Almost ran aground, slight knocking noise now

[robrike]

Hi,
Was out boating on my Dad's boat last weekend and running about 12 or 13mph and missed a marker and got into some muddy silt bottom. Hull never made contact but drive did. Has a 2008 Volvo Penta 5.7Gxi-J with a DPS-A outdrive with stainless props. Rear prop had tiny knick that was hard to even see. The skeg had the paint abraded off pretty good but no damage aside from that. I took it to the dock and went under it with a mask the next morning looking for signs of prop oil seal leaking. Nothing visible and no sheen on surface of water. Went for test run and after light loads got it up to almost 50mph at 5000rpm and was smooth as could be. Now for the kicker,,,

Get a call from my Dad today and he says there is a knocking sound from drive when in gear at idle, could not tell at speed due to engine noise. At the dock in neutral he says he and a boat dealer guy could hear it even though drive was not in gear. Boat guy said to not run it anymore till it was checked by a mechanic. I made sure props were straight and there was no signs of damage when I was there. I live 200 miles away so hoping to get some insight on what a mechanic should check so I can make sure guy is honest with my Dad. When the drive ran into bottom I tilted it up, shut off engine and brought drive to top. I backed out with drive tilted to upper run range and backed out at idle till I was in deeper water.

I am a pretty good shade tree mechanic and knew what to check at the time while it was in the water. The engine never ran hot so any silt pulled in went right out and did not damage impeller though I plan to replace it next trip down. Does the U-joint assembly turn with engine in idle and shifter in neutral? I have the shop manual on pdf but could not find info in there. We have had engine and stern oil changed each spring since it was purchased. When I ran it the day after our incident everything was fine and I have a spidey sense that notices any odd vibrations or sounds well before the normal human ear or sense of feel does. There were none.

Any thoughts on what to expect mechanic to check and what typically incurs damaged in this type of situation?

Sorry for the novel.

Thanks for any insight. Being 200 miles away leaves me to "armchair quarterback" the situation. Might be able to take a day off and go down and access things more.

Thanks,
Rob

 

[saintlee]

Re: Almost ran aground, slight knocking noise now

Does the U-joint assembly turn with engine in idle and shifter in neutral
yes the u-joint assembly turns with the engine
regardless of in or out of gear.
if u ran engine with outdrive all the way up, at all, could be u-joints or gimbal bearing

 

[robrike]

Re: Almost ran aground, slight knocking noise now

Hey saintlee,
Thanks for the reply. I did not run it with drive all the way up to trailer position. I only put it in gear with no throttle above idle but it could have been too high. Manual said it could be run with drive tilted 6 to 29 degrees and below 1000rpm. That would make sense though that u-joint could be culprit if it turns even in neutral since they heard it in neutral at dock. I am getting ready to read up on u-joint and gimbal bearing replacement in the shop manual. Try to get an idea of $$$$'s for worst case scenario.
Thanks again,
Rob

 

[robrike]

Re: Almost ran aground, slight knocking noise now

I am very pleased to report that we had a boat mechanic come out and listen to the drive and check the drive for water in the gear oil and all checked out fine. The noise is only in neutral and goes away once in gear. He said that what was heard was the gear lash in the upper part of the drive. I do recall seeing a post here about that on a DP-S and everything else checked good. Thanks for the information though, 120 hours on the boat and he said it is not uncommon.
Big relief for me.
Thanks,
Rob