Merc 500 grinding sound post LU rebuild

[afmackinnon]

I'm getting discouraged I have a 69 merc 500 that runs great but had a bad prop shaft seal so I pulled the carrier and put a new seal in it reassembled and reinstalled. Plunked the boat in the water and as soon as I open up the throttle even slightly I hear a nasty grinding sound. Smooth and consistent grind that goes away as soon as I let off. I can have it in gear and putter along free of the grinding but as soon as I try and give it some gas the grinding comes back. I found oil coming from the two rectangular slots at the top of the midsection. A nasty brown colour and the lower unit oil is cloudy yellow. I pulled the carrier again and the teeth look good no damage done but I noticed some blue colouring almost like ink on some of the teeth that I don't recall seeing. I'm a mechanically inclined newbie who's completely lost on this one. Please help!

 

[CharlieB]

Re: Merc 500 grinding sound post LU rebuild

If you still have it apart, check the square edges of the shifter slider, the engagement 'dogs'. This is the parts that engage when shifted into the gear. If the shift shaft is index incorrectly, like one spline off, they do not engage all the way and can rapidly 'bounce' as they slip and bag into each other.

Once reassembled check to make sure the gearcase shifts fully into each position F - N - R. While in gear step on the prop and see if you can turn the motor with your weight on the prop. Repeat in both F and R. In F you will have to turn the prop CCW or the clutch will ratchet. Normally if they lock well enough to hold your weight turning the motor it should hold fine running.

 

[carholme]

Re: Merc 500 grinding sound post LU rebuild

The blue colouring on the gear teeth is probably machinists dye that is used to read the gear pattern after shimming is done. Grinding when you add throttle and decreasing when you reduce throttle sounds like the bearing carrier may not have been all the way in. Do you recall the torque you applied to the cover nut?

The other important thing of course is if you lost a shim/s from the stackup as it is these shims which set the correct gear mating.

Gerry