MTFCA Forum

Using the yellow compound, how much and how hard do you need to lap these leaky brass petcocks?

I have never been successful lapping the valves, I have had better results with aircraft fuel valve lube.

Use tooth paste. Use enough with water to lube. Allow the compound to work. Forcing will not get the job done.
Really bad petcocks can be started with a fine lapping compound. Its real easy to go to far & end up with scrap brass.
Toothpaste & patience has worked best for me.

My experience has mirrored Jeff's above. Latest venture using the valve lube sold by Langs did the trick on a brass fuel shut off that continued to leak after lapping with yellow Timesaver. It's not cheap but it works!
I agree it's easy to lap too aggressively and ruin the piece. Been there, done that.

Fuely lube has been my choice. Not much luck with lapping but got them closer before using fuely lube. A bar of soap works too if you are frugal.

How do you use a lube to stop the leaks? Wouldn’t it dissolve eventually?

It's really gooey and doesn't dissolve easily.

I used EZ turn fuel lube from Spruce aviation long before the antique auto supplier's had offered it. It is used in the aviation industry for fuel valves with high octane. It's been working for years on my valves and I use it on some gaskets as it's easy to remove them. Before that I had tried ever pipe sealant I could find and nothing held up but a bar of soap worked quite well.

Hi Jason,
I have not had good luck with fuel petcocks & timesaver. Had good luck with oil & water petcacks. The aviation valve grease is great stuff
I use it religously. I have not tried tooth past but makes sence, I have used Fast Orange hand cleaner to lap firepump pressure relief valves
before, in a pinch worked pretty good.
Craig.

What about silicone or dielectric grease?

My father and I used bar soap to lubricate the fuel shut off valves and respective petcocks on our Ts.

It's not affected by gasoline and lasts a long time.

Jason, the aviation EZ lube is designed specific for lubrication of fuel system components and won't dissolve in gasoline, soap does the same, used it to fix leaking valves on everything from bikes to trucks, even made a temporary fix once on a carb float that had a small leak, just smeared the little hole with a bar of regular soap and drove the bike home for 50 miles or so, worked like a charm !

Soap is corrosive, I wouldnt recomend it for a Model T fuel shut off valve.

Old trick, push in as you shut off rather than just turn.

EZ turn works, but I find that I have to disassemble the valve and reapply the EZ turn once a month or so. No big deal.

Humblej wrote: ↑

Thu Sep 21, 2023 8:08 am

Soap is corrosive, I wouldnt recomend it for a Model T fuel shut off valve.

I have not found that to be the case. Works well for me. It only takes a tiny amount. I thin coating on the tapered shaft, being careful to NOT get any tiny shavings of soap in the hole, has lasted for years. Just rub the bar soap on the shaft in a couple of spots. When you rotate the valve it will distribute as needed. Again, a tiny amount. You don't want any soap particles getting loose and going into your carb!

Still wouldn't hurt to do some fine lapping to get things running closely. Do a little lapping, then look at the shaft and in the hole to see if the surfaces look dull all over, signifying that full contact has been achieved. If there are still areas that lapping has not affected, repeat and recheck. Having a dull/lapped surface and full contact can make the valve "sticky". A tiny bit of soap will help to lubricate it.