15 hp 1994 Merc lower unit gear shift trouble

[morningtide]

After replacing the flywheel, I've found that the engine runs well but I've lost neutral and reverse. I speculate that blocking the prop while torquing the flywheel nut, has caused some damage in the bottom end. The bottom end is stuck in forward, while the tiller handle through to the lower end shift rod travel through the FNR positions ok. Problem with the shift cam / cam follower / spring perhaps?
Does anyone know how to remove the prop shaft without having the special tool which manuals refer to?

 

[carholme]

Re: 15 hp 1994 Merc lower unit gear shift trouble

morningtide;

Just on the offchance, did you have the lower unit removed while you were working on the engine?

Gerry

 

[morningtide]

Re: 15 hp 1994 Merc lower unit gear shift trouble

No. Only lower unit activity was a wood block in the prop while torquing the flywheel nut, tiller handle twisting, and prop removal for running in the test tank.

 

[carholme]

Re: 15 hp 1994 Merc lower unit gear shift trouble

Well, in my mind there would be a heavily increased torque applied to the drivetrain depending on whether it was in gear or not and if the cylinders moved, while the prop was held in place. Any movement of the cylinders while in gear, would be like using a Sweeny wrench, magnifying the torque on the driveshaft.

Always use a flywheel holder if you have the lower unit installed.

If it were mine, I would drop the lower unit and check it in each gear for correct prop operation and proceed from there.

Gerry

 

[morningtide]

Re: 15 hp 1994 Merc lower unit gear shift trouble

What would that demonstrate that I don't already know? Wouldn't prop shaft removal be more direct to the most likely problem?

 

[carholme]

Re: 15 hp 1994 Merc lower unit gear shift trouble

What would that demonstrate that I don't already know?

Well, sorry for taking your time, you obviously know what the problem is so I'll leave it up to you.

Gerry

 

[morningtide]

Re: 15 hp 1994 Merc lower unit gear shift trouble

Not really. I simply don't know what advantage dropping the leg would have, over removing the prop shaft / gears. Isn't the gear housing where one can view the shift cam operation?

 

[sxmerc]

Re: 15 hp 1994 Merc lower unit gear shift trouble

Gotta' drop the lower unit to fully disassemble anyway, so why not check operation off of the motor prior to tearing it apart? You may have broken, bent, or damaged the shift shaft by using the gearcase as a flywheel holder.

 

[Mi duckdown]

Re: 15 hp 1994 Merc lower unit gear shift trouble

What would that demonstrate that I don't already know?

Well, sorry for taking your time, you obviously know what the problem is so I'll leave it up to you.
Priceless

 

[morningtide]

Re: 15 hp 1994 Merc lower unit gear shift trouble

Just an FYI wrap, in case others have a similar issue with losing neutral and reverse.

Water found in the gear case (after many years in a salt water environment), along with broken off end of shift cam . Light corrosion found on gear assembly, likely causing the cam follower to bind, breaking the cam upon attempt to shift out of forward. Heavier corrosion on aluminum threads means the housing is toast.

Lesson learned: Even if your gear lube looks ok each time you change it, occasionally spin prop shaft out to ensure that the seal is not being compromised by corrosion, and the threads don't seize.