Lower unit gear ratio

tlh 178

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have a 2001 135 opti DFI, serial #OT274600 and wonder how you tell what the gear ratio on the lower unit. they make 3 different ratio for clockwise rotation. i looked for a stamping number on lower unit, but didn't notice anything!
 
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Alumarine

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I'm not sure if you can access the flywheel easily on that model.

If you can put it in gear and turn the flywheel by hand then you can count the number of complete and partial revolutions of the motor to turn the prop one complete revolution.

If that makes sense or is even possible with that model.
 

tlh 178

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yes i can access the flywheel. i don't have the lower unit on right now. i found that my driveshaft was eating my impeller and melting the upper part of the impeller to upper water pump. the driveshaft is all scratched up and has a groove in it. i'm looking at my options on to buy a new driveshaft and repair whatever i might find wrong or just buy a whole new lower unit and be done with it. if i bought a new L.U. would it matter what the ratio is?
 

jimmbo

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Well if you replace the driveshaft you will have an chance to count the teeth on the gear and pinion and then you will know. If you replace the whole lower unit then yes, the ratio does matter as you can continue using your existing props. A different ratio will require different pitches to get close to the previous rpms. even then there may be a difference in Holeshot and Acceleration. Where exactly is this groove and how deep is it? A good picture(in focus, good lighting, and reasonable resolution) can be very informative
 

tlh 178

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thanks for the reply guys. best i can tell the groove somewhere above the impeller and the top cover. i get some pics in a bit, cell phone is dead! i think the needle bearing is out of specs, about to go! i can wiggle it a bit, side to side about a 1mm.
 
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Alumarine

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If the lower unit is off it's even easier than turning the flywheel.
Just rotate the driveshaft.
 

tlh 178

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No Title

the groove is just above the key slot and as you can see, 3/4 inch above is rubbing also.
 

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tlh 178

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If the lower unit is off it's even easier than turning the flywheel.
Just rotate the driveshaft.

which way would i turn the shift shaft, clockwise or counter, as its in neutral?
 

Alumarine

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which way would i turn the shift shaft, clockwise or counter, as its in neutral?

Either way will be fine.It won't matter if it's in forward or reverse.
It might go into gear easier if you turn the drive shaft at the same time.
 

tlh 178

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after more reading of the manual on boatinfo, i was able to find the answer. has 200.1 ratio and 14/28 teeth. thanks jimmbo and marc c for your input and advice!
 

Faztbullet

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i think the needle bearing is out of specs, about to go! i can wiggle it a bit, side to side about a 1mm

That's 100% normal if your not pulling up on driveshaft when checking, This driveshaft use a upside down bearing and is preloaded by the gears when running. You can take a file and remove that transfer from impeller cup housing. Better check the water dump holes in echaust plate as this can cause water pump housing to warp and rub shaft and can cause carrier seal failure along with melting hub in props with rubber hubs.
 

tlh 178

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thank for your advice fb, now i'm thinking about just filing driveshaft and saving alot of money. if i were to fix this, what would be the steps to add a working temp gauge . my boat does not have one? there is a blank water outlet coming off motor, not sure if that would read temps or is just made for pressure reading?
 

jimmbo

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That blank outlet is where the fitting for the water pressure gauge is attached. Mercury never offered a temp gauge for those engines. There may be an aftermarket model but I am not aware of it
 

tlh 178

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Jul 14, 2013
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That's 100% normal if your not pulling up on driveshaft when checking, This driveshaft use a upside down bearing and is preloaded by the gears when running. You can take a file and remove that transfer from impeller cup housing. Better check the water dump holes in echaust plate as this can cause water pump housing to warp and rub shaft and can cause carrier seal failure along with melting hub in props with rubber hubs.

do you have to pull powerhead to check water dump holes. i'm not sure how to check this.
 
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