Need Gas Cap for 19.5 ft. Sea Nymph Great Lakes Special 1989

[buckboardjr]

After googling it, I couldn't fine much help. Stores having them don't give much for dimensions or thread pitches. My thread size using inside calipers down in the bore are 1.75 in. to tops of threads so if the threads are 1/8 in. deep, I think my cap's threads would be 2 in. maybe 1 7/8. Any suggestions would be appreciated. Thank

Edited July 7, 2021 by buckboardjr

[Sean Youngblood]

My 1990 has no threads just a flip up cap.

[buckboardjr]

Yours looks like it's up on the gunnel. Mine is in the rear splash pan. Thanks for your input

 

 

[Sean Youngblood]

Yes mine is on the port side gunnel

[Crayfish]

I thought I might have one for you, but I must have thrown it out.  I replaced the fuel fill line and fitting / cap last year on my 1983 191CC.  Thought I might have held onto the cap but I can't find it.  I would try a cap for any other 1.5" fuel fill and see.  The threads could very well be the same.

 

Good luck!

[buckboardjr]

Thanks for checking. 

[keepin it reel]

hi  bucknoard i may have a idea for a temporary fix home depot or lowes in the plumbing department carry whats called a test plug they are an expandable rubber based plug with a wing nut in the center the more you tighten the wing nut the rubber expands they also come in various sizes maybe something to check until you find a replacement 

[buckboardjr]

Thanks Keepin it Reel. Well after 3 trips to town/ marinas/ hardware stores, and more precise measuring, and calling Perko, and Marine shop on web, I measured it out to have tapered threads 1.70 down deep and 1.95 at the top with 12 threads per inch using a thread pitch gauge. Come to find out 1 1/2 NPT dimensions are that. So I did a search for 1.5 in. NPT plug with Oring and boom came up with this. Thanks all for looking. None of Perkos's matched up. Went to Johnsons pools and spa and they had them.

[keepin it reel]

good to know as i have the same boat and hopefully i wont lose my fuel cap but if i do i know what to do thanks

[buckboardjr]

Keeping it Reel. Is yours in the splash well? No hurry, but if you get the time and can post a few pics of the cap, I'd like to see it. And if you have calipers and can verify that the threads are tapered I'd really like to know for sure. Also is there an O-ring at the base of the threads that seals in the tapered edge of the bung. I ask because my research of Seachoice and Seadog  filler necks showed that they use NPSM threads which stands for National pipe straight mechanical threads and though I gauged my threads as being tapered maybe it is because it is a short amount of threads and even straight threads may gauge as tapered because of so few threads. Thanks

[keepin it reel]

yes i can get some pictures of mine and yes it is in the splashwell its in storage at the moment as i purchased a grady white seafarer 22 so its waiting to get its chance to get back in the water lol ill be in touch

[mr 580]

I’ve found boat parts at “great lakes skipper.com” - might be just as easy to replace complete fuel filler neck w/new cap vs trying to find a cap.  Not worth the risk getting water in the tank.

[buckboardjr]

9 hours ago, mr 580 said:

I’ve found boat parts at “great lakes skipper.com” - might be just as easy to replace complete fuel filler neck w/new cap vs trying to find a cap.  Not worth the risk getting water in the tank.

Thanks. Whole filler neck doesn't have access. Would require deriveting structure