Mercruiser Alpha 1 gear ratio

[Valv]

I purchased an used Alpha 1 upper drive for my project boat. Appears it has 1.98 gear ratio (was on a 4 cyl 140hp) and I have to install it on a V8. It appears V8 needs a 1.50 ratio. If I leave ratio this way and work on prop pitch and size will it be ok ?<br />Also gears are 20/24 (I assume teeth) for 1.98, and 20/22 for 1.50. I should replace only one gear (from 24 to 22) right ?<br /><br />Any info will be appreciated since replacing gears is not cheap and if I can get away from it....I'll be happier.<br /><br />Thanks.<br /><br />Val

 

[ODDD1]

Re: Mercruiser Alpha 1 gear ratio

Valv, I have seen this particular combo done in the past...it will work, but not as efficiently as the 1.50 ratio........whatever you had for pitch on the prop, add 4 more inches,at least.....if this is a large, heavy, single screw boat,dont expect the upper gear set to last too long.....they were designed to handle the power from a 4 cyl motor, not a V-8.....you cannot replace just one gear, the sets are matched and mixing ratios, the teeth will not mesh........bsides, just tossing a gear in the case will get you nowhere but in costly trouble.....the gears must be shimmed for depth in the case and rolling torque set on the bearing packs as well....or, you buy another drive...

 

[Valv]

Re: Mercruiser Alpha 1 gear ratio

ODDD1 thank you for the reply, that's exactly what I didn't want to hear. I am restoring a 26' SeaRay, I found a Mercruiser 327 motor alone, then this alpha from a scrapped boat with a 140hp. I assume my V8 is around 230/250 hp, adding 100hp more to unit without changing ratio is an invitation to troubles on water.<br />Is changing gears very tricky ? I am a somehow good mechanic, even if not a professionist, I rebuild motors here and there, but never worked on lower units or drives.<br /><br />Thanks again.<br /><br />Val