1996 Rinker Rocket Merc 120XR

[Sharkbaite]

I recently purchased this boat with the Jet Drvie system and after some toying around and replacing broken parts I got the boat running, but I can hear a thumping sound that will either cause the motor to momentarily stall or die out completely, I did find through some normal issue's that the gear oil was replaced by water in the Stator housing, I fushed it out and reserviced with about 3.4 Ounces of gear oil hoping this was part of the cause, the stator and wear ring was in good shape and normal end play on the output shaft and slop is normal. I am about to pull the motor out so I can finish working on replacing some hoses and also to replace one of the fuel recirculation elbows that I broke while changing the hose.

What I am looking for is if anyone else has had this issue or knows what could be causing the thumping sound. its almost like either a bad bearing in the output shaft connection to the jet drive assembly or the worse yet, a bad rod bearing in either #3 or 4 cylinder.

 

[sixfigures]

Rod bearings are pretty easy to check, remove all your sparkplugs . Rotate the engine by hand using the flywheel going in one direction ONLY to bring up the first piston to top dead center viewing it through the sparkplug hole, as soon as the piston starts to go down, past top dead center, stop moving the flywheel and use a screwdriver to push on the top of the piston, it should feel tight, if you feel or hear a clunk when you push the piston, you can bet you have a bad rod or wristpin bearing. Do this to each piston to check the end play of the rods.

 

[Sharkbaite]

ok after going through the lubrication system, I found water had replaced the lube in the Stator assembly, cleaned and reserviced oil 3.4oz of lube, then restarted the motor and still get same noise, although this time it it sheared the moon key on the flywheel while starting due to the thump/thud noise. I did check the cylinders for endplay to check for wrist pins and or rod bearings had play and did not notice any....

I just pulled the motor just so I could service it easier with it out of the boat, and verify the engine without being attached and by turning it by hand I could not hear the noise, I then spun the input shaft to the lower drive and still no noise. I am curious if a fouled plug could cause my issue as well.
I have just finished reservicing the lower drive assembly and found it was over serviced by about 6 oz of fluid, required 18.6oz and I drained out about 24oz if not a hair more. reserviced to correct specs.

Waiting on Orings to come in, ordered from several different sites as not one place had all the parts I wanted in stock.

Any input????

 

[sixfigures]

Shearing the key is strange unless the flywheel was loose, Timing could be off, did you check the magnets on the inside of the flywheel ? some may have come loose and changed position messing things up, the thumping could be a cylinder not firing .

 

[Sharkbaite]

brand new flywheel, its possible it may have come loose as it is new. I'll retorque it after I put the motor back in and set back on, I have the old one sitting on the motor now since I didn't want to damage it while pulling the motor out. I did notice one of the plugs showed more wear then the rest and thats why I am going to replace them just in case, Timing is pretty close, hard to really tell correct spot as the motor sits inside the boat and not a normal outboard configuration where you have full 360 view. Timing was reset after replacing the Flywheel, Stator and Trigger assembly as they were damaged when magents flew off flywheel when previous owner had the boat.

 

[sixfigures]

Sounds like the engine has all it needs mechanically so if the reeds are good and the fuel is ok and the ignition is correct it should run.

 

[Sharkbaite]

put it all back together last night and purged fuel and oil lines, put it on the hose this morning and pissed off the neighbors, but got her running and sounds better, but smokes ALOT, I do know that at idle the ratio is 100/1 fuel oil ratio vs 50/1 at WOT, but I see alot of unspent or oil coming out of the exhaust while at idle and a sheen on the water after coming down from WOT. I ran her in the water as well this morning. I know its the oil as its black in color and spits with a sputter of the engine, I am thinking I might be too rich and that may be one of the reason for poor performance. there is hesitation in the throttle when I advance it to quickly and that could be a carb issue, but seeing the oil and smoke coming from it makes me look like I work for the local mosquito control people as I can fog up the neighborhood, and the local police volunteers commented about my oil slick in the water.. haha

Any thoughts?

 

[Sharkbaite]

Now being that I have it back at the house and on the hose, I turned on the water only and I can see the oil coming out in droplets which would be what was left over as cleared after about a minute until I restarted the motor to fluch it that the oil started coming out again. I think maybe my oil pump is the real culprit. Causing me to use to much oil and whats not burned is being pushed out the exhaust.

 

[sixfigures]

time for premix

 

[Sharkbaite]

I just did that, removed the oil pump lines and ran a straight line direct to the fuel pump, did a 50:1 premix to about the 5-6 gallons I had in the tank, and it runs alot better, but I did have condensation building up on the upper carb which indicates a leak around the gasket. I will replace that this am and put it back on the hose and retry, still need to redo the idle air screws on both carbs again since I have the air leak.

Any other ideas, or does anyone know of the part number for the blocking kit to remove the oil pump and shaft from the engine since I won't be using them.
its a 96 Mercury/Force sportjet 120XR

 

[sixfigures]

Sadly the sport jet is pretty obsolete, so I don't know where you can get parts for those, I had one myself many years ago. be very careful of the rectifier, if it goes bad the second you turn off the engine it will fry the ignition brain. people thought replacing the windings with the newer style would fix that but I can tell you it didn't fix anything and when I replaced the windings with the new stator it ran once and blew the new brain , after finding the culprit RECTIFIER everything worked just fine, but for safety I installed a circuit shield to prevent it happening again. I also had issues with trash in the fuel lines clogging the needles and not allowing proper fuel to the carbs. on your oil line you may just do a loop of hose from the in fitting to the out fitting fill the hose with oil and leave it like that, the oil in the hose would circulate and lube any moving parts.