Repowering an 1971 18' SS Mercruiser?

[djmeaney]

I picked up my new to me 18' SS last week. It currently has a 2.5L Mercruiser with some issues.

After looking at the brochures, looks as though this model originally came with a 3.0L Mercruiser. Rather than fuss with the old motor with less HP, I figured that I would replace with a used 3.0. Also thought I would rather do it now than in the spring when there may be a few more poorly winterized motors with potentially cracked blocks on the market.

I have a couple of leads on used 3.0 motors -- one is from a mid-80's glasser. The seller is willing to run the motor for me and do a compression test. The asking price is about $500. Does that seem about right? (located in New England if that helps).

Also, for those that have replaced inboards -- I presume that it was necessary to remove the rear deck to get the hoist on the engine's rear lifting point. Is that right.

Thanks for the help. I hope to post some pics of the boat soon....

Dan

 

[dozerII]

Re: Repowering an 1971 18' SS Mercruiser?

Hey Dan, That doesen't sound like a bad deal. You will prolly have to use the out drive off the newer one as well, the newer one will be Alpha 1 and the one on the boat will be pre Alpha. The guys in the Mercruiser section will be able to tell you for sure. The motor will come out without taking off the rear deck, just the dog house and seating next to it. Hope it works out for you.

 

[starcrafter65]

Re: Repowering an 1971 18' SS Mercruiser?

I replaced the 2.5 on mine with a 3.0 and Alpha 1 = works great - you don't have to remove the back deck = click on my link - $500 is good - hear the engine run and check the compression - should be 120+ and EVEN across all cylinders

 

[CheapboatKev]

Re: Repowering an 1971 18' SS Mercruiser?

Welcome aboard..I agree to make sure you use the current OD that the donor motor will have s make sure you pull the drain plug and hold a magnent under the first few seconds of what comes out and look for steel shavings.
It is a pretty straightforward procedure to swap motors..But I have to ask..
What is going on with the current motor? Can it be repaired for less than 500 and all the work?
You will go from a 120hp to a 140 I assume, and honestly there isnt a huge performance difference with 20 hp.
a 120 to a 165 I6..now that would be noticeable.

 

[djmeaney]

Re: Repowering an 1971 18' SS Mercruiser?

Welcome aboard..I agree to make sure you use the current OD that the donor motor will have s make sure you pull the drain plug and hold a magnent under the first few seconds of what comes out and look for steel shavings.
It is a pretty straightforward procedure to swap motors..But I have to ask..
What is going on with the current motor? Can it be repaired for less than 500 and all the work?
You will go from a 120hp to a 140 I assume, and honestly there isnt a huge performance difference with 20 hp.
a 120 to a 165 I6..now that would be noticeable.

CheapboatKev,

I pulled the dipstick when I looked at the boat and the oil was the color of a vanilla milkshake! I've torn into the engine a bit and it looks like the head is cracked -- see pic below. Also. when taking off the manifold there was a spot on the block that had been welded about 2 to 3 inches. So between a currently cracked head and a previously cracked block it seems like a good time to repower and part out the old motor to recoup some of my investment.

If a 2.5 came along at the right price I would consider, but used 3.0 seem more plentiful.

 

[djmeaney]

Re: Repowering an 1971 18' SS Mercruiser?

Starcrafter65 thanks for the link to your restoration. Looks great. I have much more modest plans for my Starcraft. First, I'll repower and have some fun with her. When the deck gets bad I'll think about gutting and rebuilding as other on the forum have done.