MerCruiser ALPHA ONE GEN II Upper Unit / 0L100040+ (1998+) Upper driveshaft gear housing, shafts & seals exploded diagram

Alpha One Gen II upper housing parts in this diagram

This diagram covers the upper driveshaft housing, top cover, vertical drive shaft, upper gear sets, roller bearings, shims, oil seals, U-joint components, water-guide parts, wear pads, fasteners and anode options. It does not cover the lower gear housing, propeller shaft, water pump or transom assembly.

Choose the upper gear set by ratio

Callout 7 contains alternative gear sets for different drive ratios and tooth-count combinations. Callout 8 also changes by ratio. Confirm the drive's actual ratio and match the scheduled reference. Do not select a gear set or bearing from appearance alone.

Check the 0M400411 and 0M400412 production change

Several oil-seal and U-joint components change around serial 0M400411 and 0M400412. Match the full serial number to the note on the relevant schedule row before selecting the yoke, U-joint, centre socket or related seal.

Seals, bearings and shims are selection parts

Shims set gear and bearing position, while ratio-specific gears and bearings must remain correctly paired. Individual seals are listed separately from seal kits. The diagram identifies the parts but does not replace the workshop measurements, preload settings or torque procedure required for a rebuild.

Anode choices for the Alpha One Gen II

The schedule includes separate housing and kit options in zinc, aluminium and magnesium. Select the material for the operating water and the vessel's existing corrosion-control system. Do not mix anode materials without checking the complete protection strategy.

How to use the diagram and parts schedule

1. Confirm that the equipment is MerCruiser Alpha One Gen II / OL100040+ (1998+) and check any page-level year or serial scope.
2. Find the required component on the exploded drawing and note its numbered callout.
3. Match the callout to the product code and OEM cross-reference in the parts schedule.
4. Apply every model, serial, ratio, side, material and configuration note shown for that row.
5. Compare the selected replacement with the removed part before installation.

Fitment and cross-reference checks

The page-level route is MerCruiser Alpha One Gen II / OL100040+ (1998+). It helps customers reach the correct drawing, but it does not make every product in the schedule interchangeable across every version of that model family.

An OEM number is an identification cross-reference. Confirm the exact product code, model designation and any bounded selection information before ordering. A product may also appear under another make or model only where that separate SKU-to-application fitment is independently supported.