OMC Gearcase Questions

Twainer

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May 10, 2016
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Boat title says it is a 1978 Mark Twain. On the gearcase it just says OMC Sterndrive (no 400 or 800) with a 235hp on a sticker below that. According to the Clymer's Shop Manual that I have, the 235hp set up was for 1977 models. Tag on the gearcase says Model# 983489 - Serial# J351978. So does this make it a Electromatic gearcase? The change happened between 77 & 78 so I want to make sure. If so can I use Lucas 80-90W high performance gear oil?
 

southkogs

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I think '77 was the last year for the 235HP. But the model number would be on the engine tag - typically on the starboard side somewhere around the rear motor mount. The number should read something similar to 990240E 1977.

Yes, yours would be an electric shift. Lower gear case needs to be Type C lube. Upper gear case can be any that you like. The lower needs a thinner lube otherwise the shifting doesn't work quite right.
 

Scott Danforth

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throw the clymer manual away (they are filled with incorrect information and are best used as knee pads) get a factory manual

most boat manufacturers used motor/drive combinations until they ran out of stock. this may be 2 or 3 years after OMG stopped producing
 

Twainer

Petty Officer 2nd Class
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May 10, 2016
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163
I think '77 was the last year for the 235HP. But the model number would be on the engine tag - typically on the starboard side somewhere around the rear motor mount. The number should read something similar to 990240E 1977.

Yes, yours would be an electric shift. Lower gear case needs to be Type C lube. Upper gear case can be any that you like. The lower needs a thinner lube otherwise the shifting doesn't work quite right.

990241G is what I have pulled from something.
 

Twainer

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May 10, 2016
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throw the clymer manual away (they are filled with incorrect information and are best used as knee pads) get a factory manual

most boat manufacturers used motor/drive combinations until they ran out of stock. this may be 2 or 3 years after OMG stopped producing

Where does one find a factory manual for this old girl?
 

Scott Danforth

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Twainer

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