Replacement Deck Fill Caps for Mk 1.5

[Dave Spencer]

I have deck fill caps as shown in the attached picture.  They aren't leaking at the moment but I'd like to take some preventative measures to replace them before they leak.  I'd also like to have a few spares in case one goes overboard.  The Catalina Direct website shows these caps are no longer available and goes on further to say:
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You must replace the entire assembly, as the caps do not have the same thread pitch or diameter (we checked). Like your old cap(s), this replacement does not require a key to open. The replacements have a flip-up opener. They are now color coded to help avoid someone putting water in your fuel tank. Choose water, waste or fuel from the links below under "May we also suggest".

Note: Every deck pipe design is of a different diameter, thread form, and thread pitch. No other cap will work with your original deck pipe. If you order any other deck pipe cap we offer it will not fit. You must replace both the cap and pipe assembly with one of the choices offered below.
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https://www.catalinadirect.com/index.cfm/product/1428_752/deck-pipe-and-cap-plastic.cfm

The PO has already replaced the pump-out deck filler assembly with a Perko (I think it's Perko brand).  Whether it's Perko or not, caps to fit it are available almost everywhere.

I certainly don't want to have to deal with a cracked or leaking fuel fill cap in the middle of a cruise.  I also would prefer not to have to replace the entire deck fill assembly for the fuel and two water tanks if it is at all avoidable.  That sounds like an ugly job.  Has anyone found a replacement cap for this style of deck fill?  Or, does anyone know what the thread specifications are?  As a last resort, I wouldn't mind making a drawing and having a machine shop make a few caps for me if I could get enough technical information.  Unfortunately, my boat is 250 km away and buried in a deep freeze at the moment so I can't get to the caps to measure them myself. 

[Stu Jackson]

Dave, are all of your other caps like the waste you pictured?  I'm dense today. 

[Dave Spencer]

Yes, all except the pump out / waste which was replaced by the PO. (The picture in the original post is from the CD website; it's not a picture of my boat). My waste deck fitting has a much more common cap that can be purchased at most marine fuel stations in my area. The one pictured is on my fuel and two water tanks and is apparently an oddball. Very attractive looking and effective so far but apparently hard to replace. Hopefully I'm wrong and the collective wisdom of the forum will point me in the right direction.

[Freedom]

Dave, I have the same caps on my 1993 Mk 1.5. Several years ago I replaced the gasket only on the cap and I have had no problems with leaking. If you are worried about the threaded female portion of the assembly leaking you could always rebel with some butyl tape.

[Dave Spencer]

Thanks Freedom,
The caps aren't showing any signs of cracking and I have no leaks at the moment. I routinely inspect and take good care of the o-ring; especially on the fuel cap. In short, I don't have an immediate problem but I will be despondent if one of the caps ever goes overboard and there is no replacement cap available forcing me to replace the whole assembly built into the deck.
Thanks for the suggestions.

[Ron Hill]

Dave : You are lucky that your caps are BLACK as that color is more UV resistant than the older colored caps!!  As mentioned keep checking the "O" ring gasket and you should be OK.

If you are concerned about the fuel, a number of us have changed out that entire fuel fill and replaced the factory fill with a Stainless fuel cap and fill (Most are stamped DIESEL) . 

Look in WiKi and Mainsheet tech notes for the "How to".  It is not that bad a job. I believe I changed mine in about 1 hour - by myself!! 

A few thoughts