Gear Jumping?

[nrowles]

Hello all. I have a 1964 Merc 60 6 hp. When pushing my boat into the river last weekend my prop hit a rock making what sounded like a "metal popping" noise. When I starting motoring it seemed to be gear jumping at higher rpm. My first thought was prop hub. I still need to put back in water to test that to rule out. The reason I think it may be something else is becasue of the noise it made. I read it could also be the clutch dog and/or gears. If assuming the noise it made is what caused the problem, I wouldn't think the clutch dog or gears would instantly be going bad. Is there anything else in addition to these items (prop hub, clutch dog, gears) that would cause the motor to be gear jumping? Specifically after making a noise when bumping the prop into a rock going backwards? Shift adjuster, linkages, timings, etc.? Thanks and sorry for the long post, I just wanted to give all details.

 

[Texasmark]

Re: Gear Jumping?

If the little guys are like their big brothers R gear is connected via square "pins and sockets" if you will. There are at least 3 of them on the older engines and 6 on today's engines. I can only assume that they upped the number to make the R shifter more durable, possibly for reasons such as yours. It's because they are square, that when putting the engine in R, if not running, you need to rotate the prop by hand while putting light pressure on the shifter until these line up and engage, then the shifter will go all the way into position. With the engine running, the pins on the clutch dog are spinning and find their R gear mates on their own.

Hitting something in R puts tremendous strain on your clamp brackets, engine swivel mechanism, and transom. I doubt any of your shifting linkage has a clue that it happened.....no interconnect mechanism vulnerable to the attack other than stripping out your engagement mechanism mentioned above!

F gear has nothing really in common with R gear from the clutch dog/lower unit aspect. The R connection on the dog is off the rear and engages the R drive. The F is off the front end of the dog and engages the F gear off the front of the dog. So if you are running in F and hear funny noises, either it is something else, or you broke off some alum from the rear of your dog and it is floating around in your LU. Draining your oil and looking for metal pieces/shavings could answer that question...you would be looking for significant alum not just miniscule shaving here and there cause there always be "some".....use new gaskets when you put the screws back in.

I would assume that your prop has a rubber hub which is designed to slip and reengage when hitting and clearing an obstacle. If you really whacked the rock, and it didn't break loose as designed, then you MIGHT have clutch dog-R gear interface problems. But, I'd check the oil as stated, pull the prop and mark it from the bronze hub straight out to the outer edge of the hub with a magic marker and a straight line. Go and run it and take the prop back off. If the lines are no longer in alignment, get a new prop or have this one fixed.

HTH,

Mark

 

[nrowles]

Re: Gear Jumping?

Thank you for the detailed response. The boat motor was actually not even running when this happened and it should have been in neutral. We were pushing the boat (rear first) into the water from the banks when we hit the rock straight on. Also I have not noticed any noises while motoring, just "gear jumping". The noise was when we hit the rock pushing in and it did not sound like normal metal to rock noise. Do you think your response still applies given these details?

Here is a link to the schematic. Next to last page.

http://johnsoldmercurysite.com/whitepapers/manuals/MERC 60.pdf

 

[Texasmark]

Re: Gear Jumping?

Thank you for the detailed response. The boat motor was actually not even running when this happened and it should have been in neutral. We were pushing the boat (rear first) into the water from the banks when we hit the rock straight on. Also I have not noticed any noises while motoring, just "gear jumping". The noise was when we hit the rock pushing in and it did not sound like normal metal to rock noise. Do you think your response still applies given these details?

Here is a link to the schematic. Next to last page.

http://johnsoldmercurysite.com/whitepapers/manuals/MERC 60.pdf

I pulled the schematic and see that in 40+ years they still do things the same....pretty much, they cleaned up the rear cover because when you operated in salt water and had to take that spanner nut off to pull the bearing carrier, the threads were so corroded you could hardly get at it. BTDT

You didn't tell me which gear you are in when you get the gear hopping and exactly what you are referring to. In looking at the schematic, reverse pressure on the prop shaft would attempt to push the prop shaft 45 into the front roller shaft bearing 41 and cram it into the F gear 40 which could force it into the F gear bearing 39. If it could, and I would think not, as when you install these components you install them all the way in the housings...drive them in till they stop moving, it would tend to allow the prop shaft to move forward a few thousands. This would help your F gear stay locked in but, especially in an engine of that vintage, could slightly unseat the clutch dog from the R gear since the dog couldn't move aft as far as it had been moving, allowing for it to slip off a rounded gear edge (wear item). Since the whole shift mechanism is spring loaded, the high thrust that the higher rpms put on the interface could force it out of it's socket and allow it to skip giving you a lock/break/lock/break kind of performance. But again, this would be in R only and one wouldn't think that you back up all that fast anyway.....water over the transom!

Before I tore into this I would go to a prop shop and tell them what's going on and have them check your rubber hub. Proper functioning of the hub is to slip when you hit an object and reseat.....time lapse and rpm required to reseat depend upon how good your hub locks to your prop shell. So if you damaged it, it could easily slip lock, slip lock, slip lock.....this action could transfer unusual vibrations to the engine and cause funny noises/clunking, etc. The hub cushioned the impact that was transferred to the propshaft/gearbox and as stout as that assembly is, I just can't see you all of a sudden having a slip problem with the dog.

Keep us in the loop on this as it is very interesting.

Mark

 

[nrowles]

Re: Gear Jumping?

I put the boat in the water over the weekend after having the prop off and putting it back on and the motor did not gear jump once. I have no idea what was going on. Is it possible that if the prop nut was very slightly loose it would act as though it was gear jumping? The spline spacer is slightly rounded on the inner edge as though it was not fully on the prop shaft. Also, when I did get back this weekend I checked for prop nut tightness and I did get a slight turn on it. If this could have possible been my problem and hitting the rock making an odd noise was just a coincidence, what can I do to keep the prop nut tight? Should I get a nylon lock nut?

 

[mfre111]

Re: Gear Jumping?

Hi. The first thing I would check is that the propeller shaft is not bent. If it is, (those square pins that were talked about earlier are called dogs) when you put pressure on the engine, meaning when it is in the water and in gear with the propeller on it. What can happen is that the dogs will slip past each other making it jump. Just like it is going in and out of gear. Don't run it too much doing this. It will round the edges of the dogs. Then you will have to replace the gears and slider that makes it go from forward to reverse. If the shaft does not appear to be bent, then either the dogs are rounded off or you bent something. In either case you will have to pull the lower unit apart to find out. Good luck!

 

[mfre111]

Re: Gear Jumping?

In the schematic for the lower unit from the link above. The numbers that you are concerned with are.
The shaft #45
The slider #43
The forward gear #40
The reverse gear #46
I would check it all out since you will have it apart. Make sure that the carrier #56 is not broken or the case as well.
as I said check it all out. Good luck once again.