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

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

    1990 Johnson 90hp VJ90TLASB model.


    After doing a VRO delete, carb rebuild, impeller replacement, throttle sync per service manual, and addressing minor time consuming issues that came up.

    I was finally able to get the motor running today and seemed to do fine on the muffs, except that there was too much play in the throttle cable in and idle was much higher than I was expected. Was probably about 1500 to 1900 and the gauge wasn't working on the dash.

    I had the cover off, pushed the throttle arm back down to the idle stop to take up the slack and things settled down to probably 1000 rpm. (When the engine was turned off, I adjusted the cable lash/takeup and resolved that but didn't get to verify that fixed that issue.

    Just for saying purposes, I did what the manual specified on the throttle arm to verify the carb sync roller is moved to where the arrow is pointing in the middle with the butterflies closed on the carb and that the carb arms do NOT move.

    Not knowing the history of the motor, I had an infrared temp gun out checking the cylinders as soon as the idle stabilized.

    I had a full strong tell tale stream and it appeared a reasonable amount of water was coming out of the exhaust hub.

    So, I watched the temperatures climb on my temp gun, and the result was:

    Port cylinder head stayed steady around 157 to 160'ish degrees F

    Starboard head increased to about 180 to 189 degrees F. Soon as this stayed this amount more than about 10 to 20 seconds I think, I shut the engine off and did not restart it. There was no alarm that went off and I did verify the overheat buzzer worked on the control box per the service manual on the starboard side cylinder temp sender wire.

    Also, I have a small leak around the bottom port side of the exhaust cover plate likely where the gasket area is, not a leak around the port cylinder heads.

    So, my questions are:

    1. Is there any situation where I may have prematurely assumed an issue here but there is not?

    What is the best procedure on this model of motor since the thermostats likely require a powerhead removal to access? Remove the starboard cylinder head and look for issues first, then if nothing is found have the powerhead pulled and get the thermostats and power valves replaced?

    Once the issue is narrowed down for the starboard overheating, replace all applicable exhaust housing gaskets?

    2. Was the throttle/carb linkage synch procedure performed the correct way, or was I reading it wrong? Just for saying, I have not had time to verify idle timing, nor do the Joe Reeves timing steps for non-running max timing test. None of that has been disturbed by me, just saying since it's "new to me".

    3. Tach was acting wierd, barely moved and sometimes would barely show a reading. Was too busy concentrating on engine sound, getting the idle down to normal, and checking engine temp. How is the outboard tach tested on instrument gauges?
    Last edited by havoc_squad; January 15th, 2019, 07:50 PM.

  • #2
    Anything at and over 160F is too hot. You might have more success running in a test tank -- can't tell much about the water pump while running on muffs. If it's a salty, may be time to remove the heads and scrape out water passages.


    • #3
      The Previous owner boat/motor originally came from Midwest US and I'm in a fresh water only area, so highly doubt salt water corrosion given how well all the fittings and metal is absent of corrosion.

      If there is blockage, it must have been a very dirty lake the PO used it in or an Impeller chunk 10 years old.

      I'm leaning towards the following possibilities:

      1. Thermostat on starboard side is sticking closed and maybe winter water pressure isn't enough to keep up on the hose/muffs.

      2. Some issue with the water pump sucking air, impeding water flow? I noticed no how much I tried to align the water pump housing with a new kit (I double checked the kit part #), the hole for the drive shaft seemed very slighly off center.

      The water pump kit directions contained in the kit were followed 100%. No spare gaskets/o-rings were left out and the housing was torqued to spec.

      3. Blockage in the water jackets. If this is suspected, what's the best recommended method for checking passages, low PSI compressed air or short moderate bursts of water from a water nozzle?

      So from your suggestion, I'm seeing that I might need to a run to the lake boat ramp to test the water pump and the engine cylinder temps using a temp gun. That is probably much easier to arrange than buying a plastic trash can and fill/empty it multiple times.

      Would it be best to wait and replace the exhaust housing gaskets then do the test, or do the test first?

      Just trying to avoid being a parts changer and have a ton of extra parts that I don't need.

      At minimum I know I need inner and outer exhaust cover/plate gaskets. I could also get the cylinder head cover gaskets to inspect those.

      What I'm more wary about is the necessity of buying the head gaskets now and find out later I don't need to remove the heads.


      • #4
        The water pump is off center !----It has to be in order to work properly.-----Look into the parts called " water deflectors " they are found after taking cylinder head off.-----They guide water around the block but can also block the flow.


        • #5
          +1 on the deflectors. They’re just sections of rubber tube jammed into the cooling passage and they swell up over time, even in fresh water, creating dry hot spots. Had this issue on mine even though PO had the block re-bored by a shop... no one bothered to replace the stupid deflectors and motor overheated stbd side, even though water circulation seemed strong. Wish I could go back in time and spend the $ on gaskets but now cylinders are scored. Cant diagnose them until heads are removed, pretty simple job.

          I did my t stats without removing the powerhead, but that was a helluva of a job.


          • #6
            Originally posted by racerone View Post
            The water pump is off center !----It has to be in order to work properly.-----Look into the parts called " water deflectors " they are found after taking cylinder head off.-----They guide water around the block but can also block the flow.
            I'll clarify, the previous water pump housing drive shaft hole was much more centered than the new water pump housing I installed.

            So, it's a little confusing where I read: "it has to be in order to work properly".

            So, it looks like removal of head and the head cover is in order on both sides. Any helpful reason to do a compression test before I pull the heads off, or a waste of time based on my data points/description of what happened.


            • #7
              All water pump impellers on outboards are offset.---This is done so that volume between vanes changes.------They work as a positive displacement pump at low speed !!


              • #8
                Information update, with photos of the work attached below:

                I've pulled the Starboard cylinder head cover and the cylinder head. They were as expected, marvelously clean and clear with no blockages found.

                The head cover gasket and the gunk trapped behind the gasket to the cover made more mess than what was found.

                Both cylinders "appear" normal with visible cross hatching present all around. The only area of possible concern is a barely visible light rust like surface ring at the top/lip of the cylinder where the piston rings do not reach.

                The bottom most bolts gave me some concern about breaking them, but thankfully that never happened.

                The diverters "appear" to be the correct size and shape, blocking where they should be.

                Unless anyone can point anything out otherwise, it seems its put it back the way it "should be". Remove and replace Exhaust cover inner/outer gaskets to fix that leak, then determine method of access for TSTATs.

                Does replacing the head gasket require all new head bolts? Some I do intend to replace for corrosion/condition reasons. I do not remember seeing that explained in the manual where it says that replacing all of the head bolts is required.

                Cylinders have already been wiped clean, sprayed wall with fogging oil, and cylinder head & cover temporarily installed loosely to keep moisture and crud out. It's going to be a couple of weeks before I make any progress on this.

                So, how problematic is the work around loosen things up to take off the thermostat housing without having to pull the powerhead?

                I really really do not want to do the cut the cowling hack to access them and fabricate something to cover that hole.

                If powerhead needs to get pulled, I'll have it pulled by a trusted service shop nearby. Don't have enough room for a cherry picker right now and I'd rather not attempt pulling a powerhead without another person around to assist.

                Last edited by havoc_squad; January 20th, 2019, 02:30 PM.


                • #9
                  To my eye, there is evidence of some water intrusion at the lower cylinder. Should be able to clean and correct by resurfacing the cover and regasketing -- would replace the deflectors as well. Bet on some warpage if there was some overheating.


                  • #10
                    If I recall, there was spots of black and rust on some of the top necks of the bolts on the mid bottom bolts, I think mostly on the left side.

                    At some point in probably did overheat and blow through the top of the bottom cylinder.

                    What is the best cost effective straightedge for checking warpage? Getting a typical steel square/ruler, or find a reputable machine shop?

                    I seen a cheap steel straightedge used with feeler gauges to check the warpage on a head being serviced on Dangar Marine.


                    • #11
                      Every head I have seen / worked on was warped.---------Use sand paper / lapping compound and a piece of glass to correct the flaw.-----Takes just minutes and a bit of work.----Inspection of thermostats is not hard on the 90 HP version.-----Salt water motor ?----Then all bets are off.


                      • #12
                        ^^agree, I use wet/dry sandpaper, used wet (full sheet will stay in place on the hard surface if wet). If a salty, will require scraping out deposits from water passages, just routine with use in salt water.


                        • #13
                          Regarding t-stats, it is possible to change them out w/o pulling powerhead or cutting the cowl.

                          Remove the plastic skirt thing around upper midsection and remove hardware holding the lower pan in place. This will let you move it around to squeeze your hands and tools in there.

                          Remove the hoses, then the t-stat assembly. You'll likely need a u-joint wrench and a bunch of different extensions. A dog-legged wrench may also be handy.

                          Clean everything, ensuring all holes are free of buildup. I followed someone else's advice here and opened the factory bleed hole in the valve body up to .060 and notched the plastic relief valves a tiny bit for better bleeding of air.

                          Trace and cut holes in a piece of plywood for the two stats using the inner gasket as a guide. Assemble the new stats, gaskets and housings on the workbench, using a very light coating of gasket sealer on all mating surfaces - careful not to clog any bleed holes. Place the wood on top to make a "sandwich", letting the tops of the stats poke through the holes. Now clamp the assembly very tightly to compress it all in there, and let it sit overnight.

                          When dry, unclamp it and remove wood, hopefully it stays together. Use wire ties to hold the plastic relief valves to the sandwich. Put the springs in the motor. Put bolts into the sandwich, and position it on the springs.

                          To compress the springs, I used a really long piece of wood and wedged it between the housing and pan... had to futz with it for each bolt but it worked well. Some folks use a stud (with no head) in the center bolt to line it up, then remove it with pliers once the other two are in. Another set of hands helps a lot.

                          Once you have the two outer bolts barely started, you should be able to clip the wire ties and slide them out. Torque to spec etc.


                          • #14
                            Since the PO very likely overheated the powerhead from the data about the starboard side, I'll be pulling the port head & cover for inspection before I work on head resurfacing and TSTAT housing investigation.

                            No point in ordering parts if there is a major defect found that wasn't visible thru the spark plug hole.

                            I did see that TSTAT job forum topic and have it bookmarked for future reference.

                            One of the first things I bought in prep for working on outboard were 1/4, 3/8, 1/2 drive swivels and various length extensions.

                            I knew they would be almost mandatory.
                            Last edited by havoc_squad; January 24th, 2019, 08:34 AM.


                            • #15
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                              I'm back with the results of the port cylinder head removed.

                              It appears the bottom cylinder of the port side had somewhat more moisture contamination than the starboard or was less fortunate.

                              The top one looked as expected for a normal cylinder with cross-hatching intact.

                              Not sure if it was the head gasket being on its last leg, or through a small water leak in the exhaust manifold.

                              That gasket was completely toast and glued to the engine head.

                              I can't feel anything different when I move my skin over the area in the attached photo.

                              The picture of the area of the yellow circle was the most visible and rust colored spot of the entire cylinder.

                              The parts northeast of it going up the cylinder looked if there was rust spots, they got worn away from running/use.

                              Is the rust on this bottom port cylinder bad enough it requires powerhead removal and re-hone of cylinder or oversized?

                              If the rust is not deep/problematic enough, is there an easy method to use to safely remove it without gouging the cylinder surface? I'm aware brass is soft, but is it soft enough for rust removal on a cylinder wall?

                              Also, one side item was there was some significant residual water at the bottom of the cooling area passageways of the port cylinders.

                              Even though I previously lowered the lower unit completely down to the trim limit after test running it for the first time on the hose originally to ensure things drained as they should.

                              Should I be worrying about the need of doing an inspection for freeze damage to the powerhead?
                              Last edited by havoc_squad; January 26th, 2019, 01:50 PM.