Air cooled yamaha 2 stroke outboard 5hp

Discussion in 'Outboards' started by valvebounce, Feb 13, 2015.

  1. valvebounce
    Joined: Dec 2010
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    valvebounce Senior Member

    I bought a boat with a 5hp yamaha 2 stroke engine on it.
    I do believe it is air cooled.
    Is it possible to run the engine out of the water?
    Could be handy for doing repairs etc.
     
  2. gonzo
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    gonzo Senior Member

    Is the exhaust dry or water cooled?
     
  3. valvebounce
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    valvebounce Senior Member

    Hi Gonzo,I am not sure.
    There is a 1/4"hole at the cavity plate level at the front of the casing,and a square 1" exit for the exhaust just above and slightly beyond the prop.
    I can't see any other inlet for the water.
     
  4. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    Perhaps attached manual may be helpful. You can always visit the Yamaha website. I have not seen there outboard engines air cooled.
    These engines, I do not know if other types should, can´t work if water does not enters through the water inlet hole. You can make it work within a container of water (remove the propeller first).
     

    Attached Files:

  5. valvebounce
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    valvebounce Senior Member

    Very much obliged for the information TANSL.
    Valvebounce
     
  6. SukiSolo
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    SukiSolo Senior Member

    If you don't have a service record for the engine, or know the previous owner did the service correctly, I think a full service would be in order. One of the main things with these (pretty much all small outboards) is ensuring the impellor is changed annually. Most small engines are water cooled bar the small Hondas' AFAIK.

    I've done a few small Yams' and they are straight forward, but you will need a high quality socket set to get to the impellor housing without stripping the nut heads. These water cooled units require lubrication ie water in the housing to allow the impellor to rotate without tearing themselves to bits. If you want to test, put it on a stand and wheel it into a lake, or put in a bin part full of water then start it. Do not be tempted to run it dry as that will almost certainly wreck the impellor. The engine itself can run without water for several minutes with no harm - it is the impellor that gets damaged.

    If the impellor has not been changed for some time, it could disintegrate on removal. One tip is to ensure you do not lose the keyway for the impellor. In practice disassemble on hard ground ie concrete or wood floor with no gaps. You should also be able to find quite a few guides to things such as draining/refilling the gearbox oil to correct level etc. Generally if the motor has done a while without the gear oil change, what comes out will be clean but a bit milky/cloudy because of very slight water contamination.

    I note that the Manual does not in fact cover the impellor, but it is in the housing of the lower plate which is dropped down once you have the prop off and with gearbox drained. If it is like the smaller 2-3Hp units one of the plate holding bolts attaches the anode too. Yamaha sell the full service kit with impellor and it is not expensive. I have found them a bit easier to work on than the Mariner equivalents, even though they are often licensed copy type engines. A little more finger access, better impellor keyway etc.
     
  7. valvebounce
    Joined: Dec 2010
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    valvebounce Senior Member

    Thanks for your reply SS.
    this engine came on a Skipper dinghy that I purchased,it starts well,and goes in and out of gear easily.I have run it in a tub.
    It is a single cylinder,and the engine is encased with an ally cover,under the main cover.
    I have a 6hp Evinrude,plus a 3.3hp evinrude,they both have impellars.
    From what I can gather,these yamaha engines are pretty noisy because they are aircooled.I think they need to be in water because of exhaust cooling,or the heat blisters the paint.
    I have a decent set of tools,so I will drop the bottom section and have a look.
    The Dinghy only weighs 168lbs unladen,so I am hoping it will get on the plane with the 5hp and 6hp engines.
    Thanks again for your reply.
     
  8. SukiSolo
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    SukiSolo Senior Member

    Well the little 2Hp Yam is water cooled... at least it has an impellor, as I have changed a couple of these. I'd be very surprised if the 5Hp is air cooled - look for significant finning of the engine block, with the cover off. Think lawn mower engine type finning or static generator.

    The manual (as linked by Tansl) shows a similar arrangement to the 2 and 3.5? models of old. All the current portable models are water cooled at this small end of the range. Current ones have a thermostatic valve, which will open when required. This arrangement lets the engine get to optimum operating temp and then stay in that window.
     
  9. valvebounce
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    valvebounce Senior Member

    I must admit I was surprised at it being aircooled,I didn't realise that when I bought it.I saw one on ebay the other day,which made me curious to find out about it.I looked on Utube,and there was a couple of vids with them being used.
    I looked for the finning,it can be seen on the underside of the engine,the rest is encased in an aluminium cover,which I think probably directs the airflow around the engine.
    I have changed the impellor on my 3.3hp-6hp and 18hp Evinrudes.
    I have 2 British Seagulls,a 40+ and a 40-.They have the same sized engine but a different gearbox and prop size,unfortunately they have no neutral,so they are a bit of a pain,I have them running sweet as a nut.
    The Seagulls are ok on my 10ft fibreglass rowing boat,but I prefer the more modern engines.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    I know nuffink about the peculiarities of this particular motor, which was also a Mariner (?) or one or two other brands, possibly, but you could notice they were loud. As always, it is far better to have the manual for the engine at hand, before doing anything with it.
     
  11. SukiSolo
    Joined: Dec 2012
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    SukiSolo Senior Member

    I did a bit more digging. The 5Hp Yam and Mariner 2 strokes were air cooled in the early 70s'! so pretty old models. There may still be an issue with the exhaust having an impellor to cool or quieten it down. I've only worked on stuff from the late 80s' on regarding outboards and your motor is pretty ancient. Still if it's in good nick it should be OK though it will be LOUD by modern standards. Possibly the unit is the same age as the Skipper which would be early 70s' at a guess.

    Still worth dropping the prop and shaft and replacing the gear oil etc. This will also reveal if it does have an impellor for the exhaust and allow you to clean out any insects etc that may have made the passageways home....;)
    A piece of strimmer line can help unblock any air/water ways with minimal damage, along with a little compressed air.
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    Those air-cooled 5hp motors, under various brand names, were still being marketed much more recently than the 1970's. I can still hear the noise !
     
  13. valvebounce
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    valvebounce Senior Member

    Hi Mr E,
    I'll be going over it before I use it,I can probably get the info on google.
    There's a couple of nice calm rivers to try it on before I use it in the sea.
    No Bull sharks and salt water crocs.:D
     

  14. valvebounce
    Joined: Dec 2010
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    valvebounce Senior Member

    Thanks for doing the digging SS,
    I always get motors running sweet and reliable,it's a hobby.
    Woke up to a beautiful day up here,so I will be out there fiddlin' shortly.
    Got a couple of boat trailers that need a bit of looking at,I have converted one from classic mini wheels to 13" micra wheels.It puts the trailer slightly higher,but with less revolutions and wider tyres it rides much better.
    W
     
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