Gas caps: Harley thread or not?

[Donkey Hotey]

The gas caps on one of my bikes need chrome. I understand we all ran through the supply of NOS caps years ago.

Looking for something shinier and new, I noticed that Harley caps look suspiciously the same. Can anybody answer? Do the Harley dual-cap, right and left-hand thread caps work on our tanks? Joker Machine sells something that is pretty close to stock (knurled edge, chrome, the dome on top doesn't have quite the same shape).

[Donkey Hotey]

I figured I would follow up on this question. It cost me a whopping $15 to learn that--while they look very, very similar, even in your hand, they are not the same thread. The root thread diameters are the same but the major diameter is about 0.040" bigger and the thread profile is a wider circle than the Harley thread.

As a result, the Harley-compatible cap will start to thread in but, jams in less than one turn of the thread. Before anybody gets a cool idea to turn down the the major diameter of the threads, that doesn't work because of the difference in the thread profile shape. I had nothing else to do with these Harley caps so I tried turning the OD down. It just jams in the same spot. You'd basically have to make a half-round cutter tool, then rethread the plastic at--I think--4 threads per inch (IE: not for mortals).

[wytfut]

Lol

[ChadeArndt]

This is a useful post.  Thanks so much for the gas cap info Greg.  Now it just remains to be seen if there is a cap that will work if need be.

[Donkey Hotey]

I can't speak to ALL Harley compatible caps. It might be that the one I bought was on the weird side of the tolerance band. I don't have a bunch of money to buy gas caps, just to see if they fit.

The question was for two reasons: obviously, people could have their caps stolen in a parking lot. No clue why people do those things but, they do. The other is the chrome on some of our caps was very thin and it didn't take much to burn through.

I've already had problems finding chrome shops that will do small batches of parts and it's even harder if it's a replating job (taking off the old, polishing and replating). I really want to fix the caps on 1989.

[Jumper]

Remember!! The Fuel Tanks were made by BEHR in Germany... Therefore.. The threads "May" be Metric... Just thought I'd toss this little nugget of info out here...
I know of some Xer's that have switched over to "Custom" gas caps that pop up when you push them...
Jumper

 

[Donkey Hotey]

OK, if Behr made the tanks, who else do they make tanks for? Triumph? BMW? My guess would be yes.

You'd need to find a Triumph or BMW model that has left and right caps to verify. Then again, that would be a drastically reduced number of aftermarket caps to choose from.

If somebody installed the pop-up caps, that still suggests they made the Harley threads work. It could be done. Heck, it could be done with a little ball-burr and a Dremel if you had a steady enough hand to trim the threads down in the plastic cap.

No worries. More to come...

[blackheart]

FWIW....  I tried the cap off my 05 Victory TC & the threads match.  So it may not be any better for aftermarket support but the right hand thread cap works.

[Berlin Bob]

Harley caps do work ...both sides

[Donkey Hotey]

Bob, we're going to need more details. I posted my findings as a cautionary tale: the aftermarket Harley caps I bought absolutely and certainly do not fit our tanks. If you've found a different result, we need to figure out why yours worked and mine didn't.

What model did the caps come from, OEM or aftermarket, etc?