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1990 Johnson 90 hp throttle arm question and starboard cylinder head too warm

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  • #16
    Some will argue.-----In my opinion the motor needs to come apart.


    • #17
      Is that suspicion of the lower part of the cylinder with corrosion damage, suspicion of water contamination in the lower crankcase, or my comment about the lowest part of the port side block had standing water at the bottom-most part of the cooling passageway?

      It may be a couple of weeks, possibly a month or two before I pull the powerhead. Do I need to go ahead and buy a headgasket and put it on the port side so the motor can be mothballed until I'm ready to pull the powerhead off?

      I have the head bolted on the block very loosely so as to keep moisture and other contaminates out, but not enough to torque/damage the head due to no head gasket.


      • #18
        Measure the cylinder bores. ---------Post your numbers.


        • #19
          Is the engine pumping water? Check the compression. I took the T-stats out of my 86 110 Johnson and it made no difference.


          • #20
            Originally posted by Rich672 View Post
            Is the engine pumping water? Check the compression. I took the T-stats out of my 86 110 Johnson and it made no difference.
            I have the factory service manual and know the possible spots where the issues are on cooling flow.

            It's not the water pump, pump was installed correctly and plenty of flow was coming out the tell-tale.

            It would either be the thermostats & housing issue, exhaust housing gaskets, or blockage in the cooling jackets in the block feeding the cylinder(s).

            The block cooling diverters were good enough in the block that they were not obstructing the flow of water of where it should be going.

            At this point, this is irrelevant to check compression or chase cooling issues with embedded rust spots in the cylinder wall on the port bottom cylinder.

            If this wasn't a problem, I would have unbolted the midsection cover to allow the water for the TSTATs to fall to the ground, gotten the motor started enough to briefly get it going on the hose and turn it off. Then pull the hoses going to the thermostat housing.

            If the flow is strong, then that points directly to it being a thermostat issue.

            All the while checking the head temps with a temp gun.

            If the flow is weak on both sides, then there is a restriction in the block/exhaust housing cover area, blockage in the water tube, or a water pump issue.

            Likely need machine shop assessment of a reputable place nearby that does blind cylinder boring to see if the cylinders can just be cleaned up or some of them need to be bored oversized with new pistons.

            I'm not dumping +$150 in gaskets and replacement head bolts, which I'm sure those gaskets would have to be disposed of and re-purchased in doing an expensive engine re-build.

            Diagnose the most critical issues first, then figure out whether you want to move forward.

            Then address the successive issues afterwards.
            Last edited by havoc_squad; January 28th, 2019, 08:53 PM.


            • #21
              Head gaskets are pretty hardy, and should survive installation and test running without much risk. If mine, I would consider using some lapping compound to clean up the discolored areas in the bores, then resurface the heads and install the new gaskets. I would use the existing bolts in that fresh water motor. Torque to specs, and test run in a tank deep enough to cover the pump by six inches or so. After idling a bit, check temps -- if in the 140-150F range or below, I would conclude the t.stats were doing their job. Retorque after a couple of heating and cooling cycles.

              Measure the bores, as mentioned, and post the findings. Beyond possibly replacing t.stats, though, and correcting that small leak at the exhaust cover, I think at this point you might have a good runner.

              All IMO, of course.


              • #22
                Just to clarify, I am just replacing head bolts that have too much corrosion on them and re using the rest since they should not be TTY bolts.

                One concern while I wait for circumstances to get the accessible part of the clyinders measured, is very small debris captured by the piston rings.

                I seen a video of a scored cylinder possibly due to debris caught by the rings when a customer changed head gasket.

                Other than wiping good to pull the debris outside the cylinder when debris falls on the cylinder wall before the pistons move and ensuring mating surfaces are cleaned before re installing the head, is anything else just being obsessive/compulsive?

                I do know if debris does get lodged in the rings, the only way to fix is the powerhead comes apart.
                Last edited by havoc_squad; January 29th, 2019, 10:06 AM.


                • #23
                  Information update.

                  From where I live, there is not a single place recommended nearby that I can drop it off to get cylinders mic'd. Anything suggested that is good/recommended is probably a 2 hour drive or more on a business day.

                  Everyone I speak to says the engine machine shops nearby here are not worth requesting any of their services.

                  If its getting checked, the powerhead probably would have to be pulled, stripped down, and shipped.

                  From speaking with most of the service managers who are also master Merc/OMC techs looking the cylinder photos I had, they say to just clean up the surface rust, deal with the leaking gaskets, and if it has good even compression, run it.

                  Now, onto the other details:

                  I got the exhaust cover off without too much drama, but the actual exhaust manifold is a real bear. I can only get some leverage at the top left corner, but the manifold and gasket surface doesn't want to spread in releasing. I'm trying to avoid doing too much prying in one spot but I can't get any starting point anywhere else far enough to get it to pry off.

                  Any suggestions on getting the exhaust manifold off? Get a bunch of tiny flat screwdrivers and wedge it out?

                  Also, is there a way to tell the difference between powerhead bottom/base gasket leaking at the stern and the bottom of the exhaust manifold gasket leaking?

                  Regarding the thermostat, that infamous relief hole on the valve body was 100% clogged for a freshwater motor. If flushing isn't regularly done, that thermostat valve body will be the arch enemy of whoever owns a V4 crossflow.

                  I put the thermostats in my ultrasonic cleaner and warmed up the temp gradually. At 150 degrees F, the thermostat opened a small amount. At 160 to 165 degrees F, it appeared the thermostat was fully opened.

                  They don't look terrible and appear to be working, but I'd rather not have to deal with crossflow V4 thermostat fun again. Any reason to replace the poppet valve, grommet, or spring if nothing appears cracked, brittle, or too weak?


                  • #24
                    The cylinder heads should come off with a little gentle prying -- might try a rubber mallet to loosen. Thermostats should be 143F (5005440 for oem, 18-3543 for Sierra). IMO, the advice you received makes sense ("From speaking with most of the service managers who are also master Merc/OMC techs looking the cylinder photos I had, they say to just clean up the surface rust, deal with the leaking gaskets, and if it has good even compression, run it.") I would add, use a thin blade and scrape out the water passages you can reach when the heads are off.


                    • #25
                      Oldboat----I think the cylinder heads are off !


                      • #26
                        Thanks, Racer. My mistake.


                        • #27
                          Originally posted by racerone View Post
                          Oldboat----I think the cylinder heads are off !
                          Technically the heads are loosely bolted back on, but the exhaust plate/manifold is still on there really good.

                          There is a service proceedure for mis-reading a written description of a problem.

                          The steps are below:

                          Step 1, verify hot coffee is ready.
                          Step 2, consume 1 cup of it
                          Step 3, read problem description
                          Step 4, follow up
                          Step5, if your reply indicates lack of alertness and focus, repeat steps 1 through 4.
                          Otherwise if your reply is now correct, then proceed to step 6
                          Step 6, discreetly facepalm the moment.


                          • #28
                            (But keep a rubber mallet handy....)


                            • #29
                              Sign up today
                              Yay, victory over the exhaust manifold. No serious whacking required, but it did require me to buy one of those heavy duty prying scrapers that has a bend angle.

                              Now for the questions and possibly undesired answers I'll get.

                              I have two key questions:

                              1. Does there appear to be any damage/issue with the following area circled on the photo below, or is this just an aluminum casting imperfection?

                              2. I remember reading another forum topic that reported piston rings sticking when he had to take off an exhaust manifold for a 150 HP crossflow. The port sides on my outboard piston rings (#2, #4) are all perfect and wonderful, the starboard side piston rings (#1, #3) on the top ring and bottom ring are stuck. The piston sides look as normal and usual as expected and I don't see any visible carbon buildup around the piston ring groove.

                              Is this another situation of powerhead separation required to remove piston and clean the ring grooves? Or should I try doing a OMC engine power tune can procedure first, and then check it via the bypass cover to see if it is bad enough to require piston ring removal?
                              Last edited by havoc_squad; February 9th, 2019, 02:14 PM.