Merc. Lower Unit #s....?

[MattinTally]

I have a 3-Cyl 1988 90hp Merc ELPTO motor with a blown foot. Serial on my engine is B347250. Took foot off and looked at the casting number on inside of lower unit on top of the cavitation plate. The number is 1667-9010-C with a smaller numeral 5 after the "C". I have found someone with a 1987 80hp 3-Cyl, but the part number on his lower unit housing is slightly different.... 1667-9010-C1, not C5. Serial on his engine is B218952. Does anyone know for sure if these are compatible?

I measured my drive shaft and its 20". He states his is 22.5". I thought they were either 20" or 25"...... not in-between. But, the amatuer I am, I could be measuring improperly. I measured from the base of the drive shaft, where it enters the water pump housing cover, up to the splines.

Any advice would be greatly appreciated.

 

[emckelvy]

Re: Merc. Lower Unit #s....?

The 80hp L/U is interchangeable with your 90hp. Those motors are virtually identical except for differences in the powerhead which account for the HP difference.

BTW shaft length (i.e. Longshaft Shortshaft etc) is not determined by the actual measurement on the driveshaft.

It's determined by measuring the distance between where the motor sits on the transom, to the anti-ventilation plate (also mistakenly called the cavitation plate) on the lower unit. This would be 20" for a Longshaft, 15" for a Short, 25" for an Xtra Long.

If you want to directly compare driveshaft lengths, the most accurate way to do that would be to measure from the L/U's mounting flange (the flat surface of the gearcase where it fits up to the center section), to the very top of the driveshaft. This number won't correspond to the 20" measurement but both units should be the same measurement, providing the method of measuring is the same.

HTH........edc

 

[trihullskiff]

Re: Merc. Lower Unit #s....?

It is also important to verify the number of splines on the drive shaft as there are variations.