[basscats]

mine is a 1987 115 inline six mariner lower unit
will a 1989 150 lower unit fit my motor

[emckelvy]

No. A lower unit from a V6 definitely will not fit your Inline Six. Nor will a lower unit from any of the various Big Bore 3 and 4-cyl motors (circa '89 and up, with fiberglass 'clamshell' type engine covers).

You need a lower unit from another Inline six, vintage '79 or newer. Or from a 75-80 HP 66 C.I. Inline Four (older style with a wraparound cowling).

The '79-and-up 6-cyl L/U is an exact replacement for yours; the 4-cyl models have a different gear ratio (2.3:1 vice 2:1), and the only thing that will affect is the prop pitch if the Six rev's up too much with that gearbox. Simple matter of repropping with 2" more pitch.

Note, older Six and Four L/U's from '66 up may fit, but are not of the "improved" gearcase style. And if looking at an older L/U, shaft corrosion is a big issue due to carbon steel driveshafts (yours has stainless).

HTH..................ed

[basscats]

thanks for the answer
my first post
basscats

[Chris1956]

Ed, I am surprized that it won't fit. I was advised that my '77 Merc 1500 inline lower unit would fit my '93 135V6, with some simple modifications. it would seem logical that the reverse was true as well. Is his '87 Lu different from the '77 inline six LU?

[emckelvy]

While the shift shaft location, front 2 studs position, water pump and driveshaft look eerily similar between the Inline and V6 gearcases, there are significant differences aft of there.

The V6 gearcase is quite a bit longer. Don't know if the spacing of the (2) studs underneath is the same, maybe someone with a V6 gearcase could do a bit of measuring. The exhaust tube area on the V6 is way bigger.

Here's another thought about swapping; the Inline gearcase likely wouldn't last long being torqued by a Mighty V6. Conversely, the V6 gearcase takes larger dia props and we all know Inlines don't like to swing those, eh!

I've posted a few poor quality eBay pics to illustrate the differences.

HTH............ed