Mercruiser 470 Replacement

Mattb22006

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Can anyone provide me with some optimal replacement options for a 1987 470 Mercruiser engine? I picked up a used boat for very cheap with the intention of replacing this motor. I've heard alot of bad stories about the 470 and dont want to deal with it. My intention is to buy a used motor. Not new or re-manufactured. Also if anyone could point me to some threads of people who have undergone this process that would be killer :)
 

Scott Danforth

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first, the 470 can be a viable motor, especially if its running and been maintained. it just takes more work than others to keep going

a 4.3 would be my first choice, and then you can keep the drive you have.

however if your motor is dead, i would replace the motor and drive with a 1996 or later V6 or V8 and alpha drive. you get the vortec heads and the Alpha 1, Gen 2 drive.
 

stonyloam

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Yeah, knowing how much Scott loves 470?s (LOL), that is good advice. It is WAY easier to fix a few common 470 issues than fooling around with an engine swap. If you gotta do it, there is only one choice, a 4.3 V6 IMHO. A 3.0 lacks the power, a V8 is heavy and both would need an outdrive gear ratio change. The 4.3 uses the same gear ratio as the 470. If you get a used engine, make sure you hear it run or you may not be any better off than with the 470.
 

Bondo

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Ayuh,.... You'll need a Complete 4.3l, 'n it's y-pipe to hook up the exhaust to do the swap,....
 

Scott Danforth

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Yeah, knowing how much Scott loves 470?s (LOL), that is good advice.

the design is what happens when the design is partially done and the engineer goes out and does peyote for lunch..... as I have stated prior, a few mods and it could be a great motor
 

Mattb22006

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Thanks guys! Other than a few glance overs I havent actually torn down this motor or tested it yet so it could be repairable. Previous owner stopped using it in 2016 because it was mixing coolant and oil. But thanks for the suggestions. I'll look into the 4.3 if this motor is a no-go.
 

stonyloam

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If it is mixing coolant with oil chances are that the cam seals are shot, and the weep hole on the engine waterpump is plugged. Find the little hole on the lower starboard side of the pump housing, probe with a wire to make sure it is open. If you can get it started, see if coolant is leaking out. The other problem could be the head gasket, do a compression check if you can get it to turn over. You can replace the seals for less than $100, the head gasket maybe $175. Both are DIY jobs.
 

Mattb22006

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Thats my plan bud. So you do recommend I try firing it up? I'm gonna do a compression test and clear the weep hole, and change the oil beforehand.
 

Scott Danforth

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pressure test the cooling system to determine why it was mixing coolant and oil, the usual culprits are the cam bearings, or the head gasekt. speedy sleeve the cam snout and replace the seals, use an OEM Mercruiser head gasket

if its the water pump, replace the water pump, and inspect the cam snout

change oil and filter prior to attempting to crank.

depending on how long the motor sat, you may have to clean the fuel system. since it was 2016, you may get lucky, then again, you may have to clean everything from the tank to the carb

head gaskets go if you do not keep up on the impeller and replace it every 2 years. the design of aluminum block with floating bores and an iron head does not tolerate any overheat.
 

Mattb22006

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One more question. Any recommendations on cleaning out the motor since it is full mixed coolant/oil. Just several oil changes?
 

Benny67

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One more question. Any recommendations on cleaning out the motor since it is full mixed coolant/oil. Just several oil changes?

I'd change it, run it with some sea foam in the new oil and see what the dipstick looks like after a few min. .

If it's leaked into the motor from the seal, chances are there's not a lot in there...

Also,

Don't believe everything you read, the 470 is a gas sipping powerhouse and when treated correctly is a reliable powerplant. You just need to be a bit more attentive to it and NEVER ...EVER let it overheat.
 

stonyloam

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the design is what happens when the design is partially done and the engineer goes out and does peyote for lunch..... as I have stated prior, a few mods and it could be a great motor

Yeah, with a cast iron block, they might still be making them, would have been heavier, but a pretty solid engine, especially with closed cooling. You are right, the engineers designed an engine that needed a strict schedule of routine maintanence, which if you are a DIY owner is OK, but pretty expensive if you are not. As a result impellers were neglected and weep holes plugged and $400 for a voltage regulator lead to a lot of engine failures and a (deserved) bad reputation. The one thing that the engineers did not factor in was the boat owners LOL!
 

Mattb22006

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The good news here boys is that someone already did the alternator conversion and the 4" heat exchanger upgrade for me before I bought it :) $600 for a boat and a trailer aint to shabby after all!
 

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stonyloam

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If you need to winterize it, there are two plugs on the underside of the aft end of the exchanger (7/16 I think), just pull the AFTMOST plug to drain the raw water from the exchanger. Check the coolant in the block with an antifreeze tester to make sure it has enough antifreeze in it. Not bad for $600👍
 
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