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Thread: Yammie 50hp crankshaft rebuild question.....

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    Default Yammie 50hp crankshaft rebuild question.....

    After a little searching, I decided to send my little 3 cylinder pressed crank to Bill Bune in MN to have it disassembled so bearings could be replaced. Came back with bearings that do not have the rubberized outer races, but i figure a little 609 should take care of that. Bearings were unshielded though, and i am not sure about that. Original bearings had shields on top sides. What do you think?
    Thanks!

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    Shields are not needed except with grease lubrication and may prevent oil getting to the balls.

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

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    need a pic of it

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

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    Attachment 59638

    No photo, but hopefully I figured out how to attach diagram so you get the idea. I assume that they are there to prevent any trash (not sure where the trash would come from) from falling into the bearings. Original bearings can only receive lube from bottom. THe original bearings also had the "rubberized" stripes to prevent the outer raced from spinning. I feel pretty good that 609 Loctite retaining compound should take care of this, do you agree?

    Fast Fred, I just recently found this website, and it seems that you are one of the kings of these little motors. She's not a racer, just a fishing motor. But since its apart, I may try to get a few more HP if its a no brainer. I have several questions...If you answered even a few of them I would be most appreciative!

    What is safe max RPM to run 91 pump gas w/ 10% ethanol? Book says 5000-5500. Stock, she is propped to run about 5700 with boat empty now, 5400 boat loaded.

    Have learned that I can simply cut off a couple inches from tuner to gain a few....Stupid question, but is it gonna be a lot louder?

    Heads are stock with plugs in center (2006). Do you have a rough number that I can shave off that will put me in a range where I can still run crappy 91 pump gas and be reliable? I can recut squish band if needed, but If I can shave some off without it, that would be great.

    what is a good minimum squish clearance & good compression PSI for pump gas?

    Oiler - is it safe to leave it on there, or should I just start mixing fuel? I like the ease of the autolube, but am happy to get rid of it if it is problematic. Should I incorporate a "plug" to fill the void if I remove the shaft, or is a cover for the hole good enough?

    Sorry to bombard you....Have been asking these questions on the wrong website I think, and haven't got any real solid answers yet. I know that Hydrotec sells the head / tuner kit to get a quick 10 HP for these. If I can get that or close to that without spending a bunch, I would be just tickled.

    Thanks a million!!

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    i allways chucked the oiler, if ya can make a filler plug or leave the gear-shaft in side and put a cover over it. don't take the crank gear off. just clean any misalignment in the ports, leave the cyl alone, just the aluminum, 145psi is good for pump juice. squish band, you need to take a squish measurement to see were she is, you may not have to think about it............
    let it spin

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

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    i don't think i would cut the tuna, i would mill on the gasket end to get the squeeze closer..................... as long as you leave the muffler box alone she won't be loud.

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

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    nothing we have talked about really makes HP. a bevel on the top sill of the exhaust port with a set of 70hp carbs, then be makin some hp we could see and feel or just the bevel on the exhaust................

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

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    Quote Originally Posted by Fast Fred View Post
    i don't think i would cut the tuna, i would mill on the gasket end to get the squeeze closer..................... as long as you leave the muffler box alone she won't be loud.
    That is a surprise! I was thinking that was one of the first things folks did to these things. I haven't even pulled it out and looked at it yet, so I am not really sure what I will see. The Hydrotec tuner looks like it has a megaphone on the end. Would it be possible or smart to fab and weld something similar? Assuming I can weld onto the stock tuner?

    Does "gasket end" mean the top of the tuna, or are we talking about milling the head here? I gotta little yet to learn on the lingo about these modas..haha.

    Right now I am still in the cleaning and getting ready to build mode, and asking questions. Once I assemble it, I will definitely check deck height and squish.

    Here is a pic of the blow up and reason for the rebuild... I am not certain what happened here, kinda thinking a ring just let go. Wasn't much damage to holes, they are still measuring in spec, just a little close to the big end after a hone, so I just ordered std pistons. The old pistons measured round...really round... That surprised me, I always remembered pistons being a pain to get a real dimension cuz they aint really round, ya gotta mic em in the right spot. I definitely was hearing a little slapping before it blew up, and kinda figured it was coming for a while.
    Attachment 59639

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    Your attachments are not opening?
    " Three may keep a secret if two of them are dead" Ben Franklin
    " ------- well Doctor what have we got a Republic or Monarchy? A Republic he replies if you can keep it"
    Benjamin Franklin, 1787 Constitutional Convention, as recorded by signer James McHenry's in his diary at the Library of Congress

    Location: SW Orlando, Fl

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    tuna do not make HP, you can move the power band that you have by workin the tuna, short tuna will move the power band to the top of the range ( your hull will not like that) long tuna helps low and mid range of the curve. the top of the tuna where the gasket sits, there is a squeeze about 1 inch down, mill the gasket end to move the squeeze closer to the block, i've run the trumpet tuna, she ran well..........check the squish band, then cut the head, so not to pay for some thing you have to fix

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

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