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Thread: Lower unit fun

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    JuniorRacer(VetMechanic) mercury400m's Avatar
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    Default Lower unit fun

    this is for 10-25hp lower units
    hey all im been toying with omc lowers l8ly and was really paying attention to the argument of running in reverse or forward/making it a direct drive no shifting. well what i discovered was the gears are actually the same just different bushing sizes on each end of the shaft the forward gear bushing is forced fit into so it would be some fun trying yo get it out if u had to. the gears are interchangeable with each other unless there is a pin at the back (only on older models) soo basically all you have to do is pin the either on the forward gear or reverse gear therefore decideing if you want LH or RH rotation. then after you decide what rotation you want you'd have to grind the teeth of the other gear you wouldn't be using =no other gear friction=) but you would keep it there for balence/stability in the lower unit. the clutch dog can stay there if wanted and probally best because then you gotta get rid of all the other shifting stuff. you can always leave it in forward for extra renforcement. The only hard part would be the drilling. i have some other lower units i will be testing this out on

    so basically you could run in reverse with a LH prop if you wanted to the gears would be fine(just think the gears are always turning and the clutch dog just "pins it/locks the gear to the shaft)


    the good times on the water are good but the best times are racing

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    Team Member Droll-l6's Avatar
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    Quote Originally Posted by mercury400m View Post
    this is for 10-25hp lower units
    **
    so basically you could run in reverse with a LH prop if you wanted to the gears would be fine(just think the gears are always turning and the clutch dog just "pins it/locks the gear to the shaft)
    The gear will work just fine, but how about the bearings ?? usually the forward gear got a nice big bearing behind it to support the forward thrust, but the reverse gear only got a simple bushing.

    The big question would be the bearing support for the prop shaft( forward thrust ), bearing on the forward gear or somehow directly connected to the shaft .

    My guess..It will work... some hours.....then....


    Arne Kjetil
    My engines :
    Mercury TII, next project
    Johnson V4m-10s 90 hp 1964,from the prosess.
    Mercury 1400 1972 ,Rebuilding a Tower

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    JuniorRacer(VetMechanic) mercury400m's Avatar
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    Default

    ill post some pics when i get home (im at school right now) but the forward and reverse gears are technically the same. the only issue would be pining the gear but not the bearing. you could pin the bearing but that would be absoulty pointless and kinda dumb lol. but the good thing is the bearing can come off the gear ... if you could cut a little channel in the bearing bushing and pin the gear directly it would work great or drill a hole in the gear and put a pin in just a little smaller than the diameter of the bearing and the slide the busing on topid put a little goop in to help from making th epin slide around. it all depends if you want LH or RH rotation. that bushing senario would be for regular RH rotation

    this may seem like a dumb question but why are racing props all LH rotation as a oppsed to RH rotation?? i just never was told why....

    BUT if you wanted LH rotation it would be way easier. the reverse gear doesn't have a bushing but a cast in big ring opposite to the gear for stability so in this case all you gotta do is grind forwards gears off and drill a hole right through the gear and shaft (get my friend that works at a machine shop to do that for me) and then press fit a roll pin through it. therefore making it a LH rotation direct drive.

    the only issue with the bearing would be if you wanted to make it a RH rotation direct drive..... which who wants that if there going to put that much efffort in to it just to achive a little less reverse gear fricton. besides its easier to make LH direct drive apposed to RH.

    jeff said hes done this b4 mabee he'll chime in and correct me if im wrong

    note: the bushing already have holes in the for oiling aswell as the gears and the wouldn't need them if there not rotating anyways.
    Last edited by mercury400m; 06-05-2007 at 10:58 AM. Reason: fergot sumtin


    the good times on the water are good but the best times are racing

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    JuniorRacer(VetMechanic) mercury400m's Avatar
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    here are the gears in the lower
    Name:  18hp lower4.JPG
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    heres the two gears
    (left gear is the forward gear and the right gear is reverse)
    Name:  18hp lower5.JPG
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    heres a pic of my shop in my garge(put it up just for fun )
    Name:  shop1.JPG
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Size:  61.5 KB


    the good times on the water are good but the best times are racing

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    Default backwards?

    Quote Originally Posted by Droll-l6 View Post
    The gear will work just fine, but how about the bearings ?? usually the forward gear got a nice big bearing behind it to support the forward thrust, but the reverse gear only got a simple bushing.

    The big question would be the bearing support for the prop shaft( forward thrust ), bearing on the forward gear or somehow directly connected to the shaft .

    My guess..It will work... some hours.....then....


    Arne Kjetil
    How about just running motor the other way and still use forward gear forleft hand rotation?
    RichardKCMo

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    That Tohatsu guy. jeff55vDSH's Avatar
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    Default rotation

    The location of the drive gear in relation to the pinion gear decides driveshaft rotation.
    When there's no gearshifting to worry about, it just plain makes more mechanical sense to have the driveshaft gear behind the pinion gear.
    I think you're fighting a losing battle with this 18 lower unit. If you can't afford, or find a Yamato lower unit, perhaps you should look for a KG-7 lower unit? It's smaller than an 18hp and the right rotation.
    Jeff Yungen

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    JuniorRacer(VetMechanic) mercury400m's Avatar
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    lol im just messin round jeff i had a spare 15 that will never be used so i decided to have some fun with it. u said u pinned a few 18's in ur day


    the good times on the water are good but the best times are racing

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    Default That's a plan!!

    Quote Originally Posted by jeff55vDSH View Post
    The location of the drive gear in relation to the pinion gear decides driveshaft rotation.
    When there's no gearshifting to worry about, it just plain makes more mechanical sense to have the driveshaft gear behind the pinion gear.
    I think you're fighting a losing battle with this 18 lower unit. If you can't afford, or find a Yamato lower unit, perhaps you should look for a KG-7 lower unit? It's smaller than an 18hp and the right rotation.
    Jeff, that's the thing , i've picked up 3 for some projects down the road.
    I always look on ebay.
    RichardKCMo

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    That Tohatsu guy. jeff55vDSH's Avatar
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    Default wasn't me...

    Quote Originally Posted by mercury400m View Post
    lol im just messin round jeff i had a spare 15 that will never be used so i decided to have some fun with it. u said u pinned a few 18's in ur day
    Hey, no problem. May as well give it a try. Hope it works. Sorry if I came off as a naysayer.
    Lemme know if you need any parts. I probably still have a few OMC fishing LU's around.
    BTW, it was johnsonm50 who talked about pinning a few LU's I think. (Over at HR) I stated over at HR that I never raced OMC's.
    Jeff Yungen

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    JuniorRacer(VetMechanic) mercury400m's Avatar
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    hey np jeff every one has there own opinion thats wat these forums are for if ur a na say hey ill live with it lol

    geez lol i know too many people lol johnsonm50 was the one lol srrys

    hmm parts.. u wouldn't have say a forward gear would you that would fit an 18 ... if u did maybee u could stuff it in with the tower


    the good times on the water are good but the best times are racing

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