Leaky bungs

[Old Scaley]

A couple of years ago I noticed that the tinnie was taking on a bit of water. Nothing too serious but enough to run the bilge pump from time to time. I suspected the bung assembly a d decided to try new bungs. Went to Whitworths but they didn’t have the same size and thread so I bought new housing and bungs. When I got to installing them, they wouldn’t fit because of the configuration of the strokes, somI decided to look for the right size bungs and reinstall the old housing. Found some after looking for a while and all was good for a while.

Recently the same slow leak has occurred and last week I put some marine silicon around the housing. Same problem happened last time I was out so I filed the hull with water today to test my assumption that it was the bungs that were the problem, and sure enough, it was. 

So, my question is should I drill out the rivets, put more silicon on the plastic housing and rivet it up again; or is there a better product than silicon that I can use to seal up the area? Or should I just keep running the bilge pump from time to time? And yes, I have tried new bungs.  

[Andrew_P]

Are you using the white sikaflex steve?

[Old Scaley]

33 minutes ago, Andrew_P said:

Are you using the white sikaflex steve?

I did originally but latest effort was a clear marine silicone sealant. 

[Bretto77]

Marine sikaflex. But clean everything very well. Edges of all penetrations with scotch Brite (or if necessary fine emry) back to shinny. Then with brake clean before applying sealant.

[Bretto77]

1 minute ago, Bretto77 said:

Marine sikaflex. But clean everything very well. Edges of all penetrations with scotch Brite (or if necessary fine emry) back to shinny. Then with brake clean before applying sealant.

Yes I would remove and clean the whole lot before starting again. 

[Bretto77]

Sealant in all penetrations before popping new rivets.

[Bretto77]

I assume you are using blind ally and not stainless rivets?

[Old Scaley]

2 minutes ago, Bretto77 said:

I assume you are using blind ally and not stainless rivets?

Yes @Bretto77.  Thanks for your input.

[Bretto77]

Having said all that however I had a bit of an issue in @Kat's boat at one point and thought I was going to have to re-fit the bungs. Closer inspection revealed a slightly twisted bung washer and slightly gritty thread. Sorted that and no dramas... Touch wood...

[mangajack]

Pop rivets generally have a zinc plated or cadmium plated pin in them which breaks off when the rivet is set. This small piece of steel starts galvanic corrosion inside the rivet when exposed to salt water.

Best to use Gr316 stainless screws, nuts and washers rather than pop rivets.

The use of Duralac is highly advised when different metals come into contact as well.

Check your sealant is neutral cure, quite a lot of silicones are acid cure.

Most polyurethane sealants are neutral cure.

[Junky]

Fixtech fix 190. 

I'd replace the lot Steve and also use blind aluminium rivets. 

I think the centre pull is titanium. 

I have some if you want some. 

 

That'll stop you spending another six months in a leaky boat, lucky just to keep afloat. 

 

[Angry51]

19 hours ago, mangajack said:

Pop rivets generally have a zinc plated or cadmium plated pin in them which breaks off when the rivet is set. This small piece of steel starts galvanic corrosion inside the rivet when exposed to salt water.

Best to use Gr316 stainless screws, nuts and washers rather than pop rivets.

The use of Duralac is highly advised when different metals come into contact as well.

Check your sealant is neutral cure, quite a lot of silicones are acid cure.

Most polyurethane sealants are neutral cure.

My choice is stainless bolts and locnuts as manga says.

That's all I ever use, not into rivets.

[Old Scaley]

Ok, so fixed now (sort of). Stripped the old fittings out. Looked in ok condition but a little rough around the threads. Probably cross threaded a few too many times. Removed all the old silicon and took everything back to a nice shiny aluminium surface. No evidence of any corrosion or changes in the metal. This time Whitworths did have the exact same thing so bought two more and a fresh tube of marine sika. Refitted with lots of sika and blind aluminium rivets on the public holiday while you lot were out scaring the fish. 

Left it to cure until this arvo (48 hours). Put the bungs in, filled hull with water and what do you know - still leaking. Managed to work out that it was leaking from the thread. Removed and replaced the bungs a few times, taking care that they weren’t cross threaded and the washers were sitting flat. Same result. Put some plumbers tape on the threads and that improved it a lot but still a drip from both units. Tried screwing the bungs in from the inside and hey presto, nice and dry. So no more leaky bungs but a bit frustrating. I will keep fiddling but in the meantime I can go out now absolutely confident the hull is not leaking.

Thanks everyone for your input.

[Kat]

Hi Steve -so I know I am only a girl who has worked in an office most of her life (leave all those tool things to the men in my life ) - but sounds to me like the bungs themselves are defective (not fit for purpose) - or am I misunderstanding your post?

[Old Scaley]

26 minutes ago, Kat said:

Hi Steve -so I know I am only a girl who has worked in an office most of her life (leave all those tool things to the men in my life ) - but sounds to me like the bungs themselves are defective (not fit for purpose) - or am I misunderstanding your post?

Hi Kat. Now, dearie, let me mansplain it for you. You are 100% correct. The bungs are a coarse thread and don’t seem to be the best manufactured piece of kit around. But to replace them with another type would be problematic and so I am happy to have a workaround that means any passengers I have on the boat can stop looking at me nervously when I turn on the bilge pump on a calm day and water streams from the outlet. BTW, I would never actually call anyone dearie. 

[Angry51]

3 minutes ago, Old Scaley said:

 BTW, I would never actually call anyone dearie. 

You would if the bilge pump didn't work