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The Mercruiser Stern Drive

Gen II Mercruiser

10-Hour Break-In:
On all new or rebuilt drives there is a 10-hour break-in procedure. Avoid full throttle starts. DO NOT operate at one constant speed for extended periods of time. DO NOT exceed 75% of full throttle during the first 5 hours. During the next 5 hours, operate at intermittent full throttle. The drive unit should be shifted into forward gear a minimum of 10 times during break-in, and operated at moderate RPM after each shift. Following the 10-hour break-in the drive lube requires changing when 20 hours on the drive is reached. After this time the normal maintenance schedule for lube change can be followed.
Drive Model Year Index:
A reference chart for all Mercruiser stern drives, including Alpha drives, Bravo drives, and TRS drives. The chart lists model, year, and serial number. Stern Drive Index
Fluid Capacity:
ALPHA                  approx 39.2 oz (1160 ml)        w/reservoir approx 64 oz (1892 ml)
BRAVO I               w/reservoir approx 2.8 qts (2.65 l)
BRAVO II              w/reservoir approx 3.2 qts (3.03 l)
BRAVO III             w/reservoir approx 3 qts (2.9 l)
BLACKHAWK      w/o lube monitor 1.75 qts (1.66 l)         with lube monitor 2.5 qts (2.61 l) TR                           approx 4 qts (3.80 l)
TRS                         approx 3 qts (2.90 l)
Gear Ratio:
You can tell what gear ratio your drive is by looking at the stamp on the side of the upper gearcase (see picture above).

The Gen 2 Alpha now has a revised lower gear ratio since 1996 which changes the overall gear ratio by a small amount. The upper gear ratios has not changed.

You can use the "drive gear ratio chart" to see what the letter thats stamped on the yoke (splined shaft) corresponds too. Drive Gear Ratio

You may also count the teeth of the upper gears to find out as well. Sometimes drives are regeared to a different gear ratio that is marked on the drive. So to find out what exactly you have here is a chart that will tell you the letter stamp/ratio as well as the gear tooth count for the different ratios. Drive Gear Ratio
Mercruiser Drive - Must Know Info:
1973 and earlier drives have a short shift throw and are not compatible with the 1974 and newer drives. So when replacing drives or swapping out gear cases. Keep this in mind.

The in-line number 1 drive before the R(redesigned), MR(mercruiser redesigned), and Alpha drives have a short splinded yoke 8 1/8 in (20.6cm) and the newer R, MR, and Alpha have a longer splined yoke of 9 9/16 (24.3cm). They will not interchange, as yoke and coupler damage will result.

The earlier number 1 drive and the R drive have a preload pin on top of the drive shaft on the lower gear case. This pin preloads the upper drive shaft bearing. The MR and Alpha drives have been redesigned where the gear angles have been changed as to push the pinion gear upward. So now the preload is in the opposit direction and the preload pin is no longer needed.

New replacement drive shafts in the lower gear housing have done away with the o-ring groove at the top of the shaft. This is for both drive shafts with and without the preload pin.

Mercruiser number one drive and the 1st generation alpha drive are interchangeable starting with the year of 1974. There will be a slight miss match where the drive attaches to the bell housing.
1st generation Alpha Drive and 2nd generation Alpha Drive
Difference between Gen I and Gen II Alpha Drive:
(see picture above for comparison - top is 2nd gen)

The attachment point of the hydraulic rams on the 2nd generation alpha is much wider apart than the 1st generation alpha, and the pin is held in by e-clips rather than locking nuts.

The upper and the lower gear housings are through bolted on the 2nd generation alphas where the 1st generations use studs.

The 2nd generation alphas use an all stainless water pump housing versus a plastic housing.

The gear lube circulates throught the driveshaft from lower to upper for better cooling on the 2nd generations.

The 2nd gen alpha has been structurally redesigned.

The 1st generation alphas can not be swapped out with the 2nd generation alphas and vise-versa.
Early style drive with preload pin and alpha drive with no preload pin
Picture above shows the difference in the drive shaft of an earlier number 1 drive with a preload pin and a rounded cavitation plate. The other drive is of a 1st generation alpha without the preload pin and a squared off cavitation plate. The drive with the preload pin has a short shift throw (pre 1974) as well. The only way to tell if it has a short or long shift travel is by serial number or to actually have to compare shift shaft travel between drives.
Early style in-line drive with short splined yoke and an alpha drive with a longer splinded yoke
Picture above shows the difference between an earlier in-line number 1 drive with the short splined yoke (bottom) and the Alpha drive with the longer splined yoke (top).
Blue Water Marine     8690 S. Oceana Drive,    Montague Mi.  49437
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