Lower unit fun

[mercury400m]

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)

[Droll-l6]

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....:eek:


Arne Kjetil

[mercury400m]

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:rolleyes: and kinda dumb lol. but the good thing is the bearing can come off the gear:eek: ... 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.:D

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.

[mercury400m]

here are the gears in the lower
16521
heres the two gears
(left gear is the forward gear and the right gear is reverse)
16522
heres a pic of my shop in my garge(put it up just for fun:) )
16523

[RichardKCMo]

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....:eek:


Arne Kjetil

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

[jeff55vDSH]

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.
:)

[mercury400m]

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 :confused:

[RichardKCMo]

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

[jeff55vDSH]

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 :confused:

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. :)

[mercury400m]

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:D

[JohnsonM50]

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:D


Yup that was me, If you look into my posts here on BRF youll probly find that I wrote about the nearly identical next size up OMC lower. Conclusion... alot of improvement is possible but at that gear ratio in relation to props available,,, youll need a foot. With an AB 1 to 1 under an OMC 18 Ive seen a C or D hydro with a lite driver do upper 40s. :D No matter what you do to the OMC foot an 18 wont do that.

[JohnsonM50]

here are the gears in the lower
16521
heres the two gears
(left gear is the forward gear and the right gear is reverse)
16522
heres a pic of my shop in my garge(put it up just for fun:) )
16523
When this is in reverse the propshaft is pushing forward and the gearlash is trying to spread the gears pushing the R gear against the bearing head [$115 new]. The location of the bearing head is indexed with a small pin. Granted these gears are TUFF its the surrounding parts. Notice the engieering of forward gear thrust management. If you go the reverse.. post your results here for posterity lol

[jeff55vDSH]

Here ya go Christian. This is what you need. Happy bidding! :)

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=160165200176

I hope ya win it! It would be great to read about you fabricating this onto some kind of fun/racin' motor!

[goldenshinner]

im currious also if you get this to work. as i am also interested in trying such a modification. what about simply using the left hand rotation prop and engaging the reverse instead of forward? with all the original gears and bushings untouched the power transfer should be the same roughly.

[JohnsonM50]

im currious also if you get this to work. as i am also interested in trying such a modification. what about simply using the left hand rotation prop and engaging the reverse instead of forward? with all the original gears and bushings untouched the power transfer should be the same roughly.
This exact idea has been tossed around on several boards inc. here, it would work for awhile but if you look at the lower unit youll see that the F gear is far more beefed up than the R gear. Look for postsabout it and please post results if you do it.

[Skoontz]

On a simliar topic, there is a guy down south who makes mud motors he calls 4x4 outboards. They all run air cooled engines, (Honda, Briggs, Kohler, Kashwacki) and use a long stick extending into the water from the transom. Prices start at $1,800 to $3,000 but if you look at the pics, you may bea able to take a junk yard lawn mower bock and concoct something alot cheaper and more effectively than what you are attempting here.....