GENERAL
Beginning in 1983 Mercruiser introduced the R/MR/Alpha 1 series of sterndrive models. These units differed greatly from previous years not only in design but also in that the flywheel housing on the engine changed at this point. This creates one of the big break points customers should be familiar with when inquiring about re-powering older boats. Since the flywheel housing changed from 1982 to 1983, you cannot couple a new engine to a pre-1983 sterndrive unit as the rear engine mount spacing differs on the new engine and therefore will not match to the old style inner transom plate. The other difficulty is that the newer 14 inch flywheel utilize a larger coupler that prevents re-using the old flywheel housing on the new engine.

The R/MR/Alpha Generation 1 models began in 1983 and ran production through 1990. The serial numbers for these models ranged from 6225577 Thru 0D469858

The Alpha Generation 2 models were introduced in 1991 and are currently still in production. The Gen 2 units have been broken into several different serial number ranges as follows:
1991 thru 1995 - 0D469859 Thru 0F679999
1996 thru 1997 - 0F680000 Thru 0K999999
1998 and Up - 0L100040 And Up

GEAR RATIOS

A very common question raised when changing outdrives regards the gear ratio. Mercruiser made the following gear ratio changes several years ago in effort to develop s stronger gear combination.
What was a 1.50:1 thru 1995, in 1996 changed over to a 1.47:1
What was a 1.65:1 thru 1995, in 1996 changed over to a 1.62:1
What was a 1.84:1 thru 1995, in 1996 changed over to a 1.81:1
What was a 1.98:1 thru 1995, in 1996 changed over to a 1.94:1
In 1998 Mercruiser introduced the 2.0:1 gear ratio which has since replaced the 1.94:1

SHIFT LEVER

One noticeable difference between the Gen 1 & Gen 2 drives is the shift lever as shown in Figure 2. The old style brass shift lever will not engage in the Alpha Gen 2 transom assembly and therefore prevents installing a Gen 1 drive on the Gen 2 transom assembly.