01515D2F-CCA8-44F4-BD38-ADF8FB02EE29.jpegBCA06C65-22E8-4408-A51C-315368093429.jpeg46A83289-16A0-445A-B91E-D1BDED0D1374.jpegEng s/n 0G843442. The retaining bolt for the belt tensioner backed off causing belt to run off the lower edge of the pulley and generated a good amount of rubber “dust” particles. I replaced the tensioner pulley & belt and also removed the air handler and reeds, and cleaned all of the debris I could find from the handler/reeds and everywhere on the motor and interior of the hood & cowlings. I ran a compression test and top four cylinders were about 115 with 5 & 6 coming in at 110. I’m 85 miles from the nearest Mercury dealership so I used the shift handle to run the oil prime procedure. Yeah I know that also put it in a 4-hour break-in cycle but I have a new set of NGK plugs ready to install afterwards. While reinstalling the tensioner, I noticed that the plastic spacer bushing protrudes about 3/16” past the bronze center hub that the retaining bolt passes through ( see attached picture.)When I torqued the bolt, the entire tensioner was basically locked down and could not pivot.. I checked the manual to see if I had misplaced or lost a spacer but what I have matches the factory service manual and parts catalog. If I backed the retaining bolt off maybe 60-70 degrees, the spring-loaded tensioner could turn freely... but then that bolt wasn’t torqued to specs. I ran it on the water muffs and it ran & sounded good, so I decided to take the boat out for a short test run with the bolt “semi-loose.” It jumped up on plane and ran well for 15 minutes so I ran it at idle trolling for maybe 10 minutes. Shut off for several hours and trolled with the kicker. Fired up the big motor for a short run back to the dock and it was a real pig coming out of the hole and getting on plane. Normally can run about 50 mph loaded but wouldn’t get past 35 now. Perhaps being in the break-in cycle fouled the plugs already but it wasn’t really misfiring....just ran like a 90-horse motor instead of a 200. I also saw the check engine light had came on it stayed on solid with no beep tones. Killed the engine and started it up again, and the light came back on within 3 seconds.
Took the hood back off today and found the loose tensioner retaining bolt had already backed off about 1 round (no surprise there) but the belt was still on all of the pulleys. Inspected the air handler, VST box, etc. to make sure I hadn’t left any wires or hoses loose; everything was intact up front. Per the service manual, engine lamp with no beep could be the coolant temp sensor (maybe):MAP sensor, air temp sensor, ignition coils,or injectors. The wiring connections and tubing for these components had not been disturbed in the initial repair and all of the connections and wires looked ok.
so 2 questions: 1) what could have gone wrong with the tensioner? it worked before the bolt backed out, like if I put a ratchet in the square hole and pulled on it, it pivoted against spring pressure and the spring promptly pulled it back tightly on the belt. All of the parts shown in the manuals are there and it looks like there is only one way you can install the spring correctly.
2) I’m not certain I found the coolant temp sensor. The wiring diagram shows a single brown/purple stripe wire. I read on another post the sensor is close to the port side thermostat but all I found was a sensor with 2 plain brown wires. Even with low power, I didn’t detect a misfire. Wouldn’t claim it was running great by a long shot but I calso can’t say it was missing like a coil or injector should cause.
Expert assistance would be greatly appreciated.
see pic. The inner plastic spacer “bearing” is longer than the center of the tensioner central pivot, so when the retaining bolt is torqued, the plastic spacer is compressed between the tensioner and the mounting surfaces.
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