M-5 Gas Cap

[WitchesBoyToy]

Looking to get a couple replacement gas caps for an M-5. Other than calling Maule is there another place to get these? Anybody got a link?

[Andy Young]

Gas caps are a somewhat universal part number 10640, available from Carquest, Stant, and others. These can be bought at most auto parts stores.

On many Maules, you will need to machine (or grind or file) down the flange of the cap some to clear the screws that hold the trim ring on the wing skin. If you buy the caps from Maule, the Stant 10640 is what you will get, but they will have already done the machining of the flange for you.

Just recently I noticed that some vendors are now selling caps under that number that are a newer style, which will not work. Make sure you’re getting the ones that are all metal (not a plastic top) and have the flat tab sticking up on top to turn them (not just a smooth, slightly-domed round cap).

[VA Maule]

You can also tell the auto parts counter guy you need the behind the license plate gas cap for a 1974 or earlier Ford car

[AndrewK]

Timely post, I could use some new cap gaskets so now I know what to look for.

[Andy Young]

Often when I need new cap gaskets, I just buy new caps at the auto parts store, take the gaskets off them, and put them on my old caps. Saves machining the new caps every time.

[andy]

I put Parker O-Lube on my gaskets every few flights to keep them from tearing or wearing out. If they do, then I buy new Stant caps and take off the gaskets. i'm still looking for a Stant part number for the gaskets alone. Does anyone have it?

[BDJ238]

Gas caps are a somewhat universal part number 10640, available from Carquest, Stant, and others. These can be bought at most auto parts stores.

On many Maules, you will need to machine (or grind or file) down the flange of the cap some to clear the screws that hold the trim ring on the wing skin. If you buy the caps from Maule, the Stant 10640 is what you will get, but they will have already done the machining of the flange for you.

Just recently I noticed that some vendors are now selling caps under that number that are a newer style, which will not work. Make sure you’re getting the ones that are all metal (not a plastic top) and have the flat tab sticking up on top to turn them (not just a smooth, slightly-domed round cap).

I ordered these recently from O'Reilly's and can confirm they need to be trimmed. If anyone has ab part number for ones that do not need trying that'd be great. If not I'll probably just pull the o-rings and call it good.

[DavZeeMXT]

Anyone who’s owned a Maule for a length of time has had this problem. I’ve purchased them from Maule directly and they’re expensive especially comparing them to getting them from an auto parts store. It’s always been the gasket, not the cap itself wearing out. Auto store caps definitely need to be trimmed and this might be why they cost more from Maule. It’s easy enough to do on a bench sander or grinder. I’ve not been able to just replace the gasket because it seems to be pinched between the parts of the cap when it’s made. Lately I’ve been trying Andy’s suggestion and using Parker O Lube on the gasket. That stuff can be pricey but if you shop around it can be had reasonably. Seems to be working pretty good so far. I’ve been putting it on the tank flange and then putting on the cap so it’s on the right place of the gasket. A dab will do ya. Thanks Andy!

[Hinterland]

I have had good experience with surplus Cessna gas caps. They are typically the same price as anything you will source from NAPA Auto, but they are vented and won't syphon your fuel on a hot day.

[VA Maule]

Caps need to be non-vented!!! A vented cap on top of the wing ( low pressure area ) has the potential to draw out fuel during flight . That’s why fuel tank vents are open to the high pressure area under the wing.

[Kirk]

Caps need to be non-vented!!! A vented cap on top of the wing ( low pressure area ) has the potential to draw out fuel during flight . That’s why fuel tank vents are open to the high pressure area under the wing.

I don’t believe that is correct. The Stant 10640 cap that Maule uses is vented, non-surge. Years ago, someone (Jeremy?) wrote an explanation of the system. My recollection is that the vent lines allow expanding air to release and vented caps allow air to enter.

It’s been a few years since I ordered caps or gaskets from Maule, but I don’t remember it being that bad. I did find the Stant 10640 caps for as low as $4 online and that would be a good price just for the gaskets. Personally, I can’t get thrilled about taking a grinder to the caps or somehow get it chucked in something to turn it down.

The gaskets are hard to coax off the caps, but can be removed by stretching, warming the material with your fingers. I have had to use some needle nose pliers to pull it past the locking tab and managed to do so without cutting or tearing it.

I keep a spare cap (from Maule) in my onboard toolkit just in case I lose one while out on a trip.

Kirk

[andy]

My Stant fuel caps that I bought from Maule are stamped "Vented" and "Anti-Surge". Here's a photo of the 10640:

https://www.rockauto.com/info/153/10640.jpg

[Kirk]

My Stant fuel caps that I bought from Maule are stamped "Vented" and "Anti-Surge". Here's a photo of the 10640:

https://www.rockauto.com/info/153/10640.jpg

Yep that’s the one. A lot of the caps on the market now seem to be 10640 “equivalent “ with plastic parts. I’d stay away from those.

Can anyone describe how you can machine those caps to the required thickness? I just can’t see filing or grinding giving very neat or accurate results. Then there’s the problem of fishing out all the filings…

Kirk

[PCH]

Just bought 4 new gas caps from Maule because the rubber gaskets were on their last legs. I would have just replaced the gaskets but couldn't find the right size/thickness.

Turns out the new Maule caps are really tight-almost too tight. Will the Parker O Lube help?

I'd also love to know if the correct gas cap gaskets exist out there.

Also, Maule has two types of gas caps, long neck and short neck. I think the short neck caps are for planes before 1992.

[onfinal]

I'd also love to know if the correct gas cap gaskets exist out there.

I could not find an 'off the shelf' product.

I use NBR BS2751:BA60
It is a Nitrile Butadiene Rubber to British Standard 2751, with a Shore A hardness of 60 degrees
This British Standard meets the required resistance to organic liquids, i.e. petroleum based fuels for gaskets and seals
I had a dozen 'washers' stamped/punched from 1.5mm, 2mm and 3mm thickness sheet, my fuel caps vary in fit.
OD = 60mm and ID = 35mm. Thirty six 'washers' cost £30.
The old washers were removed with ease and the new washers stretch sufficiently to pass over the tabs.
With a dozen of each thickness I am OK for a few years