Help - Stripped Thread

[LONG_KEELER]

Was splashed last Monday after summer lift out. Blakes 1 1/2" seacock leaking badly back out again on the hard Tuesday. Booked to go back in Monday 22nd June.

Seacock came out of the hull fairly easily and there was very little sealant.

Was bedding in the Blakes seacock and one of the four studs which take the seacock body stripped. I was only nipping up gently too.

The studs are bronze and look like they have been glassed in to the hull from the outside without a backing plate.

The studs are counter sunk into the hull. I do not think that the studs were the cause of the leak.

What to do ? I could try extra washers but there is not lots of thread. The studs are 5/16 ".
Is it possible to tap a new thread into bronze ? If so, could I make a metric thread and what size should it be ? Perhaps I could add chemical metal and cut a new thread ?

Can I stop nipping up the nuts when the sealant starts to ooze ? If so, I might get away with adding washers.

Any ideas greatly received.

 

[steve66]

If its bronze its fairly soft....try metric stainless nuts to try to cut a thread
5/16 is around 7.9mm......you may get away with an m7 nut

 

[Rappey]

You can still buy the proper bolts and nuts but they are very expensive . I bought 4 from the local chandlery!
It's possible that stainless is not that far from bronze from what ive seen online but I would strongly suggest you take professional advice before considering it .
If there is a nuts length of thread left I would go the washer route ?
With 3 good bolts and an adhesive sealant like sikaflex I can't see the 4th bolt being a seriously weak point.

 

[andsarkit]

Blakes seacocks are usually fitted with countersunk bronze screws with nuts on the inside. Alternatively with a coach bolt and a reinforcing ring on the outside. Why not drill out the old screw and replace with new. The original was probably whitworth but UNC is close apart from a slightly different thread angle.
Available here bronze bolts
Not sure why you want to cut a new thread as this would be a lot weaker. Are you sure the other threads are not also suspect?

 

[Iliade]

Are the studs pink? If so ditch them.

If not you could die the stud with any thread you felt like that would provide a grip for the matching bronze nut you found lying about. (No chance of that in reality sadly)

If you are using a polysulphide sealant (e.g. Sikaflex) you nip until the sealant just thinks about oozing . Then when it has set, you nip a little more. Washers may well work for you the studs are not preferentially corroded. (pink)

 

[Iliade]

Blakes are a little chary about exactly which bronze their bolts are made from. I would strongly recommend that you do not stray far from their point in the galvanic scale.

Bolt 3/8" x 2"

 

[Rappey]

Available here bronze bolts

£3.50 for dzr. Phosphor bronze are £21

Just seen post above, £8 sounds better from blakes lavac.

 

[LONG_KEELER]

Thanks chaps, all good.

Classic Marine is down the road from me. I actually purchased 8 nuts from them this week. Only £5.92 the lot. On a previous boat , I purchased
silicone bronze studs and nuts which were pricey but worth it I think.

Drilling out one of the studs is probably beyond my ability . On the plus side, if comes to it , I suppose the material is soft . Do I use an HSS drill bit and apply pressure but slowish speed ?

 

[Rappey]

A guy on ebay is claiming to be selling genuine blakes phosphor bronze bolts at £21 but as lliade points out, hard to know what bronze the real ones really are.