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Q: Reinstalling fuel pump back into tank

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I had to replace my gas tank. Got stuck trying to reinstall the old fuel pump back into the new gas tank. There is a rubber gasket between the pump and the gas tank. No matter how hard i try I cannot press the pump deep enough into the gas tank to catch the threads evenly on the screw down ring. I tried gently tapping with mallet, I tried hitting it hard. I tried tapping with mallet using the lock ring as a bridge to apply even pressure and a block of wood, I tried it that way and hit it hard. I tried putting it in a hydrolic press with a die applying equal pressure around the pump, I cranked it like this until the the gas tank looked like it was going to fold. Even that didn't work. Should I try lubricant, what lubricant is safe to use inside a gas tank?
My car has a manual transmission.

If you are not using an OEM, dealer supplied gasket, but rather an aftermarket supplied gasket, that could cause this problem. The gasket you have may simply be too thick. Even if the gaskets are of the same thickness, there could easily be enough difference in the compression of the gasket, under load, as you try to install the lock ring, that it will be difficult. So, my first suggestion is procure an OEM gasket. In terms of seal lubricants, a slight film of engine oil will be harmless. If you use a silicon based material, just make sure there is not ANY excess that could get within the tank. Don’t use anything like grease. If you want these steps performed by a certified Mechanic, dispatched by YourMechanic right to your location, please request fuel pump installation and the responding mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic.

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