Mercury 500 gear engagement

[brad1756]

Hey guys, I got a 74 model that won't go in gear. Last week on launch, reverse wouldn't engage but forward would, after grinding a little and requiring a little more forward movement of lever than normal. The next trip, forward wouldn't engage either. Back in the early summer I had replaced the prop with one off a spare motor and I had to use a different washer/spacer to get the new(different) prop on.( I don't know if this is relevant, just telling all I know of the circumstances for troubleshooting purposes) It seems like I notice just a little more end play in the prop as I pull the prop forward and back. I have checked the control box and cables, and it seems like there is sufficient movement of the cable ends at the motor. What would your educated guess be as to the cause of this?

 

[emckelvy]

Re: Mercury 500 gear engagement

Pull the prop and check the threaded retainer (Merc calls it a "cover") which holds the reverse gear/propshaft bearing carrier in place. It's possible the retainer has unscrewed and allowed the bearing carrier to move rearwards.

This could be causing the increased end-play you feel in the propshaft, and the shifting problems.

But before tearing into the lower unit, try disconnecting the shifter cable and see if you can manually shift into gear. If so, you may have worn parts in your control box.

If it still won't shift into gear manually, I'd suspect something wrong with the lower unit.

If the gearcase cover has come loose, you can fix by draining the gearcase, then unthreading the cover all the way; pulling the bearing carrier out; cleaning up all the parts, and re-sealing the bearing carrier along with a new O-ring. Use Permatex Aviation-type No. 3 gasket dressing on the bearing carrier and the threaded surfaces of the gearcase/retainer. This'll keep salt/corrosion products out of these areas.

Here's a parts diagram for your information:

http://www.mercruiserparts.com/Show...desc=GEAR+HOUSING+ASSEMBLY,+COMPLETE+(PAGE+2)

One last thought, if the reverse lockout mechanism (the part that hooks down onto the tilt pin) is binding up, it'll cause shifting problems. So be sure that the reverse hook is free to move on/off the tilt pin.
HTH & let us know what you find........ed

 

[Chris1956]

Re: Mercury 500 gear engagement

In addition to what Ed said, check the gear oil in the gearcase. Perhaps it leaked out, or water leaked in.

 

[brad1756]

Re: Mercury 500 gear engagement

Thanks for the replies so far, good stuff. I'll be away from home for a couple of days, but I'll get started on it when I get back. Can I take the parts out you mentioned without special tools? I have a fair amount of mechanical ability, but absolutely zero experience with lower units.

 

[emckelvy]

Re: Mercury 500 gear engagement

There's a special tool sold by Mercury which fits the internal 'cogs' in the threaded gearcase cover, for removal and reinstallation.

If you're handy with a welder, you could probably cobble one up with some pipe and flatbar welded to the sides of the pipe to engage the 'cogs'. Weld a nut on the free end of the pipe to take a suitably-sized socket.

If the ring is loose you may be able to carefully spin it out with a flat punch but be careful not to damage anything.

When reinstalling there's a considerable amount of torque (110 ft-lbs) applied to the cover in order to seat the bearing carrier & keep it from backing out. You likely won't be able to apply enough force without some sort of tool, home-made or otherwise.

HTH...........ed

 

[brad1756]

Re: Mercury 500 gear engagement

I guess I'll have to tell this on myself, so I can accept it and move on. LOL I am normally a very maintenance minded guy, but I've let the lower unit slide. My only excuse would be that I never saw any oil spots or anything. ANYWAY, no oil in lower unit, only water. I did take the prop and washers off, and it appears that the cover(?) or inside nut, for lack of a better term, has backed/been pushed out as the threads look a little rolled. It seems like it is plastic?? It looks like, at the very least, the unit will have to come apart so I can clean every thing up. I have read here somewhere about needing to either keep the motor in gear or out of gear to make lining up the shafts easier. I'll do a search again on that. Any more input is more than welcomely received. UR a DUMARSE, then input, is welcome and expected too. LOL

 

[Chris1956]

Re: Mercury 500 gear engagement

Sounds like the water froze and pushed the bearing cover out. The doughnut shaped retainer is white metal. You can drill a hole in it and crack it out. Gearcases are a bit tricky to rebuild and parts are costly. See if you can pick up a used LU. When you drop the LU, put motor in neutral.

 

[brad1756]

Re: Mercury 500 gear engagement

I know this is a broad question, but what could the damage be, or likely be. I'm assuming that the ice pushed the cover out and likely boogered the threads. If that could be repaired to the point of being able to get another cover to hold, what might else be wrong if anything. Would the cover being shoved out, only, cause the same set of symptoms? Obviously I'm hoping that rethreading and a new cover might fix the problem. Is it possible?

 

[Chris1956]

Re: Mercury 500 gear engagement

Brad, It is not posible to determine (from here) whether the threads can be fixed. You could hold the bearing carrier in the gearcase several other ways however. Three self tapping screws thru the gearcase sides or three pop rivits will hold the bearinf carrier in place.

You need to inspect the gears and bearing to see if any are good.

 

[emckelvy]

Re: Mercury 500 gear engagement

Sounds from the initial description of the damage that the gearcase cover was plastic. If so, that's fortunate 'cause if it was aluminum like the older-style 'nuts', it probably would have held, and the gearcase cracked from ice expansion.

Once you get the propshaft/bearing carrier/reverse gear assy out of the gearcase, check the gearcase internal threads. You may be able to clean them up.

Don't think you can even get an alum carrier nut new from Merc for a 50HP, they're only avail in plastic.

BTW, I bet your driveshaft seals are bad and/or the driveshaft is rusted in the seal area, and this is why you got so much water in the lower unit in the first place.

I'd pull the lower pump body and check seals & driveshaft, in addition to inspecting the propshaft side.

If it's just seals, that's an easy fix. The rusted driveshaft, if it's not too bad, can be repaired by a Redi-Sleeve aka Speedi-Sleeve. Many past threads on that, do a search to find them.

A leaking shift shaft seal can also cause water problems so that's something else to look at while you're in there.

HTH & let us know what you find............ed