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Mike the Boilerman

Quietening a semi-diesel exhaust

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Well those of you who attended Braunston will appreciate just how loud the exhaust is on the Skandia now installed in the REGINALD. (And it turns out the LING has a similar problem with the Bolinder recently fitted too.) The exhaust is just far too loud to tolerate really, so I need to quieten it substantially.

 

REGINALD's exhaust comprises three feet of 115mm diameter vertical steel tube from the expansion box outlet flange to the roof flange. The roof flange reduces the diameter to about 80mm briefly, then there is a 600mm tall pipe 100mm in diameter on the outside.

 

Simon is of the opinion that the roof flange needs changing as that reduction in diameter is half the trouble. I'm inclined to agree as when the engine was running in Mikes garden before I bought it, neither of us noticed the exhaust being especially loud, and this was with just a two foot length of bendy air conditioning flexi tube stuck on the outlet of the expansion box. I still had that bit of flexi tube until Sunday, when I put it onto the roof flange and ran the engine. It softened the bark a little, but not that much. Then I opened the throttle and it was thrown 40 ft into the air, landed in the middle of the cut and sank immediately so that little experiment ended prematurely :-/

 

I had a chat with Nick Alsop at TW Marine (who seems to know everything about exhausts) and his view was that I needed to put a feckin' great silencer on the engine outlet. But perhaps he would say this, as he sells silencers!

 

So, I'm wondering if anyone here has any comment to make or advice to give. And I wonder why hit-and-miss Bolinder exhausts seem to make so much less noise - is it just because they are smaller capacity engines? perhaps?

 

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Well I think to some extent the capacity will make a little difference, but then have you heard the noise a 50cc race bike makes?

 

The pinch will make a difference, it will cause the pressure waves to bounce back and reverberate inside the egg-sauce. As to your best bet I'm really not sure, it could be that removing the pinch really makes it quiet, but then each system has its own foibles and no two engines will ever sound alike. Toughie.

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Don't you, Mr Motor Torpedo Boat dare to come popping and clattering up the Stort with that thing and disturbing the tranquility like Mark99 has threatened to do unless yew bung the biggest Hospital silencer possible on it. smile.png

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Mike, your mate is right, a feckin great great 12 inch Kenworth vertical stack. If your the type make it polished stainless steel for bling. The 28swg version. Would be best. You can get them in 14inch diameter.

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Hi Mike

 

I would suggest that it is indeed the reduction from 115mm to 80 speeding up the exhaust gas causing the extra noise, just like a stinger pipe does on a racing two-stroke.

 

Maybe another expansion box ( like the one you have on Aldebaran ) would slow the gas before it goes through the roof flange?

 

Alternatively,

If I had to buy a silencer I would go to a tractor dealership and have a look at what they have.

I have run a box from a Ford 4600 on my Landrover Series 2A for years. Hefty kit. New Holland supply old Ford parts.

 

I plan to fit the same to the BD3 when it needs a new one.

Sensible sound but not restrictive.

 

Cheers Bill

Edited by BD3Bill

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Hi Mike

 

I would suggest that it is indeed the reduction from 115mm to 80 speeding up the exhaust gas causing the extra noise, just like a stinger pipe does on a racing two-stroke.

 

Maybe another expansion box ( like the one you have on Aldebaran ) would slow the gas before it goes through the roof flange?

 

Alternatively,

If I had to buy a silencer I would go to a tractor dealership and have a look at what they have.

I have run a box from a Ford 4600 on my Landrover Series 2A for years. Hefty kit. New Holland supply old Ford parts.

 

I plan to fit the same to the BD3 when it needs a new one.

Sensible sound but not restrictive.

 

Cheers Bill

 

Jon Deere for the BD3

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I have a spare silencer 570mm long 2" BSP inlet and offset 2" BSP outlet complete with blingy perforated brass shroud.......... :)

 

Seriously you are welcome to use my silencer for a trial. Tis in the boot of car. Together with a bendy air conditioner tube 4" dia spare that's gonna be chucked (only £7 in B+Q).

 

20150422_190057_resized_1_zpsve2lpcua.jp

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The Bolinder in Ling is a noisy beast and blew a hole in my workshop roof when I owned it. The mrs loathed it with a passion! Skandias have a hell of a bark too.

 

It is easy enough to get a bespoke silencer made and it is cheaper than you may think. We use MIJ exhausts to make up silencers for us and they work very well.

 

Worth a try I would have thought

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The Bolinder in Ling is a noisy beast and blew a hole in my workshop roof when I owned it. The mrs loathed it with a passion! Skandias have a hell of a bark too.

 

It is easy enough to get a bespoke silencer made and it is cheaper than you may think. We use MIJ exhausts to make up silencers for us and they work very well.

 

Worth a try I would have thought

 

 

Thanks! Just had a look at MIJ's ebay shop and they have what looks like just the job.

 

http://www.ebay.co.uk/itm/8-Silencer-Box-3-3-5-4-4-5-Inch-Inlet-Lorry-Van-Truck-Tractor-Scania-Iveco-/221150403144?pt=LH_DefaultDomain_3&var=&hash=item7919ab9b5b

 

Except that at 46" long it aint gonna fit... Time to seef they'll make a short one. Or get TW Marine to do it!

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I would be inclined to see what an unrestricted exhaust does. But before you cut a larger hole in the cabin roof try a length of that flexi pipe straight on the expansion box, and curving gently to pass through the side door (or pigeon box hole in the roof if you have one). You could experiment with different lengths to see what the overall effect is.

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I have a spare silencer 570mm long 2" BSP inlet and offset 2" BSP outlet complete with blingy perforated brass shroud.......... smile.png

 

Seriously you are welcome to use my silencer for a trial. Tis in the boot of car. Together with a bendy air conditioner tube 4" dia spare that's gonna be chucked (only £7 in B+Q).

 

Thanks Mark. Would be interesting to try sticking it on the outlet to see, even though it's far smaller in diameter. Were are you/where is it?

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When I had the Seffle it had a straight through exhaust - probably about 4", I can't remember. It made, IMO, a satisfying deep pop-pop-pop sound. The only time I found it a bit much was when I was belting through tunnels. I then wore ear defenders!

 

I hope a lorry exhaust won't interfere with the production of impressive smoke rings.

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Thanks Mark. Would be interesting to try sticking it on the outlet to see, even though it's far smaller in diameter. Were are you/where is it?

 

 

Carshalton Beeches near Sutton which is a bit out your way I guess. If you are ever over this way it's available.

 

The 4" flexi is in large B+Q's at about 1 m lengths.

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If you really want a deafening blaring exhaust bark use big bore copper tube. I once brazed one up a system for a bloke who owned a 1924 Bentley 3litre red label speed model, it sounded awful, the bloke was bonkers.

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Bolinders have a bark which is sharper when everything is CLEAN - after a while a layer of carbon

builds up on the inside of the expansion box and exhaust pipe which softens the bark, until it reaches

the point where it all needs a good clean - don't know if the same is true of your skandia but if you can

put up with it for a while it may get better, it does however increase the quantity of black smuts when

running hard (in your tea, on your face, on the cabin top etc.)

 

I suspect that any baffling will affect the production of smoke rings.

 

springy

 

ETA does the tallpipe take it over head height ?

Edited by springy

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Bolinders have a bark which is sharper when everything is CLEAN - after a while a layer of carbon

builds up on the inside of the expansion box and exhaust pipe which softens the bark, until it reaches

the point where it all needs a good clean - don't know if the same is true of your skandia but if you can

put up with it for a while it may get better, it does however increase the quantity of black smuts when

running hard (in your tea, on your face, on the cabin top etc.)

 

I suspect that any baffling will affect the production of smoke rings.

 

springy

 

ETA does the tallpipe take it over head height ?

 

 

I'd say yes, just a little above head height.

 

An interesting thing is putting a length of 4" plastic drain pipe on instead of the metal tall pipe softens the noise. Not a lot, but noticably. I'm inclined to think an absorbtion type silencer will have the same effect but more so. Will see if I can find a lorry one and plug it onto the roof collar. If it works, then get it installed properly inside the engine room.

 

Shouldn't affect the smoke rings either, as they are 'straight through'.

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Bolinders have a bark which is sharper when everything is CLEAN - after a while a layer of carbon

builds up on the inside of the expansion box and exhaust pipe which softens the bark, until it reaches

the point where it all needs a good clean - don't know if the same is true of your skandia but if you can

put up with it for a while it may get better, it does however increase the quantity of black smuts when

running hard (in your tea, on your face, on the cabin top etc.)

 

I suspect that any baffling will affect the production of smoke rings.

 

springy

 

ETA does the tallpipe take it over head height ?

A rifled bore exhaust pipe should make the rings spin too.

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Is the answer not more expansion volume? Or to plagiarise another post:ninja.gif -

 

 

Posted 31 July 2015 - 11:48 AM

Hmmm, I think an expansion box would need to be 6" to 8" in diameter to have a noticeable effect on the sound...

  • rep_up.png
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A wise man knows his ignorance; a fool thinks he knows everything.

"Unknown"
Edited by jonesthenuke

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Won't the exhaust scavenging (important on a two stroke) be affected by any reduction in diameter from factory standar? That's also why they have those great big exhaust expansion box's.

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Won't the exhaust scavenging (important on a two stroke) be affected by any reduction in diameter from factory standar? That's also why they have those great big exhaust expansion box's.

 

 

This is my concern too, and why I wasn't planning to take the advice I dished out and was quoted earlier for adjusting the exhaust note on a four stroke Gardner.

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Mike, your mate is right, a feckin great great 12 inch Kenworth vertical stack. If your the type make it polished stainless steel for bling. The 28swg version. Would be best. You can get them in 14inch diameter.

 

There's a narrowboat around here with a big Eminox stack up the back, sounds lovely.

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Kevin Whittles book page 123 gives some good info re exhausts. Semi diesels need to push out gas with little effort (big exhaust dia) and he makes the point that the big expansion box reduces gas velocity (and harshness of ex. noise) and one should consider entering expansion box (note no silencer) in one dia and exiting in a bigger diameter.

Edited by mark99

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