Need help on old Yamaha 5b (2stroke 5hp)

Discussion in 'Outboards' started by Herr Bolus, Aug 9, 2008.

  1. Herr Bolus
    Joined: Aug 2008
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    Location: holland

    Herr Bolus New Member

    Hi,

    I've resently obtained an old but in good shape yamaha 5b (don't know the year think somewhere 80's)
    The only problem is that the water-cooling doesn't work.

    I've looked everywhere on the internet but just can't find a manual wich i can download to look up how to fix the problem.

    Also tryed looking everywhere to find the impeller in the motor it's not in the lower unit and looked everywhere on the motor itself at least the parts i could get off, there's one thing (don't know the english name), with wich you generate power for the sparkplug, i just couldn't get it off so i'm not able to check if the impeller is underneath it?

    Now can it be that the impeller is exactly where i can't get to or there is no impeller?
    It's aircooled but i;m sure it's also watercooled because it has a water intake behind the propeller and pee-holes in the mid section...

    So my question is if anybody knows how to fix this problem (or how the cooling/pumping works where i can find the damn impeller?) or were i can find a good site to look up a manual of this type.

    Thank you very much for your help and time.
     
  2. Herr Bolus
    Joined: Aug 2008
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    Herr Bolus New Member

    Ok i've had a better look
    now i've got the thing off i was talking about
    but don't think the impeller is there because then it should be in the "carter".

    So i'm starting to think there is no impeller,
    can it be that the propellor pushes the water thru the system?

    I also put a hose on the water intake to check if its blokked or anything but it all looks fine except for that the water is not exiting the pee-holes.

    Thank you.
     
  3. Knut Sand
    Joined: Apr 2003
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    Knut Sand Senior Member

    Very old Tohatsu were at least air-cooled.... Had one 5 hp of those....
    Don't know about this one though, easy to see on the sylinder....;)

    But I have also seen engines with cooling intake on top (ehh bottom of, of course) of the cavitation plate, behind the propeller, the wash from the propeller doing the job for the impeller, don't recall the make though....

    Edit; have you tried with a thin steel thread to poke up the holes?
     
  4. Herr Bolus
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    Herr Bolus New Member

    Yeah the cilinder has indeed water pipes going thru.
    And when i run the engine there is exhaust air coming not only from the tail right above the propeller but also from the pee-holes.
    So i'm not exactly sure how things should look from the inside of the mid-section (where the pee-holes are) but maybe these holes are not connected properly to the cooling-water?

    what do you think/know?

    and yeah also poked up the holes already.
     
  5. kenJ
    Joined: Jul 2005
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    Location: Williamsburg, VA

    kenJ Senior Member

    on most small outboard the impeller is part of the lower unit. It is powered by the drive shaft. Figure out how to disconnect the shift linkage. Either at the top by the shift lever or on the side of the shaft behind at rubber plug. Remove the lower unit by removing the 2 or 3 bolts that hold it in place. The impeller housing should now be visible. replace impeller, there is usually a small roller pin that slides into a slot to act as a key. When you reinstall the lower unit ensure the water delivery tube goes into the impeller outlet port.
     
  6. Herr Bolus
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    Herr Bolus New Member

    Yes i already figured that out for myself and i had the whole lower unit removed.
    But there was no impeller nor housing and the copper tube wich hangs behind the propellor went all the way up straight to the engine thru the cillinder and back to the tail.

    Now this means that or the impeller (or what other kind of pump) is in the "Carter", but don't think so because this would mean to replace the impeller, what everybody should be abel to do very easily, you have to take half the engine a part.

    Or it's like this that there is no impeller and that the propellor should pomp/push the water tru the pipes. (don't know but maybe they did this with older type's???)
    But then again when i run the engine there is no water coming from the pee-holes except exhaust air (maybe not connected properly?)
    And also checked all the water pipes for blockage, there are none except for again no water exiting from pee-holes.

    I carefully let the engine run for a short while, whilst checking the temperature constantly.
    But i think it's still getting pretty hot, if i touch it much longer than 1 sec i would probably get a small burn...

    thank you for the reply
     
  7. kenJ
    Joined: Jul 2005
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    kenJ Senior Member

  8. Knut Sand
    Joined: Apr 2003
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    Location: Kristiansand, Norway

    Knut Sand Senior Member

    :confused:

    ok, can it be like: "But I have also seen engines with cooling intake on top (ehh bottom of, of course) of the cavitation plate, behind the propeller, the wash from the propeller doing the job for the impeller, don't recall the make though...."

    Then it just may be that it's the propeller wash that shall get the water circulating, helped by the vacuum behind the pipe going down again. one end pointing forwart against the propeller, the other end pointd aft. In a tank you'll probably will not get it to work.... Try to direct a water hose into the tube behind , do not put all the available waterpressure inside..... Or if yo blow (CAREFULLY) with an air pistol, can you feel it coming out from the other side of the pipe?

    Also, if it's one of them engines, they're not built for idle or out of gear running....

    btw; good luck.;)
     
  9. mabydick
    Joined: May 2009
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    mabydick New Member

    I have just spent the weekend comigg to the same conclusions you have! Bought a secondhand 5BS, starts fine but no water comes from the pee holes. I have the original owners manual which makes no mention at all of an impellor. I have looked everywhere and decided that if there was one then it would be put somewhere accessible for servicing/replacement. The manual DOES say that water should come out of the pee holes but ONLY WHEN IN FORWARD. I still can't get water out of them but do get exhaust.
    I spoke to a Yamaha service guy who says he thinks these are purely air cooled so took it out for a run yesterday (about 2 hours) with a careful eye on it. It got warm but like I'd expect a 2 stroke bike engine to. It didn't sieze!!
    I have a question though. At very low speeds (mooring) it cuts out. How do I adjust the tickover? (I'm a novice. This is my first outboard)
     

  10. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    The impeller should behind the plate under the propeller. It is turned by the propeller shaft. There are two bolts.
     
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