2000 XR6 150hp Noise Like Lower Unit

[hawgcaller]

I'm currently trying to determine a strange noise issue with a 2000 Mercury XR6 150hp V6. Grinding, rapping noise started about two weeks ago when I put the motor in gear, and wound up being that the gears were chewed up. Instead of rebuilding, I decided to just buy an entirely new lower unit complete, so all I had to do was bolt on. Got the new unit, put on the water pump, bolted it on and filled up with gear oil. Took it out three times and got on plane faster than it used to, ran noticeably quiter than before, and lost about 1-2 mph on GPS. The third time out I was coming across the lake at about 58-59mph and lost considerable speed, and once it slowed down the motor cut off/locked. Tried to start it, it would tick like it was in a bind and wouldn't turn over. I trimmed the motor out of the water and turned the prop a few times with my net, turned the ignition and it fired up. It started making the same tap/rap noise it did before on the original lower unit when the gears were ruined. The raps/taps increase with acceleration, reverse is more prominent and sounds like it doesn't like being in gear (just like before). I sent the lower unit back to manufacturer and they put on another motor and said it was absolutely fine, and that I have problems elsewhere. What else on my motor could be making that same sound? Warped head?

 

[Chris1956]

Re: 2000 XR6 150hp Noise Like Lower Unit

What do the spark plugs look like? Take a compression test.

 

[hawgcaller]

Re: 2000 XR6 150hp Noise Like Lower Unit

Got my answer. Compression was 135psi on 5 of the cylinders and 35psi on one of the cylinders. New motor time probably.

 

[mxzer29]

Re: 2000 XR6 150hp Noise Like Lower Unit

You should be able to just that cylinder...I lost the centercylinder of my 94 marniner Mag 150 2.5 liter last summer..my mechanic honed lightly and put a new piston rings in that cylinder...THe cause was oil injection stoped working..Cost me 600 bucks and he put two new thermastats.
Let me know how you made out
tks

 

[Chris1956]

Re: 2000 XR6 150hp Noise Like Lower Unit

mxzer, an oil injection failure will take out all cylinders. I recommend you clean the middle carb on your motor as it likely ran lean.
Hawg, Normally you will need to get the bad cylinder bored out and replace the piston with a new oversize piston and rings. Honing will only work if the damage is really slight, which is very unusual.