NOS gas cap doesn't fit properly

[jbjeeps]

As I reported at the beginning of the summer, the old gas cap on the A1 leaks.

Now that summer's over and the A1 is back in the garage the fumes are once again getting into the house. Patience is low on this issue and it is about to be permanently evicted to the backyard!

So, I bought what was described as an "NOS" cap that had been made in the "1970's" on ebay.

Here's a picture of the old and the new



The new cap doesn't fit properly. The ears on the inside of the cap don't properly engage the ring or the locking tabs on the inside of the gas tank filler neck. It is as if the locking ears are too short. When I put the new cap on the tank, it just spins, without coming to a stop at the tabs like the old one does.

I pulled up a chair and sat out in the backyard next to the A1 and tried all my best magic, but couldn't get the cap to fit properly. Darkness ended my efforts.

I haven't taken precise measurements, but using my ruler it looked as if both caps are the same size and distances between locking ears appear the same.

Judging from the appearance of the gas tank, I'd say it is an original tank, certainly not a recent reproduction. If it is a replacement, it was replaced a long time ago.

Maybe it's not the cap, maybe the filler necks on early tanks were slightly different size.

Boise winters can be pretty soggy. I prefer the A1 to be inside. I may just drain the tank, air it out and then push it back into the garage.

Anyone have similar experience with gas caps? Any solutions?

[Wiltshireboy]

Why dont you try taking the new rubber washer and putting it on the old cap? Its worth a try to avoid all the work draining the tank.

[RICKG]

Jack, i have 2 caps for my M-38.. the vented one fits poorly and
doesn't engage properly, sounds like what you're describing.
However my pressurized cap fits snug as a bug
I see you're running the vented cap. It's hard to tell
from the photo but are both valves in the same position?
My vented cap fits better with the valve closed for fording.
BTW- i'm headed to Weiser this weekend for a saddle mule auction,
if i was traveling solo i'd stop for a visit but my wife doesn't
speak Willeze.

[jbjeeps]

Jack, i have 2 caps for my M-38.. the vented one fits poorly and
doesn't engage properly, sounds like what you're describing.
However my pressurized cap fits snug as a bug

Really? And your Jeep is parked where?

Seriously, is the one that fits well new or used? Where'd you get it?

[RICKG]

Jack, in the meantime i revised my earlier reply-take another look.
My jeep is parked in my detached barn, a previous milking barn,
the "man cave". No problem with fumes there. No segregation
here tho-females are always welcome-just bring beer and nachos
Both my caps are used and came with the project..

[jbjeeps]

Jack, in the meantime i revised my earlier reply

Yeah, the problem with the old cap is that the internal valve is rusted and doesn't turn. I don't know if it's rusted open or rusted closed. Andy suggested that I could put the new gasket on the old cap. I may do that, but first I need to make sure that the tank vent to the carb is clear and working, otherwise, I think that sealing the cap will create a vacumn and prevent fuel from flowing to the engine.

We'll be around this weekend. Doing cleanup after some remodeling and trying to get all the "junk" out of the garage in the morning, watching the game (Go Broncos!) in the afternoon.

Saddle mules? I worked on the south rim of the Grand Canyon for 6 summer seasons. It was sometimes entertaining to go to the trailhead in the afternoon and watch the dudes try to get off the mules after riding all day.

[RICKG]

Yeah, Jack-mules are my "other addiction"
Here's me and my sweetheart "Fiona"

[jbjeeps]

Very nice, that is a good looking animal! Old Jeeps and mules are a good combination for enjoying the backcountry.

[wesk]

The 4 or 5 different M series caps are designed to interchange on all the M series tanks which used a standard filler neck on all of them. If the cap you got will not fit then either the cap is a repop or bad batch of NOS or the tank is a repop with a poor reproduction of the filler pipe.

Below are two photos of a correct NOS vented cap. Notice how the chain is fastened and how the positions for the valve are marked.





Have you tried freeing up the valve on your old cap using PB Blaster, a little soaking time and gentle working back and forth?

[jbjeeps]

Thanks for your reply Wes. The cap I have looks like the one in the photo you posted except that mine doesn't have the numbers and little round symbol stamped on the inside like yours.

[wesk]

Can you post the dimensions for A, B, C & D?

Your new cap looks to be a repop. It could be NOS. NOS parts from the military surplus system often include both correct parts and seconds or misfits that did not fit and were turned in to base salvage and made their way to the DRMO.

[jbjeeps]

A = 3 7/16
B = ?
C = 3 7/16
D = ?

I don't have a good way to measure for B and D.

But, I just went outside and tried the new cap again and realized something. The inside part of the cap, the gold colored part with the locking ears, valve and chain, is not SOLIDLY attached to the outside shell of the cap. It's tight, but not solid. So, when I put the cap on the filler neck, grab the large ears on the outside and turn them to close the cap, the inside doesn't turn with the outside. That explains why I felt last night that the locking tabs on the cap were spinning past the locking tabs in the filler neck. It wasn't because they were going past each other, it is because the inside of the cap isn't moving when I turn the outside.

I'm assuming that both parts of the cap should be solidly attached, correct?

And if they're not, then that cap is defective, correct?

[53a1]

Did you try to rotate the cap and get it started at different points Shouldn't have to do this but mine only goes on starting at one particular position. May be that the neck of your tank is worn that way.

[wesk]

True, you have a defective cap. To measure B & D jsut hold the ruler perpendicular to the cap gasket and read where it meets the lower edge of one of the three locking tab/ears.

[jbjeeps]

True, you have a defective cap. To measure B & D jsut hold the ruler perpendicular to the cap gasket and read where it meets the lower edge of one of the three locking tab/ears.

Wes,

Thanks once again for your help!