NRG 140cc twin engine in progress.

Discussion in 'Scooter Projects' started by MARSH, Sep 15, 2013.

  1. Merlin

    Merlin Old School Biker

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    The best sounding two-strokes of all, the Kawasaki KH triples, all had three pipes, one per cy;linder. The sound they made when the bike was in the power band was glorious.
     
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  2. MARSH

    MARSH Whooooo!

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    And a beautiful plume of smoke all the way down the road!
     
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  3. Stevep

    Stevep Well-Known Member

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    just another thought on the two into one theory, (started something here didn't I !!!)
    Reading everything you all put here, and looking at stuff on the interweb, I think it will work.
    With the two barrels being timed at 180 degrees apart, the exhaust gas pulses are being produced at different times, thereby leaving a (theoretical) gap between each pulse through the exhaust. You should in effect only have twice the gases coming out the end can, and no build-up pressure of gases being caused in the body of the pipe. The only place they could start to collide is at the exit point, the end can, if it's too small a hole.

    Alternatively, you could put one out each side of the bike
    Just throwing things in the air to see what sticks
     
  4. GazD

    GazD Active Member

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    this might be the reason it doesn't work very well steve

    [​IMG]
     
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  5. Stevep

    Stevep Well-Known Member

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    5,895
    exactly what i said. Nice diagram by the way. Gases colliding at the exit point.
     
  6. MARSH

    MARSH Whooooo!

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    If I did that everyone would be building one!;)
     
  7. GazD

    GazD Active Member

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    you say that like its a bad thing
     
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  8. Merlin

    Merlin Old School Biker

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  9. MARSH

    MARSH Whooooo!

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    Close but no cigar, I used that joint and gave Dave that very same splined coupling, It did'nt work for me in a 250 and definitely did'nt work on a 350! My twin stand's me at around a £1000 so far and far easier making this than a 250cc.
     
  10. mrhappy

    mrhappy Member

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    .
     
    Last edited: Jun 25, 2023
  11. MARSH

    MARSH Whooooo!

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    What makes you say that?
     
  12. Stevep

    Stevep Well-Known Member

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    I think he's pissed because you wont share the secret;)
     
  13. Stevep

    Stevep Well-Known Member

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    I'm just thinking Marsh, with the engine being the width that it now is, it's gonna be a bitch to centralise in the frame innit?
     
  14. Merlin

    Merlin Old School Biker

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    OK, so how about one crank end being slotted, with the other keyed to match the slot, then the whole joint fitted with a shrunk-on steel sleeve, to reinforce the joint and increase the diameter? You could even shrink a bearing over that type of joint if the case had a housing for it. If slots are part of the answer, then how about large Woodruff key slots in the cranks, with a slotted sleeve to locate them?

    Another possibility is a Hook joint that would allow for slight mis-alignment, like a constant velocity joint on a car driveshaft. I think that may work out to be too long for the cases though.

    Welding the sleeve might introduce imbalances and distortion, so although welding a sleeve over the joint would work, the double crank would need to be balanced afterwards.

    I'm also thinking about maintenance, as the cases may need to be taken apart for rebuilding work, so welding the cranks would prevent any maintenance, so I doubt it's that either.

    I've worked around engineering shops during my time as a metalworking fluid specialist at Shell, so I'm thinking around other ways to join those cranks. A sleeve-and-pin approach wouldn't be as strong as the splined shaft so that's a no-go. It's an interesting puzzle to solve...

    The Woodruff Key approach seems the most likely to me at the moment.
     
  15. MARSH

    MARSH Whooooo!

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    Mr Merlin, you are on the right track and very close! (In box me if you figure it out :D) Mr Stevep, I'm leaving the engine in it's original position in the frame, it should just fit within the frame rails,the old 250 engine I spaced the rear wheel by 70mm to move it over. And mrhappy, after spending maybe £2500 ish and 3 years of trying many different types of joint, some lasting 1/2 hour before they fu*ked up just to tell you how it's done, err think again! Why not get your 3000 euro's out (+ barrels+carbs+pipes+engine) and by a kit from Italy like Pm have done!
     
  16. GazD

    GazD Active Member

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    fair enough mate,time and money and all that

    is this the kit your on about

    [​IMG]
     
  17. MARSH

    MARSH Whooooo!

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    Yes, that's the kit, and guess what? they don't show you how the joint is made!! I'd love one of these kit's but the wife say's NO!
     
  18. GazD

    GazD Active Member

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    yeah crazy prices,maybe they joined them like the rd350 cranks

    [​IMG]
    [​IMG]
     
  19. Merlin

    Merlin Old School Biker

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    I would just cut large Woodruff key slots into the two crank ends and use a thick sleeve that is also slotted right through to take both keys. A larger key would handle the stress better and would still allow for disassembly. The flywheel stays on with a Woodruff key and as long as the slotted shaft would cover both keys with some overlap, then they shouldn't separate and it would be easy to do from an engineering point of view. If a small section was left unslotted in the centre of the sleeve it would self-centre on the cranks. The shafts don'e need a taper like the flywheel does.

    One other way is to fit sprockets to splines cut on each shaft and use a length of duplex chain to join the two sprockets together.
     
  20. turbovetto

    turbovetto Well-Known Member

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    tweaked ovetto

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