76' lower unit does not fit 69' ? (pictures)

Motor is a Merc 1000 (100hp) I'm not 100% sure what year it is but the serial i got off the plate is 2409569. The lower unit gave out. First it did not go into rev and now it wouldn't even hit neutral. I picked up a used lower unit that came off a 1976 115hp motor. Upon installation I noticed that the 76' lower unit has small guides and my old LU does not. I've been reading that most LU of the same time frame would be compatible.

Here are a couple pictures of the supposed 76' lower unit. Please let me know if you need a view of a certain spot to help identify.





I'm trying my best to get the boat ready for water on labor day so any and all help would be very appreciated.

Re: 76' lower unit does not fit 69' ? (pictures)

If you mean the mounting studs ,measure the drive shaft as someone may have add a long shaft kit to it.

Re: 76' lower unit does not fit 69' ? (pictures)

Faztbullet said:

If you mean the mounting studs ,measure the drive shaft as someone may have add a long shaft kit to it.

Click to expand...

I circled what I am referring to in red. My old LU did not have these. I checked the underside the midsection and it definitely does not have a hole for the mounting guides.

Re: 76' lower unit does not fit 69' ? (pictures)

I think you're referring to the little stainless dowel pins pressed into the gearcase, fore and aft. These are supposed to help locate the lower unit to the midsection so it maintains 'perfect' alignment and doesn't 'walk' around.

You're correct that the older motors don't have those dowel pins. Just grab hold of them with a good set of Vise Grips and pull them out. It'll work just fine.

The one question I have, looking at your pics of the water pump, something else besides the plastic guide tube is sticking out of there. Hopefully it's not the copper water tube that's supposed to stay up in the center section (exhaust tower). No way you're gonna get the water tube engaged at the upper end if it's stuck in the pump.

I'm just hoping it's some sort of extra rubber sleeve or something, can't see enough of it to be sure.

HTH & Have a good Labor Day..........ed

Re: 76' lower unit does not fit 69' ? (pictures)

Take a pair of vise-grips or stout pair of sidecutters and twist/pull them out as they are pressed in. If you cant budge em apply a little heat or grind then flush with dremel tool. Also make sure water tube(copper) is in midsection as it looks to have come out with unit.

Re: 76' lower unit does not fit 69' ? (pictures)

dowel pin are the words I'm looking for. Thanks! I didn't want to do anything before I was sure of what to do. And the thing you see above the water pump is pretty much what you think. Just a sleeve I put to help with guiding when reinstalling the LU.

Now another thing is bothering me. I just measured each LU. They are NOT the same size. All the mounting holes and studs line up. It's a bit hard to tell in the pictures but my old LU measures a bit over 19" and the newer LU measures just a tad longer then 20"

old LU:

newer LU:

Re: 76' lower unit does not fit 69' ? (pictures)

Just a slight redesign of the gearcase. There might be a 'hair' hanging out at one end or another, but operationally it'll make no difference since all the mounting points are identical.

Everything will fit up just fine once you remove those dowel pins.............ed

Re: 76' lower unit does not fit 69' ? (pictures)

thank you Ed..... and everyone else for the very helpful replies. I am very intent on getting this boat on the water this coming weekend so i appreciate all your help.

Since I have the LU off, I'd like to change out the copper water pipe. Just for good measure i guess. Not to mention It looks easy. Where can I get the copper pipe and what size/length do I look for? Is this something I can go to home depot for?

Re: 76' lower unit does not fit 69' ? (pictures)

Unless it's completely and hopelessly mangled, I'd leave it alone. You don't realize what a potential can of Worms replacing that water tube can be.

Depending on how things are in the upper end, you might pull it out but won't be able to get it back in without pulling the powerhead. All it takes is for that upper rubber grommet to roll over a bit, in the way of the tube, and it's All She Wrote. That could put a slight crimp in the Labor Day Weekend plans!!

Seriously, I'd wire-brush the end where it goes into the pump, so it's nice and clean. If it's squished out-of-round, bend it back into shape. Copper is quite malleable and you'd be surprised what you can do with it. If it's real bad, open up the end by sticking a closed pair of needle-nosed pliers in there. Roll them around a bit and you can easily 'reform' the tube. Once you're close, find a metal rod or suitable-sized bolt to fit in the I.D. of the tube, then tap the outside with a small hammer, just like using a body dolly.

De-burr any rough edges so it'll slip smoothly into the pump grommet. Smear a dab of waterproof boat bearing grease on the tube to help. Grease up all your bolts & the studs; it'll keep them from seizing up and make disassembly so much easier next time. Be sure to grease the driveshaft splines too, but wipe any excess off the top of the driveshaft.

Here's a link to an exploded view of the exhaust plate, which retains the water tube upper grommet, so you'll be able to see what you're up against:

http://www.mercruiserparts.com/Show...8&bnbr=14&bdesc=BOTTOM+COWL+AND+SHIFT+LINKAGE

Cheers.........ed

Re: 76' lower unit does not fit 69' ? (pictures)

speaking of the drive shaft spline, is it necessary to cut the grove for the O-ring? The older drive shaft has one but the newer one does not. Can i get by without the O-ring or is it completely necessary?

Re: 76' lower unit does not fit 69' ? (pictures)

The O-ring keeps water out of the crankshaft splines. If you're running in salt water, you really need that O-ring in there or the crank and driveshaft are gonna rust together.

If you're in fresh water exclusively, you might get by without, but I'd pull the lower unit at least once a year to lube the driveshaft splines.

All you really need is a thin cutoff wheel, I took one meant for a "nukie" (pneumatic) grinder and used an arbor setup to chuck in my 3/8" electric drill. It didn't take too long to make a proper groove.

For the correct location of the groove, measure the distance from a reference point on the 100HP gearcase (such as the mounting flange) to the O-ring, and transfer to the 115 driveshaft.

HTH........ed

Re: 76' lower unit does not fit 69' ? (pictures)

hmm.. i will be using the motor in both fresh and salt so I'll take the time to cut in the grove. I have a good dremel that will hopefully do the job.