Silencer replacement - conventions

[cheesegas]

Hi all. Replacing the silencer on my boat as it's got an ever widening rust hole at the bottom at the weld of the bracket, presumably where the condensate collects. It's a hospital silencer, and as I've found a very good deal on a barely used new one of similar dimensions, I'll be replacing it almost like for like. Engine is an Isuzu with a dry exhaust and air cooled manifold, I'm going to replace the flexi hose whilst it's in bits too.

 

The new one has 2" BSP male ports, and needs about 1' of flexi hose between manifold and silencer. Manifold has 4 stud flange on it which currently has a welded 1" long stub of pipe with a male thread cut in it. I'd like to use something like the photo attached rather than the concertina stuff as it's what I've used on cars before. Haven't seen any on boats though - is there a reason?

 

What's the convention to get from flange to BSP? Weld the flexi on, or clamp it? I was thinking manifold flange to 2" pipe, weld one end of the flexi to that, weld the other end to a short stub of 2" pipe with a male thread cut in it, then join it to the silencer with a female-female coupler. The other end would just be plain BSP 2" pipe to the skin fitting.

 

I'm going to fabricate a cradle for the new silencer to be clamped to with big Jubilee clips as I don't like welding brackets on big heavy thin walled things which vibrate! That's how the original was mounted, and it looks like it was welded and re welded when the steel fractured around the weld.

 

Thanks!

[Tracy D'arth]

Flexies for boats come with threaded ends already welded on, either male or female or one of each. Usually 1 1/2" BSP but you can get larger or reducers.

 

1 1/2" bsp is about 2" outside diameter, are you getting confused?

[Chewbacka]

Something like this-

https://www.midlandchandlers.co.uk/products/bellows-with-1-1-2-bsp-male-ports-12-length-ea-023

[alan_fincher]

6 hours ago, cheesegas said:

I'd like to use something like the photo attached rather than the concertina stuff as it's what I've used on cars before. Haven't seen any on boats though - is there a reason?

 

I'd say that style of bellows  is actually pretty common on narrow boats, (albeit wth the ends usually  being threaded, as mentioned above.

It's how ours is done.

 

[Tracy D'arth]

1 minute ago, alan_fincher said:

 

I'd say that style of bellows  is actually pretty common on narrow boats, (albeit wth the ends usually  being threaded, as mentioned above.

It's how ours is done.

 

 

 

Really? An elbow instead of a bend?

[cheesegas]

22 hours ago, Tracy D'arth said:

Flexies for boats come with threaded ends already welded on, either male or female or one of each. Usually 1 1/2" BSP but you can get larger or reducers.

 

1 1/2" bsp is about 2" outside diameter, are you getting confused?

Thanks, yep it’s 2” OD, haven’t got my hands on the new one yet so will double check when it’s delivered. Didn’t find the flexi with pre welded ends in my searching, makes things easier! As for sealing the threads, just copious amounts of copper slip?

 

 

20 hours ago, Chewbacka said:

Something like this-

https://www.midlandchandlers.co.uk/products/bellows-with-1-1-2-bsp-male-ports-12-length-ea-023

Cheers, will order one of those. 

[BEngo]

Seal the threads with oodles of copper slip, as you suggest.  If there are any unions in the run don't forget to do the union nut thread and mating face as well as the pipe threads.  That way you might one day get it apart again.

N

[ditchcrawler]

45 minutes ago, BEngo said:

Seal the threads with oodles of copper slip, as you suggest.  If there are any unions in the run don't forget to do the union nut thread and mating face as well as the pipe threads.  That way you might one day get it apart again.

N

A definite MIGHT. 24" stillies and a big hammer wouldn't move mine

[Tracy D'arth]

33 minutes ago, ditchcrawler said:

A definite MIGHT. 24" stillies and a big hammer wouldn't move mine

Gas axe shifts anything. If not, thermic lance.

[ditchcrawler]

43 minutes ago, Tracy D'arth said:

Gas axe shifts anything. If not, thermic lance.

But like a disk cutter, you cant use them again

[BEngo]

4 hours ago, ditchcrawler said:

A definite MIGHT. 24" stillies and a big hammer wouldn't move mine

Don't force it lad.  Get a bigger 'ammer, and some proper Stilsons.  For 2in BSP you need at least the 36 inch version.

 

N

[Ronaldo47]

Plus-gas, lighter fuel, or even motor spirit are highly penetrating and can help unsieze threads. However, as rust occupies a greater volume than the original iron, badly rusted joints can be the devil to unsieze. 

[ditchcrawler]

53 minutes ago, BEngo said:

Don't force it lad.  Get a bigger 'ammer, and some proper Stilsons.  For 2in BSP you need at least the 36 inch version.

 

N

Yes, but I don't own any that size also I didn't have a big fixed pipe vice to hold it still. so I had to buy a new one, it had only been undisturbed for about 15 years and well copperslipped

[cheesegas]

Yep, I’m not counting on the current exhaust to disassemble without an angle grinder…

[Tracy D'arth]

1 minute ago, cheesegas said:

Yep, I’m not counting on the current exhaust to disassemble without an angle grinder…

Use two hammers, a heavy one behind and another lighter on the other side across the female part of the fitting. Repeated blows will loosen the threads,   hopefully!

[ditchcrawler]

2 hours ago, Tracy D'arth said:

Use two hammers, a heavy one behind and another lighter on the other side across the female part of the fitting. Repeated blows will loosen the threads,   hopefully!

Tried that with what I had, but like the 24" stillies, not big enough. Only had a lump hammer and an engineers hammer. I have broken dozens of these when I worked for a living but never one off an exhaust. Standing on the stillies while some one beats it with the sledge hammer

[Chewbacka]

I used to find on old cars (many years ago) a fair bit of heat from a blow torch would break up the rust followed by some wd40 when it had cooled to a safe temperature