Author Topic: Muffler for flushing older outboards.  (Read 9789 times)

Offline mckee17

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Muffler for flushing older outboards.
« on: August 11, 2009, 05:02:37 PM »
When flushing my outboard in the driveway I tend to shut it down way to soon so as not to offend the neighbors.  The noise really reverberates throughout the neighborhood.  Came across some old posts on another site where a guy made up his own muffler.  I tried it with some modifications. using common plumbing supplies and some stuff I had lying around the house.  It worked great.  Cut the noise better than half.

First, measure the size of your prop hub.  Then get a flexible rubber coupling.  Mine was 4". Got the parts from Lowes.  Next a 4" PVC clean out fitting with plug.  Also used a 3 1/2" round electrical cover, cut out a gasket from an old rubber backed stair tread.  A 4" galvanized 3/8" bolt, washers, nut and a spring from an old thermostat kit.

Drill 5 - 3/8" holes in the PVC plug and 1-3/8 hole in the center of the elec. cover.  Invert the plug and screw into the clean out fitting. Bolt goes thru center of plug then thru rubber gasket, then elec. cover, then spring, washer and nut.  Spring and gasket are there to relieve excess back pressure in case of a backfire.  (see pics)   This set up also provides needed back pressure for a more thorough flush.
 

« Last Edit: August 11, 2009, 05:12:52 PM by mckee17 »


Offline Still Running

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Re: Muffler for flushing older outboards.
« Reply #1 on: August 11, 2009, 06:04:27 PM »
I am not an outboard guy, but it looks like that may cause too much exhaust back pressure. Witch I think it could cause the cylinders to over heat and damage the engine.
 Just my thought.
I would at least look into that before you run the engine too much.
« Last Edit: August 11, 2009, 06:06:47 PM by Dieselhp »
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Offline mckee17

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Re: Muffler for flushing older outboards.
« Reply #2 on: August 11, 2009, 07:32:07 PM »
Any outboard mechanics out there that would like to chime in on this?  Wouldn't want to damage my engine.  Have used it around 5 times and ran engine for 10 to 15 minutes each time.  No overheating problems so far.

Offline wb

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Re: Muffler for flushing older outboards.
« Reply #3 on: August 12, 2009, 04:11:04 PM »
i only play a mechanic in my mind, but if you got good water flow at the pisser and are running at idle or just above, would be almost impossible to damage the moto unless u got no oil.

jm2c


Offline Maritime Matt

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Re: Muffler for flushing older outboards.
« Reply #4 on: August 12, 2009, 09:37:53 PM »
Not something I would do. Have no idea if it will damage your motor. Flush the motor  til it warms up enough to open the stat and shut er down. Roughly 3-5 minutes. Matt.

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Offline shkbilly

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Re: Muffler for flushing older outboards.
« Reply #5 on: August 22, 2009, 08:31:45 PM »
i only play a mechanic in my mind, but if you got good water flow at the pisser and are running at idle or just above, would be almost impossible to damage the moto unless u got no oil.

jm2c


Not an outboard mechanic, but a mechanic nonetheless.

Too much backpressure would heat the exhaust up and possibly burn a valve. However, I have no way of knowing if the muffler would fall into the category of providing too much backpresure.
Bill
After Ours - 20' Grady Overnighter

 

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