Hello, I just picked up a 1967 Larson with a 120 I/o. Avocado green.
Very cool boat. Good shape for the age. The person I got it from said it had ran two years prior. I also don't have to purchase if the motor is bad. Well I just drained the oil and got two quarts of water out of it, also the motor is seized. I am a mechanic by trade and have the equipment to rebuild, so I am not worried about that part. Not to sure what to look for on the out drive or what is needed to maintain or rebuild. I hate to stick the money in to the engine and have the drive bad. Thanks for your time.
As I recall that's about the earliest of the Mercruiser out-drives. Way before the Alpha or any of that. I have not worked on one that old. I do mostly mid-1970's - MC1 & MC2's ...
But, it's pretty straight forward. Check the oil in the lower unit. If off colored, needs seals. Park it in the sun so it gets warm and drain the lower unit. Should be minimal, metallic sheen and not much that a magnet will pick up. If you get sand size metallics, it's either eating gears or bearings ...
On something that old, you will have to go through all the "rubber" bits. Seals, hoses, bellows, etc. It would not really be safe to run with original ozone aged rubber bits.
There are some special tools needed to tear down the lower unit completely. But you may be able to borrow or rent them from a local Mecruiser shop. I don't imagine they have a ton of calls for tools for the old stuff.
If you get stuck They can help out with a particular part. Mostly they'll be parts that have corroded and won't move ... Real patience and lots of good penetrating oil will help. Easy with the heat. You do not want to warp any cases.
In any case you'll have to take it down far enough to rebuild the raw water pump and that will be far enough to get a good idea of what shape it's really in ...
You are right, you don't want to be into the motor and find out if the out-drive is bust ... You know that most of your parts will be coming off eBay ... Either NOS, or used.
If the out-drive is toast, you can find somewhat later 140 MC1 or MC2 pull-outs all over. Boats age, the interiors get ratty, the floors and stringers get rotten and they get scrapped. They usually salvage a decent out-drive and motor. They can often be had for $800 or so in decent shape ready to swap
Larsen is decent well made hull. If it's sound, a repower with a used take-out would be easy enough
Whatever you do, note that Mercruisers are hard on out-drive oil. Regular hypoid oil will not hold up well. Mercruiser has their own branded "Performance Plus" SAE 90 gear lube. It is some of the most sticky and tenacious gear oils out there. Ain't cheap, but it's all I'd ever run in an older drive. It will help it live if it's going to
Thanks for the reply. This boat was in a boat house since new. It did not come with a trailer. So I bought a trailer with a rotted out
18 foot boat with a 140. Not sure of the year or if it runs. Do these all mount up the same? I was thinking of keeping this a numbers matching boat or does it really not matter. The floor is a little soft through the center, so I am guessing that would be a good time to replace the floor. Lots of questions there also but I will post on general forum with pictures. Still need to work out the price with the owner. My wife and I have already fallen in love with this vintage boat, so hopefully we can work something out. Wasn't looking for this major of a project but o well.
I would try to save it, not too many around still in use, and it would be nice to see one preserved. The soft bits for the drive you can still get such as seals and O rings, but the gears are NLA. Bearings you can get through the bearing shops. I say have at it, and post your progress for the rest of us poor souls who love to watch this kind of stuff.