Different size engines require different gear ratios in the drive. The manufacturer changes these ratios with different
gear sets. The gear ratio change is in the upper gear housing*. All 1973 - 1985 OMC upper gear housings are
identical** except for the tooth count on the gears and left or right steering worm gear. Below is a chart
showing the tooth count for the different size engines used with OMC sterndrives.
*All lower gear housing ratios are either 2.0:1 for the four-cylinder engines or 1.83:1 for the six,,
and eight-cylinder engines.
**The original driven gears in 1973 - 1974 upper gear housings are not machined for a centering
cone. All 1975 and newer driven gears and all GLM replacement driven gears are machine for a centering cone. A new
drive shaft with shorter splines and a centering cone must be installed when replacing the original (non-centering cone) driven
gear.
| 400 / 800 / Stringer Upper Unit |
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| OMC 800 upper gearcase rebuilt |
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Rebuilt unit includes:
New Parts:
- Gears (Drive / Driven)
- 4 Bearings
- Oil seals, o-rings and gaskets
- Water pump assembly (impeller housing and impeller)
- Ball gears
Machined parts:
- Water pump shaft*
- Drive shaft*
*If drive shaft groves requires machining of more than .010 of an inch or water pump shaft splines male or female
are more than 20% worn, new shafts will be installed into the upper gearcase housing
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