Replacing my exhaust and how to choose a hospital silencer?

[ditchcrawler]

16 minutes ago, ivan&alice said:

I strongly doubt that the nut is coming off, and the flange is corroded enough that I'm prepared to pay the 25 odd quid to replace it. Seems like a reasonable price for the reduction in effort.

 

Can anyone give me insight into my pipe size? @Boater Sam has got me concerned now...

 

The outside diameter of the flange (the male threaded bit) is 2". The outside diameter of the female coupling is about 2 3/8". The flexible pipes are a round 2", maybe a little over. The exhaust outlet internal diameter is just a bit more than 1 1/2" (but not sure if this is the same internal diameter in the whole system).

The link I sent you for Cranes lists the length of the socket against thread size that may help 1 1/2"  is 54 or 55 mm long and 2" is 64 or 65mm long

[Boater Sam]

19 minutes ago, ivan&alice said:

I strongly doubt that the nut is coming off, and the flange is corroded enough that I'm prepared to pay the 25 odd quid to replace it. Seems like a reasonable price for the reduction in effort.

 

Can anyone give me insight into my pipe size? @Boater Sam has got me concerned now...

 

The outside diameter of the flange (the male threaded bit) is 2". The outside diameter of the female coupling is about 2 3/8". The flexible pipes are a round 2", maybe a little over. The exhaust outlet internal diameter is just a bit more than 1 1/2" (but not sure if this is the same internal diameter in the whole system).

Those are 1 1/2" pipe and fittings. I was convinced that they would be. Using 2" pipe you will be amazed how much more room they will take up and serve absolutely no purpose over 1 1/2", and a lot more expensive.

[Slim]

3 hours ago, ivan&alice said:

Ah! Hm. Yes I am confused by pipe sizes. The male exhaust flange is around 2" outside diameter (i.e. the threaded part). The female fittings are more than 2" outside diameter - about 2 3/8".

 

I am not able to measure the internal diameter of these fittings (as they are still assembled), but the exhaust skin fitting is about 40mm internal bore, which is a little more than 1 1/2".

 

Unfortunately no, the size is not legible through the corrosion. Does this sound like 1 1/2" to you?

A very quick google of "BSP thread sizes" will explain fully how to identify sizes. I found the answer within seconds. Tried to provide link but am on tablet and I can't hack it.

[Iain_S]

9 hours ago, ivan&alice said:

(snip)

Wouldn't those same flexible mounts be useful on the boat?

 

Not really : a car exhaust is usually rigidly fixed to the engine, and vibrates with it. On a boat, the exhaust is normally fixed to the boat, with a flexible section between system and the manifold to prevent, or, at least, greatly reduce, the engine vibration being passed to the exhaust.

[jetzi]

9 hours ago, ditchcrawler said:

The link I sent you for Cranes lists the length of the socket against thread size that may help 1 1/2"  is 54 or 55 mm long and 2" is 64 or 65mm long

 

8 hours ago, Slim said:

A very quick google of "BSP thread sizes" will explain fully how to identify sizes. I found the answer within seconds. Tried to provide link but am on tablet and I can't hack it.

I'm sorry I did try to figure it out from this material but the terminology of the different parts wasn't clear to me. There is a lot to the BSP threads as they taper in order to create a tight seal. I'm not talking about the various threads, I'm trying to identify the pipe by the outside diameter which I do understand is going to be dependent on the pipe wall metal thickness.

 

In short the 1 1/2" refers to the diameter of the inside bore and with malleable iron pipework you're looking at about 1/4" thick walls, resulting in a 2" outside diameter of the pipe?

 

9 hours ago, Boater Sam said:

Those are 1 1/2" pipe and fittings. I was convinced that they would be. Using 2" pipe you will be amazed how much more room they will take up and serve absolutely no purpose over 1 1/2", and a lot more expensive.

OK thanks so much for this identification. I will have to contact TW again... they are going to think I'm a right muppet xD

 

5 hours ago, Iain_S said:

Not really : a car exhaust is usually rigidly fixed to the engine, and vibrates with it. On a boat, the exhaust is normally fixed to the boat, with a flexible section between system and the manifold to prevent, or, at least, greatly reduce, the engine vibration being passed to the exhaust.

OK so there is no benefit to damping vibration between the boat and the exhaust. That does make mounting a lot easier.

 

My current thinking is to just use 2x 500mm long metal cable ties joined together, loop them around the silencer after lagging, and use these to suspend them from holes drilled in the vertical support on the underside of the deck.

[BEngo]

The standard outside diameter of 2 in BSP thread is 2.347 in.  The standard outside diameter of 1 1/2 in BSP thread  is 1.882 inches. Male threads will be very close to these sizes.  The pipe outside diameters may be a little larger, depending on manufacturing tolerances.

 

The outside diameter of a female fitting will be larger, but there are no standards that specify this AFAIK, so you have to measure either the male thread as close as possible to the pipe end (not the free end in  case you have a taper thread),  or the OD of the pipe.

 

N

[David Mack]

3 hours ago, BEngo said:

The standard outside diameter of 2 in BSP thread is 2.347 in.  The standard outside diameter of 1 1/2 in BSP thread  is 1.882 inches. Male threads will be very close to these sizes.  The pipe outside diameters may be a little larger, depending on manufacturing tolerances.

 

The outside diameter of a female fitting will be larger, but there are no standards that specify this AFAIK, so you have to measure either the male thread as close as possible to the pipe end (not the free end in  case you have a taper thread),  or the OD of the pipe.

 

N

And the easiest way to measure the pipe diameter may be to wrap a strip of paper around the pipe and mark across the overlap, remove the paper, measure the distance between the marks and divide by pi.

 

Pipe outside diameter should be pretty close to the size defined in the standard - too large and it would not be possible to get a die onto it to cut a male thread, too small and you will lose part of the thread form.

Edited August 20, 2019 by David Mack

[Iain_S]

BSP threads come in both parallel and taper forms. Both will seal in an exhaust system, but threads on pipe are normally parallel, as are the threads on unions and sockets, so best to use parallel, which also allows for a slight length adjustment. 

[David Mack]

1 minute ago, Iain_S said:

BSP threads come in both parallel and taper forms. Both will seal in an exhaust system, but threads on pipe are normally parallel, as are the threads on unions and sockets, so best to use parallel, which also allows for a slight length adjustment. 

???

Female BSP threads are usually parallel.  Male threads on iron pipe and fittings are almost always tapered and are tightened until the male taper is tight in the female thread. Parallel male threads on iron pipe are generally only used in conjunction with a backnut where adjustment of the length may be required. Parallel male threads are also used on brass plumbing fittings where the seal is provided by a fibre or rubber washer sealing to a flange.

See also https://en.m.wikipedia.org/wiki/British_Standard_Pipe

[Iain_S]

Very often a male BSP thread on a pipe will be parallel, as it's easier to cut. Depending on wall thickness, it may be difficult to get a taper in any case. Best practice is both male and female threads either parallel or taper. Male taper into female parallel works, but male parallel into female taper is very iffy, and is a recipe for stripping threads.

[jetzi]

Thanks for the really valuable help so far everyone.

 

I've settled on the largest 1 1/2" silencer that's readily available - the 12" diameter x 32" long one. I've drawn it all up in three dimensions to make sure that I am getting all the right fittings, and hopefully I'll be able to get it all delivered in time to install it this long weekend.

 

Could I just ask for a final sense check?

 

One thing I'm not sure about is how much overlap I need to leave - for example, if I connect a 10" pipe into a 3" radius bend, I presume they will screw together at least a half inch or so, giving a final length of 12 1/2" rather than 13"? I'm hoping there will be enough wiggle room that I will be able to make it work regardless.

 

There doesn't seem to be a 10" long flex exhaust part, so I am thinking I'll just get the 12". Otherwise use a 10" stiff steel pipe.

 

Also I'm going to have to move the exhaust outlet slightly. A bit of a hassle. I'll patch it with something for now and have it welded shut the next time I get welding done.

Parts list:

 

6.3       GBP    Exhaust Flange Gasket
28.8     GBP    Exhaust Flange Bowman 1.5" BSP (male)
49.9     GBP    15" Flexible Exhaust Pipe 1.5" BSP (female to male)
15.9     GBP    Malleable Iron 90 degree long bend 1.5" BSP (female to female)
27.9     GBP    12" Flexible Exhaust Pipe 1.5" BSP (male to female)

                       OR steel pipe 10" male to male plus a union (12" a bit long)
255      GBP    Hospital Silencer 12" diameter X 32" length 1.5" BSP (male side entry to male exit)
4.3       GBP    Malleable Iron Socket 1.5" BSP (female to female)
14.2     GBP    600mm Black Medium Steel Tube 1.5" BPS (male threaded one end) (tailpipe)
46.9     GBP    30m Exhaust Lagging (titanium not fibreglass)
6.4      GBP    Copaslip 100g (to ensure the system will come apart in future)
455.6  GBP    TOTAL

 

 

[Boater Sam]

 

14 minutes ago, ivan&alice said:

Thanks for the really valuable help so far everyone.

 

I've settled on the largest 1 1/2" silencer that's readily available - the 12" diameter x 32" long one. I've drawn it all up in three dimensions to make sure that I am getting all the right fittings, and hopefully I'll be able to get it all delivered in time to install it this long weekend.

 

Could I just ask for a final sense check?

 

One thing I'm not sure about is how much overlap I need to leave - for example, if I connect a 10" pipe into a 3" radius bend, I presume they will screw together at least a half inch or so, giving a final length of 12 1/2" rather than 13"? I'm hoping there will be enough wiggle room that I will be able to make it work regardless.

 

There doesn't seem to be a 10" long flex exhaust part, so I am thinking I'll just get the 12". Otherwise use a 10" stiff steel pipe.

 

Also I'm going to have to move the exhaust outlet slightly. A bit of a hassle. I'll patch it with something for now and have it welded shut the next time I get welding done.

Parts list:

 

6.3       GBP    Exhaust Flange Gasket
28.8     GBP    Exhaust Flange Bowman 1.5" BSP (male)
49.9     GBP    15" Flexible Exhaust Pipe 1.5" BSP (female to male)
15.9     GBP    Malleable Iron 90 degree long bend 1.5" BSP (female to female)
27.9     GBP    12" Flexible Exhaust Pipe 1.5" BSP (male to female)

                       OR steel pipe 10" male to male plus a union (12" a bit long)
255      GBP    Hospital Silencer 12" diameter X 32" length 1.5" BSP (male side entry to male exit)
4.3       GBP    Malleable Iron Socket 1.5" BSP (female to female)
14.2     GBP    600mm Black Medium Steel Tube 1.5" BPS (male threaded one end) (tailpipe)
46.9     GBP    30m Exhaust Lagging (titanium not fibreglass)
6.4      GBP    Copaslip 100g (to ensure the system will come apart in future)
455.6  GBP    TOTAL

 

 

You need a union somewhere else you will have to cut it all apart to get the engine of gearbox out one day. Just think how you would have to rotate the silencer to unscrew it.

[BEngo]

You need a union somewhere between the flex pipe and the silencer and I would fit another between the silencer and the tailpipe. The first is essential to assembling it all.  The other will make it possible to remove just the silencer.

 

Forcing a 12 inch flexible pipe into a 10 inch space might be possible, but it won't last long, and in your proposal I would expect the flange to be the failure point  aftet a very short time.

 

N

[jetzi]

4 minutes ago, Boater Sam said:

You need a union somewhere else you will have to cut it all apart to get the engine of gearbox out one day. Just think how you would have to rotate the silencer to unscrew it.

 

1 minute ago, BEngo said:

You need a union somewhere between the flex pipe and the silencer and I would fit another between the silencer and the tailpipe. The first is essential to assembling it all.  The other will make it possible to remove just the silencer.

I was avoiding unions by selecting female-to-male flex pipes.

 

Would it be preferable to only use male-to-male pipes connected by unions? Is it OK to use a F/F bend here to save on two unions?

Note that I do use a union for connecting the tailpipe (called a "socket" in my parts list but we've been over this, and I'll get a union). This union was not shown on the diagram.

 

2 minutes ago, BEngo said:

Forcing a 12 inch flexible pipe into a 10 inch space might be possible, but it won't last long, and in your proposal I would expect the flange to be the failure point  aftet a very short time.

Alright - let me use a 10" solid steel pipe here instead of flex. I still have the flex between the engine and the bend to cut down vibrations.

 

I'm mostly concerned that a 10" overall length doesn't provide overlap to take into account the threads. Would I not need a 12" pipe to allow an inch of overlap to thread the parts together?

 

 

Here's an updated diagram showing your suggestions and the unions.

 

[ditchcrawler]

13 minutes ago, ivan&alice said:

 

I was avoiding unions by selecting female-to-male flex pipes.

 

Would it be preferable to only use male-to-male pipes connected by unions? Is it OK to use a F/F bend here to save on two unions?

Note that I do use a union for connecting the tailpipe (called a "socket" in my parts list but we've been over this, and I'll get a union). This union was not shown on the diagram.

 

Alright - let me use a 10" solid steel pipe here instead of flex. I still have the flex between the engine and the bend to cut down vibrations.

 

I'm mostly concerned that a 10" overall length doesn't provide overlap to take into account the threads. Would I not need a 12" pipe to allow an inch of overlap to thread the parts together?

 

 

Here's an updated diagram showing your suggestions and the unions.

 

Have you got any of these in there 

[jetzi]

1 minute ago, ditchcrawler said:

Have you got any of these in there 

Are those unions? If so, yes, there are three labelled on the diagram. One joining the gasket to the flex pipe and one either side of the silencer. I am however using a F/F bend, to avoid needing unions there too.

[David Mack]

How are you suporting the silencer? And also the bend at the bottom of the vertical pipe will need support.

What is the hull outlet and how is it attached to the exhaust pipe?

 

Why do you need a union between the flexible and the engine flange? If you wish to remove the section of exhaust between the silencer and engine all you need to do is undo the union at the silencer end and unbolt the exhaust flange at the other.

[jetzi]

8 hours ago, David Mack said:

How are you suporting the silencer? And also the bend at the bottom of the vertical pipe will need support.

What is the hull outlet and how is it attached to the exhaust pipe?

 

Why do you need a union between the flexible and the engine flange? If you wish to remove the section of exhaust between the silencer and engine all you need to do is undo the union at the silencer end and unbolt the exhaust flange at the other.

My current silencer is supported only by the fittings and the bulkhead it passes through.

 

The new one will also be supported by the bulkhead, and I can also put a prop under it on the floor of the aft compartment. The fore end I plan to suspend from the underside of the deck with stout metal cable ties (there is a vertical angle iron support I can drill through).

 

The bend is a bit more tricky to do without welding. The current one has a welded flat bar. I plan to cut the existing bend off and extend the support by bolting a piece of flat. Then the lagging will hopefully hold the pipe to it.

 

The genuine Beta engine exhaust flange and flex hose are both male. So I need the F/F union to be able to connect the two.

Edited August 21, 2019 by ivan&alice

[David Mack]

29 minutes ago, ivan&alice said:

 

The genuine Beta engine exhaust flange is male and the flex hose is female. So I need the F/F union to be able to connect the two.

 

So why not screw the male flange into the female flexible? A union is only needed if you want to be able to separate the joint later without rotating the pipework one side - you can unbolt the flange to achieve that.

[jetzi]

1 hour ago, David Mack said:

So why not screw the male flange into the female flexible? A union is only needed if you want to be able to separate the joint later without rotating the pipework one side - you can unbolt the flange to achieve that.

Thanks for clarifying. Sorry - I made a mistake in the previous post. The flexibles have male ends - TW Marine does not stock M/F flexibles. But if I buy elsewhere I can do this.

Edited August 21, 2019 by ivan&alice

[David Mack]

8 minutes ago, ivan&alice said:

Thanks for clarifying. Sorry - I made a mistake in the previous post. The flexibles have male ends - TW Marine does not stock M/F flexibles. But if I buy elsewhere I can do this.

A simple socket then.

[jetzi]

4 minutes ago, David Mack said:

A simple socket then.

For the sake of a couple of quid, it seems to me that it would be better to not have to rotate the flange to get the pipework apart. Also since the joints have a tendency to seize, perhaps having multiple places that it can come apart could be a good thing?

[BEngo]

 The idea of  supporting the silencer off the bulkhead is not really a great one.  There will be chafing between the two where ideally there would be a small gap.  If the bulkhead is steel it will wear the silencer away and if it is timber it will get hot and char, which is a BSS fail these days, I think.   If you have a gap it can be filled with fire rated foam, from Screwfix or Toolstation.  Ideally you want to support the silender  both sides.  Your idea of steel  cable ties is OK but you may find builders galvanised strapping is even better.  It is a 20mm wide strip of galvanised steel with holes at about 25mm intervals.  Buy it from Travis Perkins or similar.  Much cheaper than cable ties too.  A prop off the counter will be fine, but really needs to be welded to the counter and then clipped to the silencer.

 

Normally when plumbing an exhaust  length adjustments are done by cutting steel pipe to size and threading it so as to fit.  Al, the joints can then be bowsed up so they are exhaust tight.  If there is any slackness anywhere the engine 'ole eventually goes black all over.  DAMHIKT. 

 

You have two places where the pipe length needs to be 'Right'  The vertical pipe from the bend, and the pipe out the back.

 

For the vertical:  If you don't have a threading machine then cut a barrel nipple in half and screw half into the union and half into the bend.  Measure the gap and cut a bit of steel pipe to fit.  Unscrew the nipples and  tack the nipples to the pipe.  Refit and check, Remove and  Finish weld.  I know your welding is beginner level but you should be able to hack the tacks.  Have you a mate that caould finish them?

 

Similarly for the back pipe , but it can be welded to the hull later, if you leave 3-4 in sticking out.

 

N

[jetzi]

10 minutes ago, BEngo said:

 The idea of  supporting the silencer off the bulkhead is not really a great one.  There will be chafing between the two where ideally there would be a small gap.  If the bulkhead is steel it will wear the silencer away and if it is timber it will get hot and char, which is a BSS fail these days, I think.   If you have a gap it can be filled with fire rated foam, from Screwfix or Toolstation.  Ideally you want to support the silender  both sides.  Your idea of steel  cable ties is OK but you may find builders galvanised strapping is even better.  It is a 20mm wide strip of galvanised steel with holes at about 25mm intervals.  Buy it from Travis Perkins or similar.  Much cheaper than cable ties too.  A prop off the counter will be fine, but really needs to be welded to the counter and then clipped to the silencer.

Indeed the bulkhead is also in the middle which is not really where you want the support. I planned to lag the silencer before inserting it into the hole, which should protect somewhat against the chafing. I'll make sure it is supported at both ends. The bulkhead is steel, and is supporting the current (much smaller) silencer.

 

The prop on the counter should be OK without welding, but I'll see if I can bolt it into something, and perhaps use strapping to connect it firmly to the silencer.

 

Thanks for the galvanised strapping tip. I'll use this rather than cable ties.

 

20 minutes ago, BEngo said:

Normally when plumbing an exhaust  length adjustments are done by cutting steel pipe to size and threading it so as to fit.  Al, the joints can then be bowsed up so they are exhaust tight.  If there is any slackness anywhere the engine 'ole eventually goes black all over.  DAMHIKT. 

 

You have two places where the pipe length needs to be 'Right'  The vertical pipe from the bend, and the pipe out the back.

I have a bit of wiggle room because I can move the silencer back and forth and use a longer or shorter bit of tailpipe. I will cut the hole in the bulkhead so as to line up the silencer with where the pipe comes out. Therefore the only place where the pipe length is really critical is the vertical. If my measurements prove inaccurate I will have to just cut a piece of pipe and take it somewhere to be threaded.

 

Welding is not an option for me in this job as a) I don't have a welder b) I don't have 240V on site and c) I don't really have the skills.

[Cheshire cat]

I'm looking forward to seeing the photos on Tuesday!