Groco Ballcocks/thruhulls issue

Maine Sail · Aug 26, 2013

CYQK said:
Hey
Desided it was good logic to upgate my ballcocks to the good groco ones talked so much about.Again many thanks to Mainsail the guru
Came across an issue that perhaps could save others lots of time

Ordered the valves from my supplier and they suggested the thru hulls they had in stock
Just happened to be perko
Turns out the threads on the groco do not fit other thru hulls

Sooooooooooo, when you update your balls make sure they are AC not DC

PROTECT YOUR BALLS

Gary

They should all be industry standard threads on the thru-hulls (except Marelon). Every 1" thru-hull should fit every 1" seacock....

Course if you are fitting a ball valve to a thru-hull fitting this is going to be a thread mismatch NPT vs. NPS..... A true seacock uses NPS threads as does a thru-hull fitting..

Send us some pics. My guess is you were sent the wrong size thru-hull or the end of one may have some damaged threads.

twalker H260 · Aug 26, 2013

I had a similar issue - I was replacing ball valves and wanted to leave thruhulls in place and use groco flanged adapters as recommended on Maines site. - ball valve would thread onto existing thruhulls and adapter, adapter fit on thruhulls before cutting the thruhulls to length. After cutting thruhull to appropriate length the adapter would no longer go on.
Eventually tried a thruhull at my supplier - (Cargo East) and it fit just fine. - turns out the original thruhull was designed for use with either straight pipe or tapered but when the inboard portion was cut down for length to use with the adapter the remaining threads were very slightly oversize and would only allow the adapter to turn on about 1-1 1/2 threads.

Could be same issue with the perko. Originals on my boat were marine hardware inc.

My new thruhulls are Buck Algonquin.

Maine Sail · Aug 27, 2013

CYQK said:
Mainsail
It is with the most of most of respect that i have to disagree
My logic was exactly the same as yours which was why this issue was so difficult to resolve
Should be able to take any thru hull and thread it into any ballcock right?

Thought so untill I talked to Patrick at Groco
Turns out Groco has a slightly differant thread check it out for yourself and see
Was an dincredibly annoying problem toolk lots to figure this one

Love Groco products but when their thru hulls arrived they were more expensive and the casting were awful looked like the brooks range in side had to spend a long time grinding the interior smooth

Just sayin
Gary

The fact is that Groco uses the standard US NPS/NPT threads all manufacturers use. I have worked closely with Patrick over the years and just got off the phone with him to confirm there are no issues going on.

What you likely had was a thread tolerance mis-match between brands. The machines are supposed to be maintained to remain within the specs from the Machinists Handbook and defined by the ANSI/ASME standards for US pipe threads. Unfortunately they do not always maintain machines as often as they should and cutting heads & die wear occurs.

Because these are all bronze castings that are then machined they can look "slaggy" on the parts that are not machined.

Groco uses standard US ANSI/ASME compliant NPT/NPS tappings, as does everyone else left making bronze seacocks and thru-hull fittings with the exception of Marelon, on some pieces.

Conbraco/Apollo, Spartan, Buck Algonquin, Groco, Marine Hardware, Perko etc. etc. all use US standard NPS/NPT threads in their seacocks and thru-hulls. This does not mean you can't get a thread tolerance issue when dies wear between manufacturers. It happens in the plumbing trade all the time....

The ONLY different thread that Groco has is called a "combination thread". This is still an NPS thread but they shave the peaks of the first few threads of a thru-hull off to get more insert depth into an in-line ball valve. If you cut off the combination thread portion you still have a standard ANSI/ASME US NPS thread. Bear in mind that NPS and NPT are not meant to go together below water.....

This is a Groco "combination thread" NPS thru-hull....

And this is why you are not supposed to thread NPS to NPT...... NPS to NPT on left, NPT to NPT on right.

What exactly were you trying to thread together?

Was this an in-line ball valve and a thru-hull? = NPT to NPS

Was it a flanged proper seacock and a thru-hull fitting? = NPS to NPS

Maine Sail · Aug 27, 2013

CYQK said:
Mainsail
Bought the BVseries ballcocks 750 1000 1250 came from paynes marine supply in toronto

When complaing to them they acknowledged the issue and offered a refund on the perko ones
Groco thru hulls were delivered today tried them and they go on just fine

Your post is about as technical as anyone could ask for THANKS!!!!!!!!
Guess I got an oddball as always I like to add stuff to help others
Gary

Sounds like Perko let their machines get a little out of spec. Other than Spartan tapered cone seacocks the Groco BV series are about the best you can get....

jibes138 · Sep 21, 2013

You can measure the threads pretty easily if you can find three pieces of wire the right diameter and a micrometer. A machinist handbook will provide the correct measurement over wires or you can calculate it yourself using a little trigonometry. Find out the pitch diameter and what wire size will be tangent at the pitch diameter in a 60 degree thread. If the pitch diameter is correct the other error could be the pitch of the thread. This is the distance the thread moves in one rotation or the distance from the peak of one thread to the peak of the next. In the old days lathes has certain gear ratios that gave the threads per inch but with modern CNC equipment you can program in any number you want so it could be a programming error. Most male threads are measured using ring gages that are high and low limit (go or no-go). In the absence of ring gages it is quite easy to measure over wires to get an exacting measurement of the actual thread size. All this information on thread size and tolerance and measurement over wires should be readily available on the net with a search.