. The nice thing about being retired is that I can fool around with this stuff all I want.

I have no idea how a prior owner had torqued the screws enough to bend your sender unit flange without stripping the tank threads first.

Thanks again,
Bob

 

[steveg]

If you get 10-32 and 1/4-28 taps, that'll do 95% of the Healey. The screws we're discussing are 10-32.

 

[dklawson]

If you get 10-32 and 1/4-28 taps, that'll do 95% of the Healey. The screws we're discussing are 10-32.

A lot of SU and Smiths fuel system components use BA threads. If the sending unit threads appear to be 10-32, they may actually be 2BA which has a major diameter only about .004" smaller than 10-32.

For your first oversize, you can try M5. M5 fasteners will be about .008" larger than 10-32 and .012" larger than 2BA. In fact... why not just TRY an M5. You may find it fits what is left of the threads without having to use a tap at all. As stated above, you don't have much material thickness there. The slightly larger M5 screw might just form its own new threads going through.

You can invest in individual taps and dies as you need them. Most British cars use UNF threads for the majority of fasteners. As mentioned above, you can start with 10-32, 1/4-28, 5/16-24, and 3/8-24. Though much maligned, you can get acceptable tap and die sets from Harbor Freight and similar places. You want alloy steel (high speed steel), not tungsten steel or low carbon steel. Do not buy a set unless the taps and dies have a bright, ground finish. If you anticipate making new threads, avoid sets sold as "re-threading" kits. They are aimed more at cleaning damaged threads than creating new ones.

 

[steveg]

The threads are in the tank - sender just has holes. I've been running 10-32 panheads with bonded sealing washers for 12 years:

If the M5 is going to work, you could make an impromptu tap out of an M5 screw:

 

[Bob_Spidell]

Thanks, Bob. I appreciate the link to the Locktite product. However, it doesn't say it's gasoline/ethanol resistant. Actually, here's a link to it on Amazon where a user complains it turned soft in a carb fix. https://www.amazon.com/Loctite-442-28654-4-80ml-Thread-Stripped/dp/B000WSEUII

Good point; didn't think about that.

 

[dklawson]

The threads are in the tank - sender just has holes.

Sorry. That was a poor choice of words and sentence structure on my part. I know it is the tank that is threaded... not the sender.

 

[Healey 100]

I have used JB weld around gasoline in carburetors and can report that it definitely softens and cannot resist gasoline or ethanol. Most fiberglass resins seem to hold up rather well, I have made several gas tank patches with fiberglass that have held up for years.

Those threads on that flange are rather limited in depth, not much work with. Suggest you find a sheet metal screw that is large enough to cut its own threads into the sripped hole in the flange. You may have to drill out the bad hole in the sending unit to do that. Remove the sending unit if you do any drilling around that tank, there are horror stories about what can happen working with power tools around gas tanks.

 

[Deleted member 19315]

I would over drill the hole and fit a countersunk rivnut sealed into place with Petseal. A new cork gasket too.
Andy

 

[dklawson]

Just a couple of concluding points before I bow out.

Yes indeed, be careful when working around gas tanks with power tools. However, if you leave the sender in place and leave the gas cap in place you will be OK drilling and tapping the tank IF tapping is required at all. Gas tanks do not regularly explode because the fuel/air mixture inside is overly rich. This is why fuel gauge sending units do not cause explosions either during normal operation or when the sending unit fails. It is also why you cannot get a mixture to ignite when you flood an engine. The fuel/air ration has to be right for ignition.

Yes, the material is thin so tapping the tank may sound tricky. However, the factory used machine screws not sheet metal screws so you shouldn't have to resort to a different fastener type. As I mentioned, an M5 may form its own threads during installation without the use of a tap. In industry it is very common to use what are know as form taps. These don't remove material they push the material into place to form the threads.

Rivnut inserts are indeed a possibility. However, if you install one you might as well do them all. The downside is that the rivnuts have heads which will make it more difficult to achieve a good seal with a stock sending unit gasket. You may get better results making your own gasket from thicker material if you take this route.

 

[Bob_Spidell]

I would over drill the hole and fit a countersunk rivnut sealed into place with Petseal. A new cork gasket too.
Andy

Best idea yet, assuming the gasket can seal the raised part of the rivnut.

 

[steveg]

10-32 rivnut with tank gasket

 

[Bob_Blue_BJ8]

If you get 10-32 and 1/4-28 taps, that'll do 95% of the Healey. The screws we're discussing are 10-32.

Thanks, Steve. I'll keep that in mind if I don't feel like going with a more complete kit. BTW, I enjoyed browsing your galleries! Lots of great ideas and innovations for Healeys!

Bob

 

[Bob_Blue_BJ8]

A lot of SU and Smiths fuel system components use BA threads. If the sending unit threads appear to be 10-32, they may actually be 2BA which has a major diameter only about .004" smaller than 10-32.

For your first oversize, you can try M5. M5 fasteners will be about .008" larger than 10-32 and .012" larger than 2BA. In fact... why not just TRY an M5. You may find it fits what is left of the threads without having to use a tap at all. As stated above, you don't have much material thickness there. The slightly larger M5 screw might just form its own new threads going through.

You can invest in individual taps and dies as you need them. Most British cars use UNF threads for the majority of fasteners. As mentioned above, you can start with 10-32, 1/4-28, 5/16-24, and 3/8-24. Though much maligned, you can get acceptable tap and die sets from Harbor Freight and similar places. You want alloy steel (high speed steel), not tungsten steel or low carbon steel. Do not buy a set unless the taps and dies have a bright, ground finish. If you anticipate making new threads, avoid sets sold as "re-threading" kits. They are aimed more at cleaning damaged threads than creating new ones.

Thanks, Doug! I'll try M5's before messing with J B Weld. I'm can't believe how many responses I'm getting to this post, all good. Brit car guys are the best!

Bob

 

[Bob_Blue_BJ8]

To All Who Have Replied to This Thread,

Thanks again for all of your help. You guys are great! I'm off now in search of 7 M5 screws with bonded washers (hoping I can find washers that will fit the holes near the corners of the sender unit body). BTW, before you tell me I only need six, the 7th screw will be the sacrificial screw for making the tap Steve suggested. I'll be putzing with it tomorrow and will let you know how I make out after driving for a bit.

Bob