alpha leg

[dento29]

Hi all, can anyone see a reason why i can't fit a alpha leg from a 3.0 engine to a 5.0l engine?

Many thanks

 

[45Auto]

Re: alpha leg

It'll fit fine. The gear ratio will be wrong, the 5.0 V8 has much more torque so the 5.0 outdrive is geared higher. You'll have to do something with a new propellor of much lower pitch (which will generally be much less efficient for your motor, which is why it has a different gear ratio to begin with .....) to try to get the max RPM back up where it needs to be for the 3.0.

 

[bigskiohio]

Re: alpha leg

he is right but it will work , there has to be somebody that has done this that will tell you results. it will get you on the water.

 

[TilliamWe]

Re: alpha leg

As stated above... a 3.0 should be a 2.0 to 1 ratio, where the 5.0 is at the very most, likely a 1.65. So you would end up with an odd gear ratio, and you'd need a higher pitch prop. It can be done though. My father used his 1.81 ratio drive from a 4.3 when he changed to a 5.7. But he needed like a 27p prop, which he didn't have, and are not all that common. Later, he put a different lower unit on and ended up with like a 1.65 ratio. He was able to use a 25p prop then. Worked just fine.

 

[dento29]

Re: alpha leg

Thanks for the reply.
So in terms of pitch, would you say less or more (ratio is 1.98:1) and any long term damage from this?

 

[dubs283]

Re: alpha leg

So in terms of pitch, would you say less or more (ratio is 1.98:1) and any long term damage from this?

pitch? hard to say, depends on the boat

long term damage, you bet. mercruiser makes different gear ratios for a reason

you're either gonna lug or over-rev the motor and destroy it or smoke the drive unit

putting a different prop on may work in a pinch, but over the long run, the drive is still gonna be spinning the same regardless of prop pitch

your best bet is to order a new upper gear set for the drive, shim it properly and then you know your set-up is correct. why guess?

 

[dento29]

Re: alpha leg

Thanks for all your help, what a great forum! ..just want her back on the water and being in the uk-not alot of mercruiser legs come up so if i can make it work then great!

 

[TilliamWe]

Re: alpha leg

You know that SEI lower units are only about $795, brand new, with three year warranties? They are sold right here on iboats.

 

[bigskiohio]

Re: alpha leg

i thought the lower is where the ratio is made

 

[mkast]

Re: alpha leg

i thought the lower is where the ratio is made

Upper.

 

[TilliamWe]

Re: alpha leg

i thought the lower is where the ratio is made

And I thought it was a combination of the two?

 

[cooter2506]

Re: alpha leg

I thought all the uppers were the same and the lower is where the ratio change was.

 

[WAVENBYE2]

Re: alpha leg

On my Alpha One drive the ratio is labeled on the upper unit, don't know if that means anything.

 

[TilliamWe]

Re: alpha leg

On my Alpha One drive the ratio is labeled on the upper unit, don't know if that means anything.

No. It's just where they stamp the numbers.

 

[bigskiohio]

Re: alpha leg

i still say lower.