Identifying Mercury V6s

[AxisMoto]

Today I took delivery of motor #1 for my project. It is a 1978 Black Max 175hp.

First, how can I tell if this is a 2.0 or 2.4? (I am pretty sure it is a 2.0, but who knows if someone already swapped powerheads...)

How can I determine the gear ratio for the lower unit? (Other than taking it apart and counting rotations transmitted through driveshaft).

If the lower unit has been changed, how can I tell if this is an early (preload type) or later gearcase?

Also, I hear talk of small hub and big hub props - is this the same as over exhaust versus thru exhaust, or are there different shaft sizes?

The prop I have is a thru exh cleaver, marked "CRICHARDS" and "7530" and "HH25160" - what can you tell me?

-David, AxisMoto

[Rickracer]

......count the revolutions till the propshaft makes exactly one revolution. It will be either two turns, 1.78, or 1.87. If the lower unit is the original one, it is probably a 2:1, and a pre-load pin type. :cool:

[larrry j]

2.0 liter, 3.125 bore 122 cubic in. 2.4 liter 3.375 bore 142 cubic in.

[northeastcat]

If the lower unit has been changed, how can I tell if this is an early (preload type) or later gearcase?


If it is a preload type it will have what looks like a little dowel sticking out above the splines at the top of the input shaft.