How "interchangeable" is a Mecruiser?

I recently aquired a 20' 1973 Slickcraft Cuddy. The hull is in great shape and everthing is solid. I saw the boat once before I got it (cheap) and was not able to get serial #'s. It currently at a buddys shop.

From what I can tell it's an original Mercruiser inline 6 165 that is seized ~a fat guy with a socket and breaker bar on the crank couldn't budge it. The air cleaner was left off and a storm some odd while back blew the dog house off the deck. Water in turn got into the intake. The outdrive is original but had papers for the rebuild not too long ago.

My questions:
(1) would a same era style GM Merc like a 4.3, 305, or a 350 be able to "bolt up" to the outdrive? I know you can do this with car/truck motors.
(2) would it be way to much (work if even possible) or just pay to just rebuild the motor as is

I've been building hot rod motors, cramming big blocks into small cars and trucks so I am no stranger to a mechanical challenge. Then again I don't have to worry about a car sinking at the 1/8mile. I'm just wondering what might be involved in changing it out. The previous owner did state that the motor (when running) had the grunt to gettup and go, but then again he said it ran fine and shouldn't take much.

Re: How "interchangeable" is a Mecruiser?

Welcome aboard Tharsheblows..

Do yourself a favor and read the ADULTS ONLY sticky...

The motor you have is a straight 6?
How have you ascertained that the motor is frozen?

Re: How "interchangeable" is a Mecruiser?

another L6 will just bolt on up and you'll be hip. or maybe fix the one ya got.
i've never read anything bad about a L6 in particular. i'm on my second one. nice and torquie. mine have been in a 16' trihull and now the aristocraft below. both worked and work great.

while i don't know the exact facts about changing to a different engine package. i'm sure you'll have to mod your boat for ft. motor mounts on a v6 or v8. if you change engines, you need to be sure the drive ratio is correct for the new engine too. your 165hp has is 1:65/1.
at the very least the exhaust system is set up for a L6. the v engines will require a much different set up.
i'm sure others will tell you more facts than i can.
you already need an engine. that's already a lot of bread.
if you switch to a different set up. you'll spend a lot more bread that replacing what you have. + you'll be working on your boat for a while. do you want to work on your boat, or go use your boat?

another fella here has a boat like your's. think it's a 70 slickcraft though. he loves his and take his into the ocean. his is powered by a L6 too.

only drawback that i can see myself, is it's not modifiable. there are basically no upgrades to make your L6 165hp anything other than it is. which is ok with me, there are many other things on boats that you can work on other than the engine. just keep it tuned up good and it'll likely treat you very, very well....
guess you can tell, i'm for keeping it as is...

go to the adults only sticky at the top of the i/o page and get your service manual. i think you need #1. confirm by serial number. same book for the drive, confirm by s/n. the facts on you set up are in these books. also, the facts on some of the other set ups your considering too.

Re: How "interchangeable" is a Mecruiser?

CheapboatKev said:

Welcome aboard Tharsheblows..

Do yourself a favor and read the ADULTS ONLY sticky...

The motor you have is a straight 6?
How have you ascertained that the motor is frozen?

Click to expand...

Certain it's frozen. And yes it's a staight 6. I know with GM mostly everything is interchangeable. My concern is the new "heart" being able to bolt up to the outdrive. I just don't want to get into a $$$$$$etc project. I actually have plenty of GM blocks laying around and rebuilds are cheap and easy. Outdrives aren't from what I can see.

Re: How "interchangeable" is a Mecruiser?

I actually have plenty of GM blocks laying around and rebuilds are cheap and easy.

Click to expand...

Will you be my neighbor?

Re: How "interchangeable" is a Mecruiser?

You'll have issues going from the "in line" six to a "V" engine.

1. The drive gear ratio wrong for a "V" engine.

2. The engine mounts are different.

3. You'll need a "Y pipe" at minimum, for the exhaust.

4. Your GM block may not be marine ready.

5. You will need ALL the hang on stuff, from a V" block; manifolds, alternator, carburetor, starter, coupler?,

It's not as simple as a car/truck.

The in line 165 is easy and relatively inexpensive to rebuild.

Re: How "interchangeable" is a Mecruiser?

4. Your GM block may not be marine ready.
Hi DJ when you say not marine ready what do you mean exactly with the block? was just curious. thanks.

Re: How "interchangeable" is a Mecruiser?

Sure. My neighbors hate me.

Re: How "interchangeable" is a Mecruiser?

Welcome aboard !

Want to listen to a old geezer and pull off the drive and try turning the motor again.

Might be the drive frozen and not the motor.

Take the plugs out shoot the holes with pb blaster and try turning it, shoot it again rock it back and forth.

Or pull the motor out cause thats what i would do and turn it over pull off the pan and see whats what.

You know the drill.

Good luck and keep us posted.

Re: How "interchangeable" is a Mecruiser?

Tharsheblows said:

Certain it's frozen. And yes it's a staight 6. I know with GM mostly everything is interchangeable. My concern is the new "heart" being able to bolt up to the outdrive. I just don't want to get into a $$$$$$etc project. I actually have plenty of GM blocks laying around and rebuilds are cheap and easy. Outdrives aren't from what I can see.

Click to expand...

Like Chief mentions, pull the outdrive and then make sure the engine is seized. (It probably is the engine... but just because a "big boy with a big breaker bar" can't turn the engine over doesn't mean the problem lies in the engine. By removing the outdrive you are eliminating that as a possible source of the problem).

The good news? You have an easy motor to rebuild and work on. And if you do the work yourself, the parts are readily available and don't cost an arm and a leg. I recently did the same. Here's the results: http://forums.iboats.com/showthread.php?t=230711&highlight=rebuild

Good news #2? The outdrive is not terribly expensive either. You can buy a complete brand new aftermarket outdrive for around $1,200. It could well be that yours is fine of course. But even with a worse case scenario of having to rebuild the engine and buy a new outdrive you wouldn't be out more than a couple thousand dollars and you would have something that should last you a long time.