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Technical GM Mercruiser

Discussion in 'The Hokey Ass Message Board' started by mickeyc, Aug 4, 2019.

  1. mickeyc
    Joined: Jul 8, 2008
    Posts: 911


    Hello folks. There is a 1987- 3.0 -140 HP Mercruiser 4 cylinder motor
    listed in my area for sale. I would like to know some particulars regarding
    the conversion for automotive use. The motor is complete with all the
    marine gear still attached. I have looked at several posts here regarding
    this issue. I find them somewhat confusing. particularly intake and exhaust
    manifolds, and such items as trans, flywheel etc. Is this a viable motor to
    consider for a vehicle such as a Model A Ford I have that needs a motor
    to replace the one that knocks LOUDLY! I am assuming the motor has been
    used in salt water as the great fishing here about mostly is. I realize the marine
    gear is of little use, but it is complete and cheap. Thanks for any input anyone
    may care to share. Mick.
  2. gimpyshotrods
    Joined: May 20, 2009
    Posts: 16,436


    Did it go in and out of the water, or did it live in the water?
    kidcampbell71 likes this.
  3. Marty Strode
    Joined: Apr 28, 2011
    Posts: 4,195

    Marty Strode

    They work out well in Model A's. IMG_1761.JPG IMG_1762.JPG
  4. gimpyshotrods
    Joined: May 20, 2009
    Posts: 16,436



    However, it needs to be thoroughly inspected for damage from salt water.
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  5. mickeyc
    Joined: Jul 8, 2008
    Posts: 911


    It was in an 18ft day fisher. The kind you launch and pull behind a vehicle.
  6. 34Phil
    Joined: Sep 12, 2016
    Posts: 191


    A previous post said French Lake Auto Parts had cast some exhaust manifolds. Exhaust seems to be same layout as 153 as SPA turbo manifolds say for both. Impco has propane intakes and adapters for 2 or 4 bbl carbs. There were 2 sizes of 3.0 intake ports so ck. Port adapters available for late to early.
  7. There are two types of marine cooling, fresh water cooling, and direct cooling.
    With the direct cooling, if the boat is run in salt water, then salt water is picked up and run through the engine for cooling. If the boat was trailered and rinsed after use, even these salt water cooled engines will be good.
    If the boat lived in the salt chuck, then there can be problems with metal erosion in the cooling passages. I had a salt water cooled engine that failed after 8 years, but the boat lived in the water. All I had to do in this case, was replace the head and flush the motor. It lasted until I sold the boat. I might add, that when the motor failed, water got into a cylinder and it locked the engine up, causing bent push rods but no other damage.
    The fresh water cooled engine can be considered the same as an engine pulled from a car. The coolant that was passing through the engine would have normally been antifreeze.
    gimpyshotrods likes this.
  8. If the boat had a heat exchanger so salt water was not circulated through the engine it should probably be in good shape. If they circulated salt water through it I think I would pass on the engine. I assume it has low miles (or as they measure in the marine industry, low hours), why are they removing it? That is the engine I have in my AVATAR. You are right about the problem with the manifolds. Mine has been in there since the eighties and I haven’t watched what has come on to the market, you should do some research. I think any of the manifolds designed for the GM 181 industrial engine should fit but check to be sure they all us the same manifold gaskets (and thus have the same port spacing). Worst case you would need to have someone fabricate a set of custom manifolds. I used a head from a 153-passenger car on mine (and the associated manifolds) and it worked fine. The engine is the same as the GM industrial engine so you might check what is available, please post if you find anything. You should update to a street cam, the marine cam will work but the curve is not the best. The good news is that bolt pattern on the rear of the engine is the same as a small block Chevy. That means you can use a transmission adapter for an early Ford V8 transmission to a small block Chevy. They are fairly easy to find used and still available new. With the torque produced it is possible to use the stock Model A rear end. Since you are going into a Model A you will need to make pedal mounts and a wishbone mount, the ‘32 didn’t have those problems. Attached is a picture of my front engine mounts utilizing the stock motor mounts and rubber isolator, which worked out well. I also used a generator from a sixties 4 cylinder passenger car but I assume the 6 cylinder is the same.

    Charlie Stephens

    gimpyshotrods and Hnstray like this.

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