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NewCanalBoy

Finding an exhaust leak ?

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Right, I know I have had a leak in the Flexi part of the exhaust. I have found that the reason the Flexi part broke was that the engine mounts are a bit to flexible - so they are going to be replaced in a couple of weeks. The Flexi exhaust was wrapped up as best I could but not repaired as it could possible break again before the mounts are changed.

 

I believe there might be a small leak still but was wondering how to identify it if it is coming from elsewhere. Obviously there is nothing bellowing out and cannot see anything obvious. But is there any tricks I could use ?

 

Was thinking maybe starting the engine at night and using a torch in the engine bay - would this show up any smoke ?

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Just move your hand over the exhaust (without actually touching it) when the engine is running. You’ll feel any leak puffing out. 

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Normally can see soot from leak another way on cars to locate leak is to get someone to lightly hold a rag over exhaust outlet which increases exhaust pressure for a few seconds at a time  while you look and listen for leak

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10 hours ago, NewCanalBoy said:

Was thinking maybe starting the engine at night and using a torch in the engine bay - would this show up any smoke ?

It might help with nocturnal smoke I guess, but I'd be following the sensible suggestions above. Not the sinking one though, Ok? ;)

 

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3 minutes ago, Sea Dog said:

It might help with nocturnal smoke I guess, but I'd be following the sensible suggestions above. Not the sinking one though, Ok? ;)

 

So @bizzard's idea of using a canary is one of the sensible ones. With a cage made from meccano for it to live in.

Edited by Jen-in-Wellies

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3 minutes ago, Jen-in-Wellies said:

So @bizzard's idea of using a canary is one of the sensible ones. With a cage made from meccano for it to live in.

You're not seriously suggesting that some of @bizzard's well thought out ideas are in some way implausible, are you Jen?

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9 minutes ago, Sea Dog said:

You're not seriously suggesting that some of @bizzard's well thought out ideas are in some way implausible, are you Jen?

Perish the thought. Just confirming that his ideas are firmly on the sensible side.

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2 minutes ago, Jen-in-Wellies said:

Perish the thought. Just confirming that his ideas are firmly on the sensible side.

Yep, sound idea the Canary - Auntie Mary used to have one, apparently. 

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If the leak is on the flexi, simply replace it,it's very cheap.

Had a leak on mine,and found the rough location by giving the engine a good rev and shutting the throttle rapidly.(Might not work if you have a newish engine) but my old BMC 1500 puffed blue smoke from the leak.

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The location of my small  exhaust leak was obvious from the transient puff of smoke on starting the engine from cold.

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Fitting a harder set of engine mounts, I suggest, is not a solution to an exhaust flexing problem.

Whereas it might make the exhaust pipe flex less - it will, almost certainly transmit a lot more noise and vibration to the whole transmission and - more importantly - to the rest of the boat, which will mean discomfort for all.

 

Don't fix one problem only to create another....

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14 minutes ago, OldGoat said:

Fitting a harder set of engine mounts, I suggest, is not a solution to an exhaust flexing problem.

Whereas it might make the exhaust pipe flex less - it will, almost certainly transmit a lot more noise and vibration to the whole transmission and - more importantly - to the rest of the boat, which will mean discomfort for all.

 

Don't fix one problem only to create another....

So shall I leave flexing flexi engine mounts in place that is breaking flexi parts of the exhaust - and just keep repairing flexi parts of the exhaust ?

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Over braided proper flex sections installed with no twist and sufficient length to allow free movement and not bent unduly into an elbow shape will last a long time even with soft mounts. Ensure that the engine does not shunt backwards and forwards unduly under load reversals placing the flex in strain lengthways. Does your prop shaft have a thrust bearing on a cross member behind the gearbox or is all thrust take on the gearbox?

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51 minutes ago, NewCanalBoy said:

So shall I leave flexing flexi engine mounts in place that is breaking flexi parts of the exhaust - and just keep repairing flexi parts of the exhaust ?

If the flexi mounts are rogered, they need changing for some new ones of the right spec. If they're in good shape but the wrong spec, they need changing for the right spec. If they're the right spec and in good shape, leave them alone. Don't mix up the two jobs or compromise on one to mask an issue with the other - get both right. :)

 

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46 minutes ago, Boater Sam said:

Over braided proper flex sections installed with no twist and sufficient length to allow free movement and not bent unduly into an elbow shape will last a long time even with soft mounts. Ensure that the engine does not shunt backwards and forwards unduly under load reversals placing the flex in strain lengthways. Does your prop shaft have a thrust bearing on a cross member behind the gearbox or is all thrust take on the gearbox?

Not sure, I'll take some pictures tomorrow !! I know a have a 'flexi joint' after the gearbox to the prop if that's any good ?!

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To find the leak, take a length of hose pipe, 1-2 metres, hold one end to your ear, the other pass around close to the exhaust whilst the engine is running.

The sound of the leak, will soon be found, even if you cannot see it.

 

Bod

Who has been laughed at before, whilst finding air leaks, with a length of pipe!

  • Greenie 1

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15 hours ago, Boater Sam said:

Does your prop shaft have a thrust bearing on a cross member behind the gearbox or is all thrust take on the gearbox?

I think that's a yes ?

IMG_20190912_113110158__1568284921_94.197.120.105.jpg

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