Gear ratios

[blueskyracer]

Last year I ran a 14:15 gear foot on my D mod..This worked good except the 3/16 shear pins would not hold up..I plan to get a Bass foot with 1/4 shear pins for this year but I noticed the one under ratio is 16:17.. My question is what is the difference and why the different number? It is still one under, right..I do better building boats!

I gather the gear ratio is dictated by the torque and power band of the particular motor and prop used?

[ZUL8TR]

gear ratio

The 14:15 is 0.9333 and the 16:17 is 0.9412. The difference is about 0.8%. Both reduce the rpm of the prop but at different torque multipliers. The 16:17is a taller gear closer to 1:1 therefore there is less of a torque multiplier to the prop compasred to the 14:15 gears. Reversing the gear ratio we can see the torque multiplier. The 14:15 is 1/0.9333 = 1.0714 or a torque multiplier increase at the prop of about 7.1 %. The 16:17 is 1/0.9412 = 1.0625 or a multiplier of 6.25%. All else being equal the 16:17 gears will require less pitch or diameter to achieve the same RPM. Of course the engine torque and hp relation matters here as to what prop will work.

[Check Six]

Hey Mike,
The 16:17 and 14:15 are both one under so to speak. The 14:15 has a ratio of .933 to 1 and the 16:17 has a gear ratio of .941 to 1. So as you can see the 16:17 is closer to a 1 to 1. I doubt this is the reason your shear pin is breaking. Best of luck Eric

[blueskyracer]

That helps.. I just hope I dont have to start over with props but the 44 I have now has to much torque for 3/16's shear pins so I have to do something since I have tried every material for a 3/16 pin know to man..And Konig pins are 5mm so might as well go with 1/4 pins

So if my set up can handle the slight ratio changes with no RPM drop than I may gain some speed?

Thanks again

[ZUL8TR]

gear ratio

As I noted in post above there is a 0.8% difference. The same prop might just work with a relativly asmall difference and definately a place to start.
Question. With the different gears of 16:17 is the prop shaft the same diameter as the 14:15 gear shaft? If yes are you allowed to drill the pin hole to 1/4 diameter?

[blueskyracer]

As I noted in post above there is a 0.8% difference. The same prop might just work with a relativly asmall difference and definately a place to start.
Question. With the different gears of 16:17 is the prop shaft the same diameter as the 14:15 gear shaft? If yes are you allowed to drill the pin hole to 1/4 diameter?

The problem is that a 1/4 hole in a 9/16 shaft will not work..The bass foot has a 11/16 shaft so it comes with a 1/4 hole standard.

For some reason when I ordered my props I had them made with a 11/16 hole and used bushings..I guess I was lucky to do that to start with..

[seagull170]

Talk to your prop man about a second pin, just under the prop nut.

[STEVE FRENCH]

Also....check how loose prop is on shaft.....I have several props I need to bore and bush back cause they are TOO LOOSE on shaft!

[pro350hydro]

Mike,

There is no way that 4 banger will make enough power to break a 1/4" pin. Most of the 850 guys in our area use the Bass Foot and 1/4" pins and they usually don't break them. And the 850 makes way more power than those 4 bangers ever dreamed of. Not only more power, but they swing much larger wheels which adds to the stress on the pin. If I were you, I'd run the same pins as the 850 guys when you get your bass foot.

I know of several guys than run the smaller shaft on 4 bangers as well, and they aren't having the problems you are. Have you tried the Konny pins fron Steve Litzell? They hold up under the pro motors, should work fine on the 40/44. If you were breaking those pins, I'd say you may have a different problem like a sharp edge on the prop shaft at the pin hole which is helping "shear" the pin. I've had that happen before on a new unit. But that can be fixed easily with a file.

Good Luck

[pops67g]

Interesting prop shaft size

When you say your gearcase has a 9/16' shaft it sure is different from mine. I have five D Merc gearcases and all have an 11/16' shaft. I use 3/16' pins with no problems. The manufacturers of the Bass gearcase would have been really dumb if people switching from Merc to theirs had to change out all their props too.

[ddalton]

breaking pins

If you are using a modded 302 unit with a 9/16 shaft,are you using 11/16 props with bushings? or large hub 9/16 props...both these setups will shear pins easy!!! I had Lee make me some 11/16 shafts for my 302 units .never broke another pin !!! I run c mod (Yamato) D mod .(evinrude 60) (Merc 44)
Ran one on D Classic in 2010 also. Used very cheap 25 cents each clevis pins. Only use them once & disgaurded them Have also used other pins...from Brown tool & Machine I like these...use them only a few times & make shure they go in sme way round each time.
With the larger shaft the force from the prop has less leaverage on the pin. IMHO...DD

[Dave M]

Props

Mike,

Order a few new props. It will be needed. Different case size and hydrodynamics. As someone pointed out the aspect ratio is close. However there a TON more to it than a simple math formula.

[David_L6]

blueskyracer,

You have a bunch going on here.

You shouldn't be having problems with shear pins in a 44. There are people running 3/16" shear pins in 3 holers.

I think you were running a modified stock Yamato lower unit last year??? My preference for a 44 is a PRO Yamato hatchet lower unit with the shear pins that Steve Litzell sells.

Changing lower units and gear ratios.... Talk to your prop builder first. The Bass unit may or may not be wider than what you ran last year. That affects prop selection. You may be able to alter prop shaft height and use the same props you have. Again, talk to your prop builder. Then test.

[blueskyracer]

Dave the props I used last year were made for the one under Bass unit but then I could not afford one so hopefully they work even better this year with the unit they were made for. And both props were drilled for a 3/16 and then a second hole was put in it for 1/4 pins between the oposite two baldes. Buying the new foot will not leave any money for more props so I guess we will make ice cream out of Horse s***..

[ddalton]

Bushings!!!

So you were using a bushing!!! It gives no support to the shear pin..Just a Headache!!
The cheapest way to fix your problem is 11/16 shaft in Yamato lower unit.
I'm getting 3 more made when Lee does his next run of shafts.This will solve your problem!@!! & you can buy MORE PROPS with money saved!!!If you want you can also put 1/4" pin hole in one of these shafts. 9/16" shaft make no sense at all in anything bigger than a c stock or c mod ...DD