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Thread: Omc 56 tuner questions

  1. #1
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    Default Omc 56 tuner questions

    This might sound a daft question , but what is the hole at the top of the tuner for in the 56 ci OMC 20 inch motors.
    and 3 small holes about 1/th inch in the top of the plate ???
    pic below shows what I mean about large hole.

    I got my spare mid section completely apart yesterday doing some measurements and notices the large hole in the top at the side.
    also took notice of the lots of holes at the top of the can itself.
    Plus something I did not know and never noticed before was the small hole in the water pipe about 8 inches up from the water pump ?

    I noticed that if the tuner was cut about 3 to 3 inches ( from top of adaptor to exhaust outlet end is 11 1/2 inches) it could be made about an inch wider all
    round and STILL fit in the can easy enough , so can be made wider at the bottom.
    (Not sure if I want to cut the one on my engine I use at the moment )

    I also managed to break every single bolt after the very first one came out fine, its like the stainless turns to rubber in aluminium after a while.
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    Default Omc 56 tuner questions

    I think that's an idle exhaust relief? At low speeds of most of the mid section may be submerged, closing off the bottom of the tuner, exhaust is relieved out that upper hole to allow better idle?

    I've heard the OMC 15hp A racers can block that hole for better top end.
    mini tunnel boats for sport, now an experimental Sport C added to the fleet.

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    I was thinking it could be idle relief due to lowest part of exhaust being in water etc, but that seemed to obvious.
    I might be over thinking on this, looking for something that is not there ha ha

    thanks for reply BYOBoat

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    The hole in the water pipe is to allow water to drop over the water pump so that you do not melt the plastic housing. The guys that run the SST 60's usually run the aluminium water pump housing. Sorry to see you broke the bolts, but when a motor is run in saltwater you get a salt build up around the bolts and you should always give plenty of heat around the outside of the bolts and use an impact driver on the bolts. Perseverance is the way rather than brut force.

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    Team Member skeg's Avatar
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    Does the aluminum water pump housing use the same impeller?

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    i did use heat trying to get the bolts undone, its not a case of all being to tight its the bolts are rotten and eaten half way through. i have since got a few out of the threaded with just pliers.
    got 4 to drill out now and use an easy out die to these being a bit tighter. i am gentle when trying to get bolts out of the engine, but when the bolts are such bad quality its a bit hard.
    i know about salt corrosion, its the main problem with most engines over here as we dont find many motors that have never run in it. and so many people dont flus the motors after being
    in the salt.

    Now where the tuner meets the adaptor the square hole for the exhaust in the adaptor has two large what i would call casting flaws, both are identical and opposite each other.
    But i am wondering if these are deliberate to give the exhaust some kind of swirl going out into the tuner, something like this was done back in the 1970's on a Yamaha prototype bike.
    are these normally smoothed out for a better flow or left alone ?
    would it be best to clean out the adaptor of these 2 very large pieces ( i call them flaws) or are they best left in and serve a purpose ?.
    to me it seems a pretty large restriction.

    couple of pics to show what i mean by the " flaws". these could very easily be taken out with a die grinder and the area polished up .
    i am thinking any cleaning up has top help the exhaust exit easier ?

    any thoughts.

    .
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    " Does the aluminum water pump housing use the same impeller? "
    thats a pretty good question, as the two types on the 56 are a 3 blade and a 6 blade... what one for the alloy cover ?

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    Team Member skeg's Avatar
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    Steve, where does one find one of the aluminum water pump housing Was this a factory part?

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