You know what they say about curiousity. I don't mind telling boat stories if you don't mind listening.
This yard sale boat is an older boat. Pretty much a classic these days from back when boats purpose built for bass fishing were first being seen. What attracted me to it was that it was in nearly mint condition. Obviously garage kept since new, because it still has its original, 30 year old interior with no sun or water damage and not a stitch out of place. What's more, these old bass boats were more utilitarian in some ways than the modern 70 mph run and gun rigs. Lots of storage compartments, two of which can work as either wet wells or dry storage...or built in coolers if you prefer. It has a very large aerated live well. A concealed rod locker. Also had a newer trolling motor, a fairly up to date sonar unit, and a nice radio installed. It was powered by a 65 hp Mercury. I knew I was taking a chance on the motor, because the near-80 yo guy selling it said he hadn't really used the boat at all in the past few years.
It started right up when I got it home, albeit with a little stumble at idle that I attributed to old gas and dirty carbs. Given how well it started though, I decided to pour some Seafoam in the tank and try it out at a lake that very day. Well, it overheated badly on the water.

I took it home and pulled the exhaust cover and noted that pistons 1 and 2 were melted and their respective cylinders scored badly. I dropped the lower unit and noted the water pump was completely shot. I concluded the motor was fucked. And damnit, I
know that an old water pump impellor that has sat dry a few years is bad news. I generally have the one on my Nissan changed yearly as cheap insurance. Anyway, I couldn't really say the old guy had screwed me over. Hell...it's an old boat and buyer beware is an old story. Besides, I think it was really me who finished off the motor in my eagerness to try it out on the water. But no matter...I obviously needed a different motor or a rebuild on the toasted 65 hp.
Well a rebuild of the 65 might make sense for some of those guys who just absolutely have to have a period correct motor to hang on their vintage boat, but I could find late model, low hour motors for not a great deal more than it would cost. Made no sense to my utilitarian mind.
My son happened to know a guy who fishes bass and catfish tournaments though, and he happened to have a 40 hp Mercury that he had taken off his catfish boat. It would be a cut in power and in fact the guy had taken it off his boat to repower to 120 hp....but he said it had pushed his catfish boat about 25 mph. Not really fast enough for tournament fishing I guess, but it was priced reasonable and the guy said he would stand behind it to the point that if I just wasn't satisfied he would give me my money back. What was best about the deal though, was that in looking at it, it seemed that Mercury had made very few changes between their mid size motors from year to year and even model to model. The 65 hp and 40 hp motors were very alike with the exception that the 65 had an extra cylinder and an extra carb. A motor swap looked to be a straight forward proposition.
My idea was to take the 65 off my boat while leaving its mounting brackets in place since my motor had power trim/ tilt and the replacement didn't. I definately wanted to retain that feature, and it seemed like the easiest thing would be to just remove the motor from its pivot point or whatever the hell they call it.
So I took the boat to work and put it in our shop, figuring the overhead crane would be the thing to use in removing the motor. I unhooked lots of stuff and kept finding more stuff that needed unhooked or removed in order to remove that pivot post. Now it doesn't take long to tell, but there were several hours of unhooking, removing, head scratching, standing back and pondering....
I finally came to the unavoidable conclusion that the outboard engineers at Mercury Marine had fiendishly designed their product so that pivot post couldn't be removed without virtually disassembling the motor. At least the power head had to come off the top of the motor. And that's obviously easier to do if the lower unit is first removed. Oh well...I was going to have to take that off the replacement motor to put a new water pump impellor in it anyway. I learned my lesson on that score.
I did the disassembly on the 65 first since it was already scrap. I fabricated a stand to hold the 40 while it waited its turn. Surprisingly, the powerhead wasn't that difficult to take off though it was heavy as a bitch and the overhead crane came in handy. So all that was left on the boat was the middle exhaust leg of the motor. Then I had a brainstorm. The middle exhaust legs of the 65 and 40 looked identical. Why not just put the 40's powerhead and lower unit on the 65's exhaust leg and forget about that damnable pivot thingamajig? (It being attached to the middle exhaust leg.)
Well everything looked identical enough...but it wasn't because the 40 hp powerhead wouldn't bolt down all the way to the exhaust leg. Further examination proved that the lower cowling of the powerhead was very slightly different. Okay...I was still wanting to avoid fucking with that pivot thing if I didn't have to, so I figured I would just unbolt the four mounting shocks from the exhaust leg and install it that way. I wasn't out anything since the powerhead had to be removed to get to two of those also, their nuts being cleverly hidden inside the exhaust leg instead of stupidly the other way 'round where any fool could get to them. Wrong answer again. While unbolting them I noticed I had to use a different wrench on the 40. Its mounting shocks were slightly smaller and the holes they went through in the exhaust leg were also smaller. They would be a way sloppy fit on the bracket on the boat I needed to bolt them to and that's part of the power trim that I wanted to retain and which is the whole point of this
clusterfuck exercise.
So I finally compared the exhaust legs very closely and I see that the cowling is only interfering because on the 65 leg the front corners are squared off and on the 40 they're slightly rounded. It was done only for the cosmetic reason of the newer, more modern looking cowling on the 40. What the hell....I only have to take an angle grinder and remove about a 16th of an inch of aluminum to radius those corners so it will fit, and I do, and damn if it don't.
The power head being on, I made mental note to not forget to put a little plastic thing called a shifter rod guide back in the lower unit when I put it on and went about putting in the new water pump impellor. After that was done, I bolted the lower unit on and lo and behold I had a complete motor back on the boat. Which wouldn't shift because I forgot to put the shifter rod guide back in. That was enough for that night.
The next day I rectified the shifter rod guide error and then set about hooking up all the peripherals. The shifter linkage and throttle linkage were pretty straightforward though finicky as fuck for my fumbly fingers to fiddle with. I noticed I had to adjust the hell out of the throttle linkage to get it in right. The electrical connection on the 65 was a square plug and it was round on the 40 so that couldn't be just simply plugged in. The wiring was the same though and the 6 or 7 wires were even color coded identically so I just switched the plug ends.
At last it was time to fire the new motor. It fired right up. And immediately screamed to full throttle because I had installed the throttle linkage so that the throttle handle was at idle while the carb was wide open. I turned the key but the motor didn't die because some dumbass who switched the electrical plugs hadn't securely crimped the orange wire....and that was the one that kills the motor. Some dumbass kept his wits enough to stab the choke button though and kill the motor that way. Then that dumbass took another hour or so to do some more finicky fumble fucking with the throttle linkage to put it back the way it was in the first place.
That all sorted out, I started it again and it leaked water all over the place. Oh shit...I first figured the powerhead gasket was leaking even though it was a new one I had just installed. But looking closer, I found a little water hose that was split. Of course you can't get to one end of it without taking half the motor apart. However that end is in good shape so I cut off the bad end intending to just splice in a new piece. That's when I found out why the hose was split. It goes on a bigger fitting at one end than at the other. Some special part that someone replaced with a regular hose by splitting the one end enough to get it on the bigger fitting. It worked for a long time I guess but eventually the split widened and started leaking. I went to the hardware store and got some fittings to fabricate connecting a larger hose to the smaller one and that worked fine though it was
awful fumblefucky to get in place.
Well it's on the boat and ready to go now. I've been over it plenty checking and re-checking. It idles great, pumps water beautifully, and doesn't run hot. All that's left is the maiden voyage, scheduled for tomorrow or the next day.
Ain't you glad you asked?