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Merc 90 hp forward reverse stiff when running

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Mercury 90hp

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1979 oil injected 90hp merc difficult to put into forward or reverse when running. When engine is off it moves freely into forward and reverse. Idling is normal. No changes that I have noticed.

What can cause this? It seemed gradually worse over 3 fishing trips. Almost didnt make it back last time.
 
An inline 6 cylinder ?-----A 1979 with oil injection ?------First thing I would do is check the gear oil in lower unit.
 
Are you shifting into reverse when the motor is not running? If so how often? This can damage the shift mech as has been mentioned before on this site.
 
In reply to the first response,
thanks,

yes its a 1979 "oil injected" and Im glad I could show you something new for your knowledge base.
Its an outboard motor and getting it off the "permanently" moored 35 foot house boat to check the gear oil is difficult.
My last option is to remove it and check things like that. It doesnt tilt up enough to expose the lower end.

second response,
thanks,

part of my trouble shooting was to remove the shift cable and manually shift with my hand at the motor connection point with the engine not running. It moves freely. So why would it be so stiff when the engine is idling?

If it was a gear oil issue it would be stiff even with the motor not running.

If putting the engine in gear with the engine off will damage anything then no motor is worth having as this is completely retarded.

I dont believe putting a outboard motor in gear manually while not running will damage anything.
Dog clutch is made to be "slammed" into gear with moving parts. Its some of the hardest metal made.
EVER single out board Ive ever heard put into gear has that clunk sound. Thats to gears being put together while one of them is moving.

Its designed that way.

Back to original question....
easy engaging movment when not running, very stiff movement and engaging when running.

Difference? engine running / not running....... idling slow and normal when running.

very hard to twist vertical rod that goes to dog clutch when running, when not running it twists very easily.

what can cause this...besides oil...cause like I already said....not the problem.
 
Sorry ----but you have a lot to learn about the shifting of outboard motors !!!.-----If it is an inline 6 with the " autoblend " unit you should take that unit and heave it as far over the fence as you can.-------Look , listen and learn.
 
Last edited:
Mercury 90hp said:
In reply to the first response,
thanks,

yes its a 1979 "oil injected" and Im glad I could show you something new for your knowledge base.
Its an outboard motor and getting it off the "permanently" moored 35 foot house boat to check the gear oil is difficult.
My last option is to remove it and check things like that. It doesnt tilt up enough to expose the lower end.

second response,
thanks,

part of my trouble shooting was to remove the shift cable and manually shift with my hand at the motor connection point with the engine not running. It moves freely. So why would it be so stiff when the engine is idling?

If it was a gear oil issue it would be stiff even with the motor not running.

If putting the engine in gear with the engine off will damage anything then no motor is worth having as this is completely retarded.

I dont believe putting a outboard motor in gear manually while not running will damage anything.
Dog clutch is made to be "slammed" into gear with moving parts. Its some of the hardest metal made.
EVER single out board Ive ever heard put into gear has that clunk sound. Thats to gears being put together while one of them is moving.

Its designed that way.

Back to original question....
easy engaging movment when not running, very stiff movement and engaging when running.

Difference? engine running / not running....... idling slow and normal when running.

very hard to twist vertical rod that goes to dog clutch when running, when not running it twists very easily.

what can cause this...besides oil...cause like I already said....not the problem.
Click to expand...

I am afraid that I would be the one to tell you that this "shifting into reverse with the engine off can cause damage" is a real thing. I did it and bent the shift rod, wound up taking the lower unit apart to replace the shift cam also. So unless you get very fortunate and the reverse dogs just happen to be lined up right you will bend the shaft. Of course it can be done if you either have someone to turn the prop by hand while you put it in reverse or do like I have and pull the shifter only part way back a little at a time then go back and turn the prop yourself till you feel the dogs mesh.
 
I guess I should mention why that is the case. The shift collar is spring loaded to push the gear into forward and the shift cam just pivots out of the way when forward is selected. To get reverse the cam pushes the pin in the shift clutch rearward against the spring and it winds up being in coil bind, a solid no give assembly pushing against the reverse gear. If the dog teeth happen to be butting up against each other there is no way for the gear to engage and something has to give. It happens that the shift shaft is the weakest part in the lineup and so it bends when the shift lever is pulled hard enough.
 
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