Can i use a motorcycle engine?

Discussion in 'Boat Design' started by 65chill, Dec 3, 2008.

  1. Ilan Voyager
    Joined: May 2004
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    Ilan Voyager Senior Member

    A 450 Honda (I hope it's not the collection one DOHCT of the sixties...) it's a big and heavy, far too powerful. Isofar, to make a shaft, sprockets, chain, plus security items (mod of carbs) electric pump plus secondary gas tank (moto carbs are feeded by gravity) plus all the polyester work around and many other items, including lathe shop work will go farther than the 15 HP outboard...

    The small gain of retiring pinions will be upset by the work involved and the fact that a lot of motorcycle gear boxes need by design all the pinions to work.
     
  2. Tcubed
    Joined: Sep 2008
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    Tcubed Boat Designer

    I think i've answered my own question by thinking about. The honda engine if i remember correctly has the gear box and oil pan all in one piece so removing the transmission would mean a lot of expensive modifications.

    For a few pounds of weight it seems it is not worth it to remove. If i calculate the gear ratio for 4'th gear to work out the sprocket sizes i think i remove the transmission friction as i believe 4'th gear is one to one-direct.
     
  3. Tcubed
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    Tcubed Boat Designer

    I was thinking honda from the 80's pre 'rebel' or maybe even rebel 450.

    I've been searching the internet to see what the actual engine weighs, but no luck so far.

    The gravity feed is no big deal- A small tank is mounted high and gravity feeds. A larger tank has a hand pump near the driver. A few pumps every now and then to top up the little tank, you get the idea. Low tech and cheap is what i'm after, especially if it's for my own use.
     
  4. Frosty

    Frosty Previous Member

    So your going to fit another transmission to take the thrust?

    Why dont you use an engine only like a Harley or something off a cement mixer.

    If you fit the engine side ways to drive the shaft with the sprocket you will get side thrust on the shaft.

    You would be better off with a shaft drive engine.

    You would be even better off by looking for a little old marine engine at the boat yard. I strongly suggest it would be cheaper and probably work after all your efforts.

    What about an old jet ski unit, there must be thousands of em.
     
  5. Tcubed
    Joined: Sep 2008
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    Tcubed Boat Designer

    My mind is open but jet ski which sounds like a mutant mosquito and stinks of castor oil?...

    What i was envisaging is mount the thing sideways and a short chain down to a sprocket on the prop shaft. Thrust bearing on prop shaft, no thrust loads on engine. The sprocket on the prop shaft can go between two bearings to eliminate fatiguing the shaft from the lateral stress.

    Found this for planes http://thekneeslider.com/archives/2007/03/05/motorcycle-engine-powered-airplanes/

    Basically recaps what i was thinking that the engine has to run at considerably lower RPM's than peak performance or it won't last long. This implies a lower power to weight ratio.

    Question is just how much heavier does it end up being? This is what will determine feasibility. 15 HP yamaha outboard weighs 80 pounds.
    Honda CM 450 E (as an example) motorcycle weighs 400 pounds- what percentage of that is engine weight? If it's 30% then it means 120 pound engine which is feasible, extra 40 pounds will increase resistance around ten per cent, so i would still go the same speed as with the outboard at about a third of max output which should be okay 'cruise' speed for the engine.

    If it's 40% of 400 lbs or 160 pounds it starts to not be so attractive...

    I'm still trying to find the exact weight of the engine or one that is similar (about 40 HP to replace 15 HP outboard) but no luck so far.

    Frosty you say harleys engines have separate transmissions? This would be much better.
     
  6. Frosty

    Frosty Previous Member

    If you are trying to compare this to an outboard motor you might as well just stop right here. You will never ever beat the compact and efficient modern outboard motor .
     
  7. Tcubed
    Joined: Sep 2008
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    Tcubed Boat Designer

    I'm not trying to beat the outboard at its own game, but i am trying to see if there is a way of getting comparable motive power into the boat for less $ upfront.

    I'm reluctant to buy a used outboard because i know how most people here treat them. I have yet to see someone break in a new one, for example. Motorcyclists are much better at caring for their stuff i find (at least here) so i would not hesitate with a used motorcycle engine.
     
  8. Frosty

    Frosty Previous Member

    With the work you seem prepared to do on a motorcycle engine you will be far better overhauling an outboard.

    Again go to the boat yard Im sure you will get given one.

    The Honda 4 Hp 4 strokes are thrown away here for no other reason than carburettor probs. Ive picked one up once to have a look. If I squirted fuel in it ran but the fuel bowl post was rotted off so it needed a new carb which was the price of a new engine.

    I went to look for a second hand one and the guy at Suzuki shop gave me another whole engine that was exactly the same. he said "here take it"
     
  9. Tcubed
    Joined: Sep 2008
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    Tcubed Boat Designer

    I wish it were that way here. I'll keep my eyes open, but from what i've seen in Puerto Rico so far, outboards are used and misused till they expire on so many levels even the Cubans would not be able to revive them...
     
  10. rasorinc
    Joined: Nov 2007
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    Location: OREGON

    rasorinc Senior Member

    Here is the Tohatsu site. all 4 stroke. They make Nissan and now Mercury
    engines. Then search online for an internet dealer who sells inexpensive. The cost of shipping cannot be that great to your residence. You are going to a lot of work and have zero warranty and zero engineering. Failure of an engine 20 miles from home is not fun. http://www.tohatsu.com/ Stan
    Current economic times make for great prices. I quickly found a 4 hp for under a tho. new. When you add fuel pump, special exhaust and all the other stuff + welding you will be in it a lot of money and if I worked the internet I bet I could find one for $800.00
     
  11. Chris Bretter
    Joined: Nov 2008
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    Location: Durban

    Chris Bretter Zaphod

    Hi Ilan
    The outboard is nice but being able to flush the motors is a bit of a problem perhaps i am just wary of outboards.There are a few oriental air cooled diesel outboards but then you need a genset as well.
    Thanks for your input it all helps in finding an "ideal" setup
    Regards chris
     
  12. Ilan Voyager
    Joined: May 2004
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    Ilan Voyager Senior Member

    Frosty is right. Tcubed, it seems that you're not aware of the work and money involved in the marinisation of a 450 Honda, with all this custom hardware to make from scratch. Also it's too big, heavy and powerful for a very small boat designed for 15 HP. An industrial V twin Briggs or Subaru of 20 HP would be more rational, but you have to make all the transmission, shaft, calculate and adapt a propeller...

    A recent 15-20 HP outboard will be less expensive. Florida is full of such used engines to sell, some in very good shape and at good prices. In this very moment with the crisis, boat industry is almost starving you'll get low prices. The shipping won't kill you if you take a slow one.

    the http://thekneeslider.com/archives/2007/03/05/motorcycle-engine-powered-airplanes/ shows very expensive adaptations, big Harley Twin, 1200 BMW ouah, custom made transmissions by a shop at 100USD/hour, nice but I'm sure that the BMW costs more than 7000 USD, maybe close to a Rotax 908 at 12000 USD. I bet that the transmission alone is around 3000 bucks.

    We are far of the Metro, Geo or the old Subaru, bought 600 USD, and overhauled.

    Chris, forget the chinese diesels. Junk.

    Modern 4S outboards are nice pieces, nothing to do with the old capricious and smelly 2S. Easy to mantain. Flushing is nothing with an accessory you find everywhere for less than 20 bucks.
     
  13. Chris Bretter
    Joined: Nov 2008
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    Chris Bretter Zaphod

    I think you are right Outboards and a genset thanks Ilan
     
  14. Frosty

    Frosty Previous Member


  15. Chris Bretter
    Joined: Nov 2008
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    Location: Durban

    Chris Bretter Zaphod

    Hey Frosty now were talking english What angle can a Diesel run at.Modify the sump is no problem.This thai boat stuff is cool easy to fit in a wharram no universal joint just a reduction fwd and rev
     
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