Clunking noise on 50 HP Yamaha 2 stroke - gear case oil?

[seasponge]

We have an early model Yamaha 2 stroke 50HP motor (50DETO 6H5).

On the weekend, we removed the lower unit to flush out the water cooling system. No problems there. After we put it back together and got it in the water, we had problems getting it into reverse gear. Took it out of the water. After a search of the internet for solutions, we then put the throttle in reverse (it did not engage), disconnected the shift rod (not sure of the correct term), pushed the lower part of the shift rod down whilst turning the prop until it engaged into reverse gear, then reconnected the shift rod with the barrel nut and locking nut. Checked it with the muffs on, then put it in the water. The problem seemed to be solved, we can now engage reverse, it sits nicely in neutral, and engages forwards ok.

The problem now is that whilst in forward, the motor will now make quite a heavy clunk/knock/shudder. It doesn't happens whilst engaging, it happens after that as we throttle up. As we start to increase speed, we might get one clunk, then its ok, and as we get towards full throttle, the knocks happen continuously till we back it off.

Anyone have any suggestions as to a possible cause? I'm not sure whether its related to what we did when taking the lower unit off and fixing the shift rod, or whether its just coincidence.

Is it just that the gear case needs new/more oil (haven't checked the oil status yet). What symptoms would we see if the gear case was low on oil?

[Fab1]

Maybe i,m wrong but I'd be double checking the linkages are adjusted correctly,sounds like you have the adjustment set to much to reverse than forward.

Sounds like when slipping her into fwd the gears aren't fully meshed causing the noise.

For future reference when disconnecting the shift rod locknut and unscrewing mark with paint or count the threads/turns.

Cheers.

[tryhard]

Think Fab1 is right.

Sounds like the Dog clutch(if that's the correct term)

Needs some adjustment - Check with Craig or Roger at Huetts.

[seasponge]

Is there much adjustment within that shift rod assembly? I thought it was either engaged or not. There is no problem engaging, the noise occurs after forward is engaged and we are already moving, and then again nearing full throttle. When the noise happens, it doesn't seem like its slipping out of gear, there is no excess revving or loss of speed, just a large clunk then keeps going. I've been trying to find a lower unit assembly drawing for that model but can't find one.

[a boat]

Sounds like it is jumping out of gear because the clutch dog is not fully engaging the gear. If it did not do it before you remove the gearbox then as the guys have said you need to adjust the relationship between the top and bottom shift shaft. Big damage to the gears and clutch dog can happen each time it jumps out of gear so it was to be fix ASAP.

[seasponge]

Thanks for the reply Craig.

This is the lower unit assembly drawing for my model (1984 50ETLN) http://www.boats.net/parts/search/Yamaha/Outboard/1984/50ETSN/LOWER%20DRIVE%201/parts.html

My understanding, to connect the linkage correctly, is to,

1. With engine in neutral, undo barrel nut and lock nut
2. Break shift rod connection
3. Whilst rotating prop in reverse, push lower shift rod down to engage reverse gear in the gear case (done in reverse gear to give better access to barrel nut)
4. Put remote control lever into reverse
5. Connect shift rods with barrel nut with 5-6 threads onto the lower shift rod
6. Tighten lock nut.

Have I missed anything, and where, if any, is there room for minor adjustments?

thanks.

Edited January 9, 2015 by seasponge