BMC 1.5 silencer

[Chris Lingwood]

I took my exhaust off to try and get some balast out from behind it. And blow me if it didn't fall apart in my hands. Does anyone have any idea what silencer I might need. The old one has seen better days, and usefully it doesn't have a serial number.

I'll try at the local motor factors but they frown at me when i ask questions like this

[Bones]

I took my exhaust off to try and get some balast out from behind it. And blow me if it didn't fall apart in my hands. Does anyone have any idea what silencer I might need. The old one has seen better days, and usefully it doesn't have a serial number.

I'll try at the local motor factors but they frown at me when i ask questions like this

 

 

Isn't a silencer a silencer? I have two on mine for some reason...........

[David Schweizer]

I took my exhaust off to try and get some balast out from behind it. And blow me if it didn't fall apart in my hands. Does anyone have any idea what silencer I might need. The old one has seen better days, and usefully it doesn't have a serial number.

I'll try at the local motor factors but they frown at me when i ask questions like this

The BMC 1.5 is still one of the commonest engines found on boats, and any decent chandlery should have a selection in stock. Dont throw away the old one, you will need it as a pattern to measure up for the new one as the precise size could depend on the layout of your engine. Alternatively telephone ASAP Supplies (O845 1300870) they stock hundreds of silencers, and offer a swift mail order service.

Edited September 17, 2006 by David Schweizer

[Noah]

Hi Chris

 

When mine fell apart I fitted one of TW Marine's "compact" Hospital Generator silencers. More expensive but I think worth it because it's a lot quieter than the original box. Now I can hear my gearbox rattling and my girlfiend's nagging!

 

http://www.twmarine.co.uk/

 

Noah

[Moley]

Thanks for that link Noah, looks useful.

What sort of numbers are we talking?

 

Our injin'ole fills with exhaust smoke, and I suspect system will fall apart if I get too close and sneeze, so I'll be keeping a close watch on this topic.

 

Can these TW Marine folks supply you with a system if all you can provide are drawings/photos and measurements?

[Chris Lingwood]

Isn't a silencer a silencer? I have two on mine for some reason...........

Not quite. Some engines like to have a specific back presure (how hard it is to force the exhaust gas down the pipe), I'm not sure whether the bmc is or isn't one of these.

 

Dont throw away the old one, you will need it as a pattern to measure up for the new one as the precise size could depend on the layout of your engine.

 

True true. The length of the exhaust is probably just as important. But then again we are asuming that we have the right thing fitted already. Which on this boat is probably giving people a little too much credit. Why are these things never straight forward.

 

Hi Chris

 

When mine fell apart I fitted one of TW Marine's "compact" Hospital Generator silencers. More expensive but I think worth it because it's a lot quieter than the original box. Now I can hear my gearbox rattling and my girlfiend's nagging!

 

http://www.twmarine.co.uk/

 

Noah

 

Interesting. Although I'm not sure it would help that much because for some reason (I expect some one being cheap) I've got solid engine mounts so I get alot of vibration through the hull anyway.

 

 

 

I wonder how upset the motor factors would be if I came in and plonked a rusty old silencer on their nice clean desk and said "one of these please"

[John Orentas]

The last time I bought a silencer, I managed to find a large wholesaler, went in there found one the size I wanted and said I'll have that one.

 

If you want some extra silencing buy the biggest one that will fit into the boat even if you have to re-position the outlet on the hull. Remember that diesel silencers will last many times longer than those fitted to petrol engines, they don't rust from the inside in the same way, simply find one with in/ out diameters about the right size. You will doubtless need a bit of welding done.

Edited September 18, 2006 by John Orentas

[Noah]

Thanks for that link Noah, looks useful.

What sort of numbers are we talking?

 

Our injin'ole fills with exhaust smoke, and I suspect system will fall apart if I get too close and sneeze, so I'll be keeping a close watch on this topic.

 

Can these TW Marine folks supply you with a system if all you can provide are drawings/photos and measurements?

I think I paid about £125 for the silencer but it’s always all the other bits and pieces that bump up the cost (like every job you do on a boat!). TW were very good with advice so I think I got good value overall. John Orentas is moored close by them and I think he’s about to reply to this post with advice!

 

................. John Orentas is moored close by them and I think he’s about to reply to this post with advice!

Yep, beat me to it!

[Canal Shop Man]

 

I wonder how upset the motor factors would be if I came in and plonked a rusty old silencer on their nice clean desk and said "one of these please"

Oh we get that all the time! Diesely bits of pipe, sooted up chimneys, rusty exhausts, it's all part of a days work!

 

We supply 'Hospital' silencers, made to measure in a few days for £145. You should allow for a 30" long by 12" diameter cylinder though to get best results - any smaller will start to limit its effectiveness. They can be delivered if required.

[John Orentas]

Those Hospital silencers that T W Marine (and Canal Shop Man) sell are excellent quality but personally I would be thinking in terms of no more that £40 for a big silencer and there are presumably limitations too with available sizes, my wholesaler chap has hundreds of them in every concievable size and shape.

 

As with most things in life if you can find alternatives to chandlers you will save a lot of money.

Edited September 18, 2006 by John Orentas

[awatsonbcp]

Is a hospital silencer different in construction to an ordinary silencer then ?

[bottle]

Is a hospital silencer different in construction to an ordinary silencer then ?

 

The constrution is the same they are just bigger and more 'efficient' at silencing the noise.

[Yoda]

Not quite. Some engines like to have a specific back presure (how hard it is to force the exhaust gas down the pipe), I'm not sure whether the bmc is or isn't one of these.

True true. The length of the exhaust is probably just as important. But then again we are asuming that we have the right thing fitted already.

 

There are some calculations which I can give you to tune the exhaust system for your engine. There is a distinct relationship between length and diameter. Hey, but get a life!!! As long as the cylinders are fully scavenged then they will be OK. On the other hand if you have a two stroke diesel, the right amout of exhaust back pressure is required to stop the fuel being purged.

[John Orentas]

There are some calculations which I can give you to tune the exhaust system for your engine. There is a distinct relationship between length and diameter. Hey, but get a life!!! As long as the cylinders are fully scavenged then they will be OK. On the other hand if you have a two stroke diesel, the right amout of exhaust back pressure is required to stop the fuel being purged.

 

 

Diesel engines are not critical with regard to exhaust systems, you can assume that as long as the pipe sizes are much the same they will have little effect on engine efficiency. The general rule however is the bigger the silencer the quieter the engine.

 

With a new boat, don't just take the exhaust out of the rear of the stern, why not have the outlet several feet towards the bow, the noise is less intrusive and the fumes disperse before they get to the steerer.

 

With professionally built boats very little thought is ever given to this sort of thing, builders do what is conventional what is simple to engineer .