Wanted: Bravo 3 sterndrive

[Gareth231]

Bravo 3 X sterndrive wanted 1:81 ratio

Message me if you can help

[beamishken]

Originally Posted by Gareth231

Bravo 3 X sterndrive wanted 1:81 ratio

Message me if you can help

My pal has a 1.81 bravo 2 if your on a single engine its a straight swap and more reliable

[Gareth231]

Originally Posted by beamishken

My pal has a 1.81 bravo 2 if your on a single engine its a straight swap and more reliable

Thanks for the offer but it needs to be a bravo 3

[beamishken]

Whats up with your old drive?

[Gareth231]

Originally Posted by beamishken

Whats up with your old drive?

Its the wrong ratio + lower unit is badly corroded

[GuyC]

That'll be those aluminium anodes

[beamishken]

Originally Posted by Gareth231

Its the wrong ratio + lower unit is badly corroded

Ah ok good reason to switch to a b2 they don't rot half as bad as a b3 [emoji6]

Could you get away with just a lower unit? What ratio do you currently have?

[Gareth231]

Originally Posted by beamishken

Ah ok good reason to switch to a b2 they don't rot half as bad as a b3 [emoji6]

Could you get away with just a lower unit? What ratio do you currently have?

The boat is being re powered petrol to a diesel, current ratio is 2:1.

Engine being fitted is a yanmar 6lp-dte 260hp from research 1:81 seems the ratio required.

Lower unit could possibly be replaced on its own but I have been told it needs to be a x drive due to the high torque of a diesel

[beamishken]

your 2:1will work if propped correctly you could change the lower unit but you'd still be 2:1 as the ratio change is done in the top end from 2.0 to 1.81:2. you could also fit a 1.65:1 ratio lower to your 2:1 upper which would give you a 1.65 drive.
The x drive top end is supposed to be stronger but the yanmars will still smash them without careful application of the throttle. I once bought a petrol drive that had done 1600 hours behind a 315hp 6lp and it was fine. Depends how careful you are with it I guess.

To be honest the b3 is the least reliable of all the bravos. depending on the boat I wouldnt discount a bravo 1 or bravo 11 both are usually cheaper, there more reliable and rot considerably less

[GuyC]

Originally Posted by beamishken

you could also fit a 1.65:1 ratio lower to your 2:1 upper which would give you a 1.65 drive.

I don't understand this I'm afraid.

If the input shaft at the top of the stern drive is doing a 1000 RPM and the top bevel gear is 2:1, then the shaft between the upper and lower bevel gear would be travelling at 500 RPM. If the bottom bevel gear is 1.65:1, then isn't the output shaft at the bottom travelling at 303 RPM which is an overall ratio of 3.3.

Do you not just multiply the ratios?

[beamishken]

Originally Posted by GuyC

I don't understand this I'm afraid.

If the input shaft at the top of the stern drive is doing a 1000 RPM and the top bevel gear is 2:1, then the shaft between the upper and lower bevel gear would be travelling at 500 RPM. If the bottom bevel gear is 1.65:1, then isn't the output shaft at the bottom travelling at 303 RPM which is an overall ratio of 3.3.

Do you not just multiply the ratios?

The overall ratio is a combination of upper & lower reductions. to achieve the ratio changes mercruiser use a selection of upper and lower gear sets to obtain the final overall ratio. IE a 1.65 ratio uses the same top gears as a 2.0 while a 1.81 uses the same lower as a 2.0 and changes the top gearset. Its just a case of knowing which top gears matched with which lowers give what overall ratio

[GuyC]

OK thanks