Brass to cast iron

[Bullet2012]

i need to seal a threaded brass plug into a cast iron manifold. The thread is 3/8 npt but due to corrosion the female thread in the cast has all but disappeared.
the manifold is part of the exhaust on a boat, it is water cooled, the water is not high pressure but has a fairly large flow.
I have a few choices.
1) replace manifold, could get very expensive.
2) make a permanent joint between the brass plug and the manifold

so option 2 is my preferred method, but how can I join/ seal them.
can I solder them ?
or will a chemical metal style be better ?

yes this has to be one on a budget without removing the manifold.
not worried about draining for winter as another method is available.

 

[selectedgrub]

Nickel plated plug?

 

[Bullet2012]

Do you mean do I have a nickel plated plug ? If so , the answer is no, only brass.

 

[selectedgrub]

OK you can buy black steel hex plugs.
Sorry I don't know too much about galvanic corrosion

 

[Bullet2012]

Nope only got brass.

 

[jerrytug]

Personally, I would use some chemical metal stuff, and follow the instructions about mixing and degreasing properly.

 

[Bullet2012]

Personally, I would use some chemical metal stuff, and follow the instructions about mixing and degreasing properly.

Thanks, I know you understand the use and environment

 

[Kram]

You have quite a few options I think,

Tap it next sensible metric size up and new plug.

Ream the hole and a light press fit plug.

If the manifold is watercooled then the max temperature will not be too high for a braze/silver solder joint, if your able to heat it to 650c.

I wouldnt trust epoxies under water or above 100c for anything important

 

[Bullet2012]

If the manifold is watercooled then the max temperature will not be too high for a braze/silver solder joint, if your able to heat it to 650c.

No, I have no equipment to obtain that sort of heat and the environment the engine is enclosed in would definitely not survive that sort of temperature. Definitely below 100c though probably around 65-70 max unless another failure occurs

 

[Wildefalcon]

Loctite 660?

 

[Agroshield]

Chemical metal would do. Strap over the plug held by self-tappers would stop a flood in case of failure. Tie an oak plug, whittled to the approximate hole diameter somewhere nearby.

Helicoil the NPT thread (for example, just to show they do exist: http://www.knighton-tools.co.uk/acatalog/NPT_THR.html) and use a proper thread sealer.

What are the consequences if it weeps a little? What are the consequences if it falls out? Is is easy to give it a regular visual examination once in a while? The answers to these will dictate the best repair method.

 

[piman]

Hello Bullet,

I agree with Kram and suggest the best solution is to re tap to a larger size or alternatively use a helicoil repair to keep it 3/8" NPT.

Alec

 

[Agroshield]

...best solution is to re tap to a larger size...

You are fortunate in this case as 3/8-18 NPT is 0.675" (17.1mm) OD. When tapping into a thin casting, it is best to maintain a comparable thread pitch, so standard metric coarse will not work here.

However, M20 x 1.5, with a tap drill of 18.5mm is standard for electrical conduit and Mr Screwfix will sell you some nice metal stoppers with this thread (https://www.screwfix.com/p/deta-hex-plugs-20mm/1367J).

 

[Bullet2012]

No room to drill or even get a tap in

 

[Bullet2012]

Why has this been moved ?

 

[zx9]

You are fortunate in this case as 3/8-18 NPT is 0.675" (17.1mm) OD. When tapping into a thin casting, it is best to maintain a comparable thread pitch, so standard metric coarse will not work here.

However, M20 x 1.5, with a tap drill of 18.5mm is standard for electrical conduit and Mr Screwfix will sell you some nice metal stoppers with this thread (https://www.screwfix.com/p/deta-hex-plugs-20mm/1367J).

This or I had time / speed certs done on my (aluminium) Gpz1100 brake castings which were fluid tight for years.

No room to drill or even get a tap in

It would need to come off to replace the manifold so no different to removing for repair?

 

[zzr1200]

Use this....

Bearingboys

Online

www.bearingboys.co.uk

 

[mike os]

The corrrect way would be to retap, or thread repair,

If that's not an option you are not going to be able to retap epoxy putty either, so not sure that is an option

So only choice is what flavour of locktite..... which wil depend on the pressure in the manifold and how much thread is left

If its properly stripped it probably won't stay in with just locktite

Soft solder would do if temperature is low.... but heating the manifold in place will be difficult

 

[Kram]

No room to drill or even get a tap in

Have you got a photo of the surroundings?

I have modified drills and taps before for tight access. A short stub straight flute drill might be possible turned by hand.

Another option then, soft lead oversize plug and peen it into the hole.

 

[grim_d]

Helicoil and thread sealant. Job jobbied.

No room? Make room. or find someone with a 90 degree drill.