Vdrive Rebuild Question

[chpthril]

After dealing with a 1.5:1. Knowing the people running 2:1 aren’t struggling like I am with weight and elevation. And knowing all the manufacturers are going to these 1.76:1 and 2:1 drives on boats with this kind of weight, I’m convinced I need a 1.76 or 2:1..

I think you use the gearing to push the weight, and up the prop pitch, if needed to bring the revs down to where you want to be.


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Im my mind the magic is not in the gear ratio, its in the gear ratio allowing us to spin the larger wheels. So in your case, yes, up the ratio. In Sonics case, he's at the limit of prop diameter, so will a ratio change benefit?

Im not sure yet, and honestly, havent spent the brain power on it yet. At this point on a Friday evening, the forum probably doesnt want me to

[Zackdogg]

Im my mind the magic is not in the gear ratio, its in the gear ratio allowing us to spin the larger wheels. So in your case, yes, up the ratio. In Sonics case, he's at the limit of prop diameter, so will a ratio change benefit?

Im not sure yet, and honestly, havent spent the brain power on it yet. At this point on a Friday evening, the forum probably doesnt want me to

Haha!! I feel like Friday night is when all the real thinking gets done!!

Totally could be, and maybe that depends which prop is right for what he’s doing.. I wouldn’t recommend anyone run a 10.5” pitch, unless they absolutely have to.. if you’re moving all your weight, and hitting 40-45mph, with a 12” or higher, you’re probably running the right gears.. I’m sure someone way smarter than me knows these answers, as there is probably some kind of formula that you can run. For me, 100% pure guesswork, all based off my personal experience!


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[chpthril]

So here's my thinking: For the sake of the argument, lets leave prop slip out of it and just assume we have 0% and thats good. Lets also assume we have a 1:1 trans with 0% slip also.

Prop = 12 pitch
V-drive ratio = 1.5:1

So, in one prop shaft rotation, a 12 pitch prop travels 12" through the water. With a 1.5:1, the input shaft has traveled one and a half revolutions.

Same 12 pitch prop, but now a 1.75:1 ratio.

In the same prop rotation and distance, the input shaft has now traveled 1.75 revolutions. So about 17% more in the same given distance/time. This should = higher engine RPM, right?

Now, if we lower the prop pitch, we then complete a single revolution in a shorter distance/time

Going down in pitch is like increasing upstream power. So in my mind, I dont see an advantage to more torque multiplication in order to go down in additional pitch. If my thinking is correct, a ration change AND a drop in pitch is doubling down on an engine RPM increase. Now, this is not necessarily a bad thing, to increase RPM. Not enough data in rpm in here yet. RPM may not be too high, so room to go up under the target operating range. Maybe too low, and would benefit from an increase.

[Brianrzr]

I believe transmission gearing 2:1 and reducing prop pitch are two ways of effectively achieving the same thing. As chpthrl said boiled down to the basics is moving boat “X” distance with “Y” rotations of the engine. It is just the path you choose to do it. Now as far as prop diameter, I believe there is always slip, however the larger diameter “grabs” more water, effectively slipping less. Thereby reducing rpm. The centrifugal weight of the prop also has an effect, but I believe not nearly as much as the reduced slippage. As we all know, we are limited to the prop diameter because of the proximity to the hull. Seriously talking theory, increasing the strut length to allow a larger diameter prop, changes the props running angle with the hull. Like trimming down an I/O, it drives the bow down into the water. To counteract that, moving the existing point of the prop shaft from the hull forward will regain the shallower angle. I just love talking this theory stuff, I’ll get off my soapbox before I derail this thread any further.

[Aspidaso]

Beyond on the mind boggling math questions...…
I just rebuilt my RV-26D in July. I had a #10 gear with broken teeth. Here are what your looking at buying parts from Walter (I will spare you all the mafia speak some folks had on Walter's prices and business practices).
Repair Kit (seals, gaskets, bearings, u-joint repair kit) $ @480.55
#10 gear @ $455.00
#9B pinion gear @ $384.00
#42A oil pump @ $178.00
#42B pump end cap @ $114.00

The above includes every wearable part inside the drive except for shafts. I also purchased the "manual" which I later found online.

You mentioned getting Walter to do the rebuild and test for 1200, my guess is that price your getting new bearings and seals only (the repair kit).

You can also try contact this gentleman: Chris Jones cejones1956@gmail.com Tons of knowledge and he has rebuilt hundreds (I believe he is in South Carolina).
The rebuild is a easy process, an arbor/press available will make it go much smoother (I got away with a vise and a mallet).

Be happy to lend a hand if you need help.