Gas Tank Bump

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Gas Tank Bump

Postby JerrryR » Tue Oct 26, 2021 11:32 pm

A friend pointed out to me something I had never noticed, the little bump the yellow arrow is pointing out. Does anyone have any idea why the little bump exists?

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Re: Gas Tank Bump

Postby 44UL » Wed Oct 27, 2021 12:29 am

I’ve noticed them and thought they are similar to the bump on the rear tip of early panhead gas tanks.
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Re: Gas Tank Bump

Postby hayleyl » Wed Oct 27, 2021 1:10 am

Hello boys & girls - I believe the bump you haven your tank is a welded up hole from when the tanks are manufactured. It's a drain hole for what ever chemical the factory lines the raw steal tank with - I think it's sort of like a parkerising process - there's another name for it but can't think of it at the minute. Genuine shovelhead tanks have the little bumps underneath right down in the back corners. I reckon they stopped that process in about 78 or 79 but don't quote me on that. I could assume panhead tanks were manufactured using the same process. I've seen lots of sportster tanks with the same little bump, some more pronounced than others. Cheers Hayley.
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Re: Gas Tank Bump

Postby Rubone » Wed Oct 27, 2021 10:03 am

hayleyl wrote:Hello boys & girls - I believe the bump you haven your tank is a welded up hole from when the tanks are manufactured. It's a drain hole for what ever chemical the factory lines the raw steal tank with - I think it's sort of like a parkerising process - there's another name for it but can't think of it at the minute. Genuine shovelhead tanks have the little bumps underneath right down in the back corners. I reckon they stopped that process in about 78 or 79 but don't quote me on that. I could assume panhead tanks were manufactured using the same process. I've seen lots of sportster tanks with the same little bump, some more pronounced than others. Cheers Hayley.

They called it "Bonderizing" for certain parts along with "Parkerizing", and the bump is on all the welded tanks on all models from '36 up I've ever inspected.
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