115 Mercury rattles and will not engauge in reverse

[cjdeayala]

Hello All,

I have a 1990 115 Mercury outboard motor on an 18ft wellcraft that starts and runs great. The motor has always rattled while idling in reverse, but would stop rattling and work in reverse after giving it more throttle.

After fishing this morning i hit a submerged board or log at cruising speed on the way back to the ramp. After hitting the log the motor makes a louder rattling/metal clanking noise (only when put into reverse) and will not engage in reverse. The boat runs perfect in forward and neutral.

Any suggestions? I am by no means a mechanic but am mechanically inclined and have replaced other parts on the motor.

Any help is appreciated. Thanks!

 

[TD_Maker]

Re: 115 Mercury rattles and will not engauge in reverse

It really sound like a cable adjustment to me. The cable adjustment wheel (on the motor) may need to be adjusted to allow the gearcase to fully engage F-N-R I would start here.

 

[cjdeayala]

Re: 115 Mercury rattles and will not engauge in reverse

Thanks for the quick response. I'm going to look at the shifter cable when I get off this afternoon. Any suggestions on how to adjust the cable?

 

[TD_Maker]

Re: 115 Mercury rattles and will not engauge in reverse

Yes, the cables (entering the motor) are threaded. Once the cable is loose, you should be able to find absolute neutral just by moving the shift lever by hand. Once you find this position, adjust your cables by rotating the adjustment nut accordingly. Just make sure your shifter box is in neutral as well. Obviously, when in neutral, there should be no gear noise or "rattling" at all.

 

[cjdeayala]

Re: 115 Mercury rattles and will not engauge in reverse

TD_Maker,

I adjusted the shifter cable and went to the lake to see if it had made a difference. Unfortunately, I still have the same problem. I tried pushing the shift lever by hand to see if it needed more help getting into reverse...still same problem. I tried with the motor off and again with the motor on and with the throttle lever in reverse.

Any new suggestions? I am hoping this is a fix i can do myself and not have to resort to a mechanic($$$).

Thanks

 

[TD_Maker]

Re: 115 Mercury rattles and will not engauge in reverse

There is a guy on here called: Oldman 570 He is a Mercury Guru, and he can probably point you in the right direction.

 

[oldman570]

Re: 115 Mercury rattles and will not engauge in reverse

Any rattling in the motor when it is in reverse only can be caused from several things. Loose bolts, worn reverse locking connections, worn lower unit clutch dog or parts in the LU. A good check over of all the easy to get at items should be done first. Draining the oil/ grease from the LU and looking for water intrusion and any metal partials on the drain plug and in the oil will be a indication of seal leakage or worn parts and can be the cause. A prop that is not in good shape might also cause vibration in reverse. If more than the prop shaft, carrier bearing have to be removed, then it should be done at a good shop as special tools are needed to get everything set back to specs. It will cost more to replace a LU that is not done correctly than having it looked at at a good shop. JMO
Oldman570

 

[TD_Maker]

Re: 115 Mercury rattles and will not engauge in reverse

See? What did I tell you? Oldman 570 is THE MERCURY MAN!

 

[tracyinks]

Re: 115 Mercury rattles and will not engauge in reverse

Any rattling in the motor when it is in reverse only can be caused from several things. Loose bolts, worn reverse locking connections, worn lower unit clutch dog or parts in the LU. A good check over of all the easy to get at items should be done first. JMO
Oldman570

I hate to start a new thread and re-ask a question...... Let me preface this post with I have been around boats my entire life and owned a few as an adult, but NOT a mechanic. I have a BIL and a dad that are very mechanically inclined but Outboards are not something they tinker with. My knowledge on them is lower units go OUT and cost about $800 to have them fixed at the marina IF you can get it in......... anyway. This thread caught my attention because of the Rattle and Not engaging title......... sounded familiar.

My Mercury is 1993 75 HP, and last summer the reverse went out (reversed out of the dock, but while trying to use it to redock it wouldn't work) It was around the same week/ end a guest captain grounded/swamped my pontoon and we had to slam it in reverse to get it out of the mud and pop the front of the boat back above water........ it wasn't immediate so I never really associated the two events until reading this forum. Last summer my BIL checked linkage, and it seemed to be fine. Over the winter my dad tried to dive into it to figure out the problem he said it went into reverse and he didn't know what he did. So to the lake we went. The motor ALWAYS starts like a champ, and it WILL go into reverse but it makes a loud rattling noise and it the amount of "pull" backwards it has is about as strong as a trolling motor........ increasing the throttle increase the sound but not the pull. I would say that the answer above needs to be printed and give to both my dad and BIL, but I wanted to make sure I threw out the different size, year and the fact that it DOES shift to reverse. Thanks in advance!

Tracy

 

[Dgfrank2]

Re: 115 Mercury rattles and will not engauge in reverse

Hi you all !!

Im having the same problem with my Mercury 150 efi 2005 , outside the water it engages reverse but in the water just make a noise and does not works ,any help would be appreciated

 

[Texasmark]

Re: 115 Mercury rattles and will not engauge in reverse

The shifter on a Merc of current vintage at least is a cam operated by the shift lever and a sliding gear locked to the rotation of the prop shaft called a clutch dog. The dog is operated by a pin of sorts, a spring, and 3 ball bearings for spacing...on mine and my old tower anyway.

The shift cam has 3 detents, each a different distance from the pivot point. The "pin of sorts" rides in these cam detents. The spring and balls inside the front end of the prop shaft move the dog through 3 positions depending upon the position of the shifter cam....F N R.

F has an overrun clutch for use when the engine runs slower than the prop....like when you are coming off plane and coming into the no wake zone. It ratchets when you turn the prop cw and locks to the crankshaft when turning ccw. N has the clutch positioned between the F and R gears which are constantly rotating due to their positive connection with the drive shaft pinion gear and the prop rotates freely.

R is a different critter. It has either 3 or in later engines, like my '02, 6 vertical sided cogs and slots; cogs in the rear of the shift dog and slots in the R gear. The reason (opinion) Merc went to the 6 count was because of pre-mature failures of the 3 count units. If the edges of the cogs and slots become worn, from normal wear or sloppy usage, the spring loaded dog can't compete with the rounded edges when power is applied and will slip out of the groove. This causes a loss of propulsion and funny noises.

The prop shaft can be removed with no special tools or training. If you have the later model lower unit which came with the conversion from multi cylinder engines to the 3 cyl engines back in the '80's time frame it is a lot easier to remove the rear carrier bearing and prop shaft with the dog and all. If you have the old design lower unit with the spanner nut that is screwed into the housing and about 4" in diameter it is a chore as these are usually really corroded and almost impossible to remove.

If you choose to fix it yourself, get a manual to help you through it. If you have any kind of mechanical dexterity you can do it. Seloc manuals are sold and rented on the site and are a good reference.

Mark