Replacing my exhaust and how to choose a hospital silencer?

[Boater Sam]

You have no 1 1/2" unions, female to female thread in your list.

You will need at least one possibly two otherwise you will be unable to thread it all together.

This will mess up which male and female threads you need, draw it all out on paper and work  out how you can rotate bits to screw it together, its not  always obvious.

[BWM]

On 15/08/2019 at 13:30, ivan&alice said:

I took the lagging off the silencer now and in my opinion it clearly needs replacing, gunk and tape aren't going to do the trick for long.

Here's some pics to show you guys what I'm talking about.

 

 

There are three big holes and as you can see the whole thing is very rusted and actually spongy around the holes. The lid of the compartment is just a wooden board and is not watertight so rain can get in and drip on the thing. The leak was somewhat contained by the lagging but the worst of it is coming out of the split right at the exhaust end. The compartment actually fills with exhaust fumes and under the piles of rust you can see the compartment is filled with potentially flammable black soot, which is why the BSS examiner was unimpressed.

 

The silencer extends for another 6 inches or so through that bulkhead into the engine bay. Anything larger than it is would involve cutting out a circle, but this shouldn't be too hard to do. If I replace it I may as well upgrade it too.

If i was looking to change that i'd mount the silencer across the boat behind the weed hatch, there are automotive ones available that enter and exit from the same end which might avoid having to move the outlet. I wouldn't worry too much about bends on a system that short, there are plenty of rear engined high performance cars with pipes resembling a box of snakes. I would imagine that the exhaust as it is would be transmitting vibration into the hull, so rerouting it will drop noise levels on its own. 

[Tony Brooks]

10 minutes ago, BWM said:

If i was looking to change that i'd mount the silencer across the boat behind the weed hatch, there are automotive ones available that enter and exit from the same end which might avoid having to move the outlet. I wouldn't worry too much about bends on a system that short, there are plenty of rear engined high performance cars with pipes resembling a box of snakes. I would imagine that the exhaust as it is would be transmitting vibration into the hull, so rerouting it will drop noise levels on its own. 

I think that you will find those boxes of snakes are  tuned exhausts where at certain speeds the pulse of exhaust gasses from a previous exhaust stroke is used to help draw the gasses out of the cylinder on the next power stroke.  Whilst for inland marine use elbows might be OK it is still poor practice to use them on exhaust systems, use bends instead.

[BWM]

9 hours ago, Tony Brooks said:

I think that you will find those boxes of snakes are  tuned exhausts where at certain speeds the pulse of exhaust gasses from a previous exhaust stroke is used to help draw the gasses out of the cylinder on the next power stroke.  Whilst for inland marine use elbows might be OK it is still poor practice to use them on exhaust systems, use bends instead.

I can't disagree with that, just pointing out that there is often more available from sources other than chandlery when problem solving. An independent exhaust supplier would normally be able to supply the necessary if given the plan and dimensions, both cheaper and proper components. 

[jetzi]

10 hours ago, Boater Sam said:

You have no 1 1/2" unions, female to female thread in your list.

You will need at least one possibly two otherwise you will be unable to thread it all together.

This will mess up which male and female threads you need, draw it all out on paper and work  out how you can rotate bits to screw it together, its not  always obvious.

Hmm, I have one female to female "socket": (Malleable Iron Socket 1.5" BSP (female to female))

I thought this was the union I needed - although I see there is this union too: https://www.midlandchandlers.co.uk/products/mall-iron-pipe-union-1-1-2-bsp-ea-065

 

Is a socket different to a union? The union is considerably more expensive.

 

The only place I need a union is to connect the tailpipe to the silencer outlet. The rest of the components are all male-to-female. I didn't draw it out but that list is all the components in order and I made sure that females followed males and vice versa.

 

10 hours ago, BWM said:

If i was looking to change that i'd mount the silencer across the boat behind the weed hatch, there are automotive ones available that enter and exit from the same end which might avoid having to move the outlet. I wouldn't worry too much about bends on a system that short, there are plenty of rear engined high performance cars with pipes resembling a box of snakes. I would imagine that the exhaust as it is would be transmitting vibration into the hull, so rerouting it will drop noise levels on its own. 

Do you mean mount the silencer externally outside the hull across and behind the boat?? Apart from looking horrible it would leave it incredibly exposed to the elements, bumps and bruises and seems likely to elevate noise levels than an internally mounted one. As for vibration into the hull, I am hoping that the flexible exhaust pipe ( 24" Flexible Exhaust Pipe ) will absorb some of it. I currently have two sections of this pipe in my exhaust system.

 

Speaking of vibrations, one thing I'm not too sure about is how I'm going to mount the silencer. It is going to be fairly close to the deck and there is a vertical support that I would be able to drill holes through. I imagine that the silencer will be reasonably heavy and need support beyond just where it rests on the bulkhead. What would be the preferred way to mount this? 40 odd inch long steel cable ties? Some kind of rubber damper?

 

10 hours ago, Tony Brooks said:

Whilst for inland marine use elbows might be OK it is still poor practice to use them on exhaust systems, use bends instead.

I may as well use a bend as I have the space. And I will only need the one bend if I buy a side entry silencer.

 

1 hour ago, BWM said:

I can't disagree with that, just pointing out that there is often more available from sources other than chandlery when problem solving. An independent exhaust supplier would normally be able to supply the necessary if given the plan and dimensions, both cheaper and proper components. 

I like the idea of saving money because over 400 GBP for a new exhaust system hurts a lot. But I have never heard a diesel car as quiet as a hospital-silencer-equipped narrowboat. Also I did take a look at automotive exhaust pieces, they all seem to require welding rather than simply screwing together. Welding is going to be a difficult thing to do on the towpath, given that I have no 240V, no welding equipment, and only around 2 hours of experience in welding. If someone could suggest an automotive exhaust system that would be comparable, I'm all ears!

[BWM]

2 hours ago, ivan&alice said:

Hmm, I have one female to female "socket": (Malleable Iron Socket 1.5" BSP (female to female))

I thought this was the union I needed - although I see there is this union too: https://www.midlandchandlers.co.uk/products/mall-iron-pipe-union-1-1-2-bsp-ea-065

 

Is a socket different to a union? The union is considerably more expensive.

 

The only place I need a union is to connect the tailpipe to the silencer outlet. The rest of the components are all male-to-female. I didn't draw it out but that list is all the components in order and I made sure that females followed males and vice versa.

 

Do you mean mount the silencer externally outside the hull across and behind the boat?? Apart from looking horrible it would leave it incredibly exposed to the elements, bumps and bruises and seems likely to elevate noise levels than an internally mounted one. As for vibration into the hull, I am hoping that the flexible exhaust pipe ( 24" Flexible Exhaust Pipe ) will absorb some of it. I currently have two sections of this pipe in my exhaust system.

 

Speaking of vibrations, one thing I'm not too sure about is how I'm going to mount the silencer. It is going to be fairly close to the deck and there is a vertical support that I would be able to drill holes through. I imagine that the silencer will be reasonably heavy and need support beyond just where it rests on the bulkhead. What would be the preferred way to mount this? 40 odd inch long steel cable ties? Some kind of rubber damper?

 

I may as well use a bend as I have the space. And I will only need the one bend if I buy a side entry silencer.

 

I like the idea of saving money because over 400 GBP for a new exhaust system hurts a lot. But I have never heard a diesel car as quiet as a hospital-silencer-equipped narrowboat. Also I did take a look at automotive exhaust pieces, they all seem to require welding rather than simply screwing together. Welding is going to be a difficult thing to do on the towpath, given that I have no 240V, no welding equipment, and only around 2 hours of experience in welding. If someone could suggest an automotive exhaust system that would be comparable, I'm all ears!

It would need to be mounted inside, outside would be quite absurd in both looks and performance, and there appears to be space. It could be mounted on welded upstands with some form of rubber involved. 

 You would be best finding an independent exhaust to discuss what is suitable and available. There are plenty of pushfit/clamped components about, most automotive systems are such.

[jetzi]

4 minutes ago, BWM said:

It would need to be mounted inside, outside would be quite absurd in both looks and performance, and there appears to be space. It could be mounted on welded upstands with some form of rubber involved. 

 You would be best finding an independent exhaust to discuss what is suitable and available. There are plenty of pushfit/clamped components about, most automotive systems are such.

There is not space, as under the deck at the back is the rudder tube. Mounting the silencer beam-wise on the inside would render the weed hatch inaccessible.

 

Are you suggesting I go to an auto exhaust centre and discuss with them? I guess I can try that...

[Tony Brooks]

Probably best to go to an exhaust specialist and not the likes of Quickfit.

[nb Innisfree]

I looked at ready made silencers for Innisfree but none were the size I wanted so I went straight to the manufacturers (Servais) who made one to my dimensions (as big as poss) They made a lovely solid job of it and it was much cheaper. 

[BWM]

1 hour ago, ivan&alice said:

There is not space, as under the deck at the back is the rudder tube. Mounting the silencer beam-wise on the inside would render the weed hatch inaccessible.

 

Are you suggesting I go to an auto exhaust centre and discuss with them? I guess I can try that...

It's hard to ascertain what spac9e you have available from the picture, but there are various shapes available such as flattened oval, etc. Yes, i'd speak to the experts. To give an example, a custom system for my vehicle in stainless would work out at about £450, at approximately 12' in length with two silencers and an expansion box. Perhaps look at mounting in the engine bay as you mentioned earlier if space is an issue out back. 

Edited August 19, 2019 by BWM

[David Mack]

5 hours ago, ivan&alice said:

 

5 hours ago, ivan&alice said:

 

Is a socket different to a union? The union is considerably more expensive.

 

The only place I need a union is to connect the tailpipe to the silencer outlet. The rest of the components are all male-to-female. I didn't draw it out but that list is all the components in order and I made sure that females followed males and vice versa.

 

A socket us just a short length of pioe internally threaded at both ends.  A union comprises three pieces - a piece at each end which is internally threaded to attach to lengths of pipe (or male threaded fittings) together with a nut to hold the two pieces together. If you can rotate the pipework to one side of the joint a socket will be fine.  If you can't then you need to use a union.

You need to work out the order in which you are going to assemble it all in order to work out which fittings you need.  You may well be able to screw pipes/fittings working away from the silencer in both directions, with the last action being to bolt the engine flange back onto the manifold.

You don't need to worry about which direction the make and female threads run. If the joint us tight it won't lesk anyway. If it is loose it may leak whichever way the threads are pointing.

I suspect Midland Chandlers is not the cheapest place to buy pipe fittings. Try your local plumbers merchant (trade place, not DIY shed) or eBay, or google "iron pipe fittings" for other online suppliers.

Edited August 19, 2019 by David Mack

[Boater Sam]

5 hours ago, ivan&alice said:

Hmm, I have one female to female "socket": (Malleable Iron Socket 1.5" BSP (female to female))

I thought this was the union I needed - although I see there is this union too: https://www.midlandchandlers.co.uk/products/mall-iron-pipe-union-1-1-2-bsp-ea-065

 

Is a socket different to a union? The union is considerably more expensive.

 

The only place I need a union is to connect the tailpipe to the silencer outlet. The rest of the components are all male-to-female. I didn't draw it out but that list is all the components in order and I made sure that females followed males and vice versa.

 

 

Consider how you will be able to remove the engine when you need to without unscrewing all the exhaust from the rear end because after a month you will not be able to undo any of the threaded joints.

[ditchcrawler]

7 hours ago, BWM said:

I can't disagree with that, just pointing out that there is often more available from sources other than chandlery when problem solving. An independent exhaust supplier would normally be able to supply the necessary if given the plan and dimensions, both cheaper and proper components. 

I have never seen a car exhaust terminat in 1 1/2" bsp I also wouldn't be happy with the flexible sections they use. car exhausts are normally on very flexible mounts like large elastic bands

 

Edited August 19, 2019 by ditchcrawler

[BWM]

Just now, ditchcrawler said:

I have never seen a car exhaust terminat in 1 1/2" bsp

I assume you mean the engine end? A simple adapter can be welded up by a competent exhaust outfit using the original flange or similar.

 I often find that trade engineers have a broader mind when problem solving than someone used to using chandlery supplies alone, as you can see from the many fudges and compromises found on many canal boats. 

[jetzi]

I've been a right horse chestnut. I just re-measured everything (measure twice, cut once an all) and turns out that my current fittings are all 2", not 1.5"! I blame trying to measure cylinders without owning calipers.

 

Back to the drawing board.. and back to TW marine with my hat in my hands...

Anyone know the dimensions of a 2" 90 degree bend? i.e., if you were to fit it into a rectangular box, how big would the box be? I want to know how much I should take off the length of the silencer. From the picture I estimate it's three times as long as the diameter, so 6 inches?

2 hours ago, Boater Sam said:

Consider how you will be able to remove the engine when you need to without unscrewing all the exhaust from the rear end because after a month you will not be able to undo any of the threaded joints.

Even with Copaslip?

 

2 hours ago, ditchcrawler said:

I have never seen a car exhaust terminat in 1 1/2" bsp I also wouldn't be happy with the flexible sections they use. car exhausts are normally on very flexible mounts like large elastic bands

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

 

 

[David Mack]

Some fitting dimensions given at https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.cranefs.com/m/5bcdc3dd43687/file/CraneFS_Pipe_Fittings_Brochure_0416.pdf&ved=2ahUKEwjD5KTSqo_kAhVkt3EKHZ0nCBgQFjAAegQIAhAB&usg=AOvVaw3IkLsl66EFNR2cx2p3yqa1

[hawkesmith]

"I think that you will find those boxes of snakes are  tuned exhausts where at certain speeds the pulse of exhaust gasses from a previous exhaust stroke is used to help draw the gasses out of the cylinder on the next power stroke.  Whilst for inland marine use elbows might be OK it is still poor practice to use them on exhaust systems, use bends instead".

 

Just to be a bit more accurate... the back pressure is designed to keep the fresh charge of fuel in,  then purge itself. If an exhaust breaths too easily it will purge the cylinder of fresh charge before the valve closes and so detune the engine. The next time you hear a car or a bike with those 'orrible noisy exhausts you can be smug in the knowledge that they are probably going slower than the standard set up.

 

I know Aprilias; if you listen to the official Akropovic race pipe it is substantially quieter than the Austin racing end can. The Austin system wrecks the bikes performance.

[ditchcrawler]

55 minutes ago, ivan&alice said:

I've been a right horse chestnut. I just re-measured everything (measure twice, cut once an all) and turns out that my current fittings are all 2", not 1.5"! I blame trying to measure cylinders without owning calipers.

 

Back to the drawing board.. and back to TW marine with my hat in my hands...

Anyone know the dimensions of a 2" 90 degree bend? i.e., if you were to fit it into a rectangular box, how big would the box be? I want to know how much I should take off the length of the silencer. From the picture I estimate it's three times as long as the diameter, so 6 inches?

Even with Copaslip?

 

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

 

 

Try this for dimensions, not read it all https://www.cranefs.com/page/downloads/company-brochures/pipe-fittings

 

Even with Coperslip after a couple of years you will struggle.

 

On my boat one end is rigidly mounted to a shaky old diesel engine and the other to a flange in the roof.

Edited August 19, 2019 by ditchcrawler

[Boater Sam]

You seem to be confused about pipe sizes.

Practically every modern engined boat I have ever seen uses 1 1/2" BSP pipe and fittings, that's 1 1/2" internal bore with standard steel tube, the outside is around 2"

You buy on the BSP size not the OD. The fittings do have the size cast in if you can read them through the rust. High pressure steam pipe is thicker wall but uses the same size fittings.

2" BSP is huge compared.

[jetzi]

7 minutes ago, Boater Sam said:

You seem to be confused about pipe sizes.

Practically every modern engined boat I have ever seen uses 1 1/2" BSP pipe and fittings, that's 1 1/2" internal bore with standard steel tube, the outside is around 2"

You buy on the BSP size not the OD. The fittings do have the size cast in if you can read them through the rust. High pressure steam pipe is thicker wall but uses the same size fittings.

2" BSP is huge compared.

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?

[jetzi]

 

If I did go ahead with 2" fittings, assuming I could get an exhaust flange to fit or fit a reducer, could this not improve engine performance through reduced back pressure?

[Bod]

Rusted threads.

Liberal soaking in "Plus Gas" possibly 3-4 times daily, to allow soaking in.

For rusted nuts, a "Nut Splitter" is the final resort.

Plus gas is a well known, old fashioned product, that is still available under that name.  There are other penetrating fluids, all work much the same, by allowing a thin lubricating fluid to creep along the threads, hence the need on longer threads, for repeated applications.

Nut splitters, act by, destroying the nut by splitting the nut with a wedge.  Works better than hammer and chisel, or hacksaw. 

Pipe threads, have 2 Stillson pipe wrenches, one to turn the pipe, the other to support the stationary part.  Ensure the teeth are clean and reasonable sharp, less likely to slip, but will mark the pipe.

 

Bod 

[ditchcrawler]

51 minutes ago, Bod said:

Rusted threads.

Liberal soaking in "Plus Gas" possibly 3-4 times daily, to allow soaking in.

 

Not to be confused with WD40 which wont do the job

[Cheshire cat]

Actually WD40 is just a brand now. One of the lines is penetrating fluid. It's available from Wickes.

[jetzi]

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).