Thanks Thanks:  0
Page 1 of 4 1234 LastLast
Results 1 to 10 of 37

Thread: yamaha 70 ces

  1. #1
    Team Member
    Join Date
    Jan 2012
    Posts
    30
    Post Thanks / Like

    Default yamaha 70 ces

    I want to get the flywheel lightend, and have a few questions about it.
    It has 3 rivets in it, when i drill these out will it seperate the ring/gear from the flywheel?
    Also my engine has the 6j2 pistons in it, as I have read these are not the best.
    How long will these last? Engine has not much hours...

    Engine will be ported and 90hp carbs.





    Grt

  2. #2
    Team Member
    Join Date
    Jan 2012
    Posts
    30
    Post Thanks / Like

    Default

    Or if someone can offer me a link to an exploded view of the flywheel...

  3. #3
    Team Member
    Join Date
    Jan 2012
    Posts
    30
    Post Thanks / Like

    Default

    To me it Looks like the rivets holds the starter gear in place...
    If you have experience with these motors feel free to post...

    Im planning to drill the rivets out, machine the starter gear thinner myself.
    Then let someone cnc machine circular forms in it to lighten it some more.
    Make the rivets self and press it back togheter.

  4. #4
    phillnjack
    Guest

    Default

    so your just going to make it a 90hp then ?
    isnt it just the carbs that is the difference in the engines ?

    Dont forget when you lighten the flywheel you will need to re-balance with the starter ring back in place.
    a lighter flywheel will cause a lot of differences, especially at slower speeds.
    if its purely a drag race engine then fine, if you use it for recreation its not a good idea at all.
    It would be cheaper for the factory to sell the engine with a lighter flywheel, !!!!!!!!!!!!

    i can never understand why people buy new engines that are just big engines with small carbs.
    when secondhand yes its fine as the engine will probably never have been tested to its normal limits.

    phill

  5. #5
    FFX-61
    Join Date
    Aug 2005
    Location
    Stellwagan Ledges
    Posts
    1,389
    Post Thanks / Like

    Default

    the starter ring is pressed on the hub, the rivets hold the rope ring on . weld the crank or lose the press. the stock high ring pistons are ok, i was not able to get new rings for that piston, once the rings wore out i'd change out the pistons. 17-18deg MAX advance, pull to 7800rpms, not the same as a 90hp powerhead.

    Part one of "Secrets of the OMC Mod 50" : http://www.boatracingfacts.com/forums/showthread.php?t=2052

  6. #6
    Team Member
    Join Date
    Jan 2012
    Posts
    30
    Post Thanks / Like

    Default

    Got the flywheel back today, shaved 1.2kg of the total wheight.
    If you want, it can be more... tomorrow i will balance it.
    Also mounted the 90hp carbs on the intake and matched them together.
    Soon i will start the porting work.









  7. #7
    FFX-61
    Join Date
    Aug 2005
    Location
    Stellwagan Ledges
    Posts
    1,389
    Post Thanks / Like

    Default

    brush out the 70 intake to fit the 90 carb base gasket, i'd chuck the choke plates and the reed stops, you will need to make some room for that bottom carb bowl in the tray

    Part one of "Secrets of the OMC Mod 50" : http://www.boatracingfacts.com/forums/showthread.php?t=2052

  8. #8
    Team Member
    Join Date
    Jan 2012
    Posts
    30
    Post Thanks / Like

    Default

    slowly building further on the engine.
    Made a portmap, squish, cc of each cilinder. Determind the height of the ports, compression ratio and now im starting to shave the cilinderhead.
    It is a strange cilinderhead, combustion chamber off center.
    Don't know the right words to explain bt the ones who are familiar with these engines will know what i mean.
    How did you make the shape of the piston dome back in correct place?
    I was planning to make center on the mill using the outskirts of the waterjacket.
    But the shape is out center.
    have the cutting tool as good as possible in the center now, but i'm curious about other experiences.

    The 70hp intake is also mod to fit the 90hp carbs.
    Tray will be the last thing

  9. #9
    Team Member Roflhat's Avatar
    Join Date
    Jul 2011
    Location
    Scotland
    Posts
    166
    Post Thanks / Like

    Default

    What did you do to make the carbs fit? On mine the throttle roller is on the middle carb on the 90 carbs but the bottom one on the 70. Did you just swap the middle and bottom carbs and the chokes?

  10. #10
    Team Member
    Join Date
    Jun 2005
    Location
    Eastern PA
    Posts
    661
    Post Thanks / Like

    Default

    Glad I'm not sitting a few feet away from that potential grenade!

    Jeff
    "We live at the bottom of an ocean of air." - General Marvage Slatington

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. 40/50 yamaha tiller on 30 yamaha??????
    By BRzuki in forum Technical Discussion
    Replies: 7
    Last Post: 09-06-2014, 05:58 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •