What is my gear ratio ?

[amanphoto]

How do I find out what my gear ratio is? I have an Alpha 1 Gen 1 outdrive. I'm replacing it with another one. I want to make sure my ratios are the same. Mine came off a 350 - 5.7L - V8. Is there more then one ratio for V8's ?

I can't seam to find any number on the outside of the out drive. Please help.

 

[FreeBeeTony]

Re: What is my gear ratio ?

S/b 1.5:1.

 

[wire2]

Re: What is my gear ratio ?

Typical is 1.5:1 but I believe Merc has some at 1.47:1 (the difference is negligible)

 

[captk]

Re: What is my gear ratio ?

Pull the top cover off and count the teeth on both gears.

 

[jerryjerry05]

Re: What is my gear ratio ?

SBC v-8 is 1.50-1 The big block can have that or a 1.32-1 Most off a V-8 are the 1.5 to 1
Then you get into smaller motors with differnt ratios.1-98 1-65 and more.J

 

[John_S]

Re: What is my gear ratio ?

The "standard" ratio was 1.47 or 1.5 to 1, but there have always been optional choices to boat builders, or changed for high-altitude. For heavy boats, a 1.62 might have been installed to keep the prop pitch choices in the "sweet" spot. I am not familiar with Wellcraft Eclipse 233, but sounds like it may qualify as large/heavy. If you have a 2brl carb version of the 5.7L, migh also have the higher numeric ratio.

On genII drives the ratio is marked on decal and a code is stamped on the input shaft. Suspect same for gen I. Counting the teeth as suggested above is more accurate, and would cover the possibility of them being changed by a prior owner. You could get a "rough" idea by turning the engine over by hand. 1.5 engine revolutions should turn the prop 1 revolution (1.47/1.5 ratio).

 

[dvandsm64]

Re: What is my gear ratio ?

we have the 5.7 liter. our outdrive says 1;62 ,but even mechanic atmarina wasn't sure if it was rite or if it was just a replacememt housing with other gears.

 

[Eric 3.7LX Alpha 1]

Re: What is my gear ratio ?

Here is a stern drive ratio chart for different models and engine sizes.
From Miscelaneous Mercruiser Info in Adults Only stick- Alpha History:

 

[ziggy]

Re: What is my gear ratio ?

here was a way of determining gear ratio i got from someone here on iboats. can't remember who.

"Do all these steps in order.
1. Shut off the battery switch
2. Pull the spark plugs out of the engine.
3. Put the shifter in forward.
4. Turn the engine till the prop starts turning, continue turning till the timing mark is at TDC.
5. Put a mark on the prop hub and the drive housing that align with each other.
6. Turn the engine by hand while someone watches the marks on the prop, and count the revolutions the crankshaft makes to turn the prop 1 complete revolution.
7. If it took 1.5 revolutions of the crankshaft, then you have a drive ratio of 1.5:1 which is what is needed for a small block V8. (a 260)."

 

[amanphoto]

Re: What is my gear ratio ?

My boat weighs 4,000# dry.

I just wish there was a stamp on it. The drive I'm looking to replace it with is not on a boat. It just an outdrive sitting on a stand. But If I turn the input shaft by hand, the prop shaft should turn the 1.5 times.

 

[ziggy]

Re: What is my gear ratio ?

But If I turn the input shaft by hand, the prop shaft should turn the 1.5 times.

that's incorrect . other way around..

 

[Eric 3.7LX Alpha 1]

Re: What is my gear ratio ?

As mentioned above, there might be a letter stamped on the universal joint drive shaft, That letter signifies the ratio, if it hasn't been changed. The letter code is in that attachment I have above.

If you are buying used you should probably open the top cover and see the condition of the gears and top cover bearing. The teeth count on a 1.50:1 ratio is 22/20

 

[frank246]

Re: What is my gear ratio ?

My boat weighs 4,000# dry.

I just wish there was a stamp on it. The drive I'm looking to replace it with is not on a boat. It just an outdrive sitting on a stand. But If I turn the input shaft by hand, the prop shaft should turn the 1.5 times.

No...its the other way around.
If you turn the prop shaft 1 turn the input shaft turns 1.5, the gears reduce the prop turns they dont increase.
If you turn the input shaft the prop turns: 1 devided by 1.5= 0.66 turn or 237 deg.
Good luck!

 

[FreeBeeTony]

Re: What is my gear ratio ?

Go here.......http://www.mercstuff.com/drivegearratio.htm

 

[HT32BSX115]

Re: What is my gear ratio ?

No...its the other way around.
If you turn the prop shaft 1 turn the input shaft turns 1.5, the gears reduce the prop turns they dont increase.
If you turn the input shaft the prop turns: 1 devided by 1.5= 0.66 turn or 237 deg.
Good luck!

Yeah....Frank is right. (You wouldn't want the prop going 1.5 for every 1 engine turn!!)


It's pretty hard to turn the engine 1.62 turns while watching for the prop to go 1

it's a bit easier to turn the engine 16 turns and have someone count to 10
16/10=1.60.....or 15 turns and 10 turns etc.... (unless you have problems finding someone that cannot count to 10!!)

If you measure with a protractor on the engine (or input shaft) you could count 16 turns and then measure the 0.2 turn (72 degrees) for 1.62:1 etc.


If you're going to buy another drive and you're going to get a used one...you may end up in the same boat you're already in!! (pun intended)

You might consider an SEI (new) replacement drive.



Regards,


Rick

 

[John_S]

Re: What is my gear ratio ?

My boat weighs 4,000# dry.

I just wish there was a stamp on it. The drive I'm looking to replace it with is not on a boat. It just an outdrive sitting on a stand. But If I turn the input shaft by hand, the prop shaft should turn the 1.5 times.

Being it is on stand, might be better to pull cap and count teeth.

Rotating the drive shaft, dealing with the grease and u-joints, holding the shift lever engaged, and counting prop shaft turns, could be a bit "fun" by oneself. With two people, one turning the input shaft while the other is holding shift lever and observing/counting prop turns, would be allot easier.

As mentioned already, you have the rotation count reversed.

What letter is stamped on input shaft?

Assuming your current set-up produced the correct wot rpms, what prop and pitch were you using?

 

[ziggy]

Re: What is my gear ratio ?

apparently i can't read what i copied and pasted. thanks for correcting me in post #11. i corrected my statement..