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  1. J

    Replacing thermostat on (very) old Mercruiser 120

    There is a bit of a counterbore (somewhat rusted, though). I've decided not to perform electrolysis on the manifold because I've read that will just give fresh clean metal and may actually accelerate future rusting. I did have someone recommend using a bit of Permatex aircraft sealant to help...
  2. J

    Replacing thermostat on (very) old Mercruiser 120

    To be clear, this is a 35891 manifold and a 35892 exhaust elbow, 1963-66. It's officially used for a 110, but apparently was also fitted to 120's and possibly others. I've attached a good picture of this model manifold and elbow. I know exactly where the thermostat goes on this (nearly 60 year...
  3. J

    Replacing thermostat on (very) old Mercruiser 120

    Then I must have the wrong thermostat, as nothing holds it in place. Once the elbow is tightened down, I suppose friction would hold it, but I can't see how, with the manifold installed on the engine, one would keep the thermostat from falling down by gravity before the elbow can be installed...
  4. J

    Replacing thermostat on (very) old Mercruiser 120

    Actually, it's out of the boat right now, so I can (and probably will) just find a way to hold it upright. But in the future, it would be nice to be able to replace it without pulling the manifold (though not a huge deal). Here's a video of the thermostat, which is just loose in the hole...
  5. J

    Replacing thermostat on (very) old Mercruiser 120

    My manifold is this very old style (see attached image). It appears that my (only) thermostat is (regrettably) located at the back of the manifold. 3 questions: 1. A simple logistical question: Aside from taking the entire manifold off and building a stand for it to hold it in a position such...
  6. J

    Engine Alignment, weird issue

    Older starcraft boat with a 120hp Mercruiser, and a pre-alpha outdrive. I removed the engine to replace the coupler which was trashed by shifting into gear at a very high RPM (another post/another story). The engine is re-installed, and the hardware on the rear mounts is the double-wound springs...
  7. J

    What all did I just break???

    73 Starcraft with a 120hp 4cyl, and a pre-alpha sterndrive. I was in the water ready to ski, and my daughter had trouble starting it. I said give it a little gas when you start it. Well, she proceeded to start it and immediately PUT IT INTO GEAR while it was still at a rather high rpm...
  8. J

    ISO a device to kill engine in overtemp or under (oil)pressure conditions

    Having completed spending lots of money on a rebuild bill, and now getting a 2.5L 120 Mercruiser re-installed after a quick overheat caused by a bit of sand in the outdrive, it occurs to me that... it's 2015, so why can't I find a simple device to shut down an (old, 1972) engine when the...
  9. J

    Correct tool to access 1/2" exhaust elbow bolts on 120

    I have an old (1969) 120hp, recently overhauled, which overheated. The impeller is fairly new, and is pumping steadily into the boat, so I wish to check the thermostat between the manifold and exhaust elbow. I fear it may be stuck or missing (if missing, the water may not be cooling the...
  10. J

    Mercruiser old style engine mounting question

    I removed and am about to re-install (after engine work) my 120hp 2.5L engine. The serial number is 183.... (early style). The Merc Manual #1 specifies that the rear mount, given this serial number, should use half of the double-wound spring (it specifies the spring should be cut to make it a...
  11. J

    Standard Exhaust Shutter (Flapper) Won't Fit + ISO 140 Motor

    I've got a pre-alpha, and trying to fit an exhaust shutter (sierra 18-2727), which is meant to fit 120/140 exhausts. Trouble is, it doesn't. The hinge pin on the sierra is too long, in fact. The 18-2727 (60930 Mercruiser #) is what keeps coming up on various parts sites, and even when calling...
  12. J

    Where is 0 on Mercruiser 120 timing tab (image included)?

    My timing tab (shown below) is very worn, and I'm missing two key pieces of information: #1. Where is 0 at on the tab? #2. What the the increments of the lines on the tab (I assume 2 degrees each)? It's a 1969 Mercruiser 120 Does anyone have this info?
  13. J

    Replace Head Gasket or Replace Engine

    Let me preface this post by explaining I'm not particularly mechanically inclined, and make no claims that I am. I'll be the first to admit by ignorance about boat drivetrains. The problem is on a Mercruiser 120 4-cyl in a 1973 Starcraft. Ran just fine until, quite suddenly, a loss of power...
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