Petrol tap - how to fix a stiff tap
- by Nick Beck
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I fitted a petrol tap to my chummy that was the taper plug type. Knowing that they are inclined to get stiff I lubricated the plug with molybdenum disulphide when I fitted it to the car. Even so it became very stiff to operate and I think that this is because the plug and body of the tap are of similar metals.
I decided to try a different approach to lubricating it by coating the plug with lead solder. With the fuel tank very low I ran out enough petrol so that I could remove the tap and take the taper plug out. Then I “tinned” the taper surface with tin/lead solder. I did this by coating it with the solder and whilst it was still hot and the solder molten, used a cloth to wipe the excess solder off. This left a very thin coating of solder, much the same as though it had been plated. I made sure that there wasn’t solder on the thread etc. that compromised the assembly and re-fitted it to the car.
A few weeks on and the tap works well and is easy to turn without that dreaded creaking noise. Lead has often been added to metal alloys as a lubricant to make them easy to machine so whilst a modern lead free solder might have a similar affect I think that the lead is important. I have done a similar job on the radiator tap as I couldn’t turn that by hand and that has had the same result. See the photograph of the plug from the radiator tap.
I used a very large electric soldering iron to do this job and small one would probably not get the plug hot enough. A small gas torch would be OK.