300hp 4.2l v6 gearbox noise

[Jordanhack]

Evening all,

I have twin 300hp 4.2l 2013 models with dts. One of the lower units has noise when I spin the prop by hand. Sort of like a the gears aren't quite meshing properly. Not crunching or grinding. The other motor is quiet as a mouse when I spin the prop. Drop leg oil. Oil is clean and very very minimal metal shavings on the magnet plug. Refilled and noise still there. No play in anything and spins very freely. Even more freely than the quiet one. Should I be looking at a potential rebuild? Is there a possibility the digital throttle shift is not 100% in neutral? All help greatly appreciated

[99yam40]

are these F 300s?
is one a LF
complete model #s help

Is there a way to disconnect the shifter so you can try moving it to neutral by hand?

[Jordanhack]

So both engines are FL300BET ultra long leg which I see now are both counter rotating models. However the gearbox on the engine with the noise is standard rotation(starboard side). Bit confused as to why this is so but I bought the motors second hand with 1200ish hours on them and just realise this now. Havent had a chance to see if I can disconnect the shifter at all but will have a look this afternoon.

[zenoahphobic]

It's misleading when the term counter rotating is used. The engines above rotate in the same direction, and so does the lower unit. What rotation change is that the counter rotating engine has reverse engaged for forward and uses a lefthanded prop.
The clicking is common, and usually, as you have guessed, can be adjusted out at neutral

[Jordanhack]

So I manually put it in and out of gear. No difference. Still quite a loud whirring gear noise...certainly not a clicking noise I don't think. I can hear a click when I rock the prop on the other motor back and forth. Starting to think a gearbox on its way out

[99yam40]

all you can do is open it up and see what you have going on.

has this noise just started?

[DennisG01]

I'm not real familiar with your setup, but in regards to Mercruisers, the shift cable can sometimes stretch. Even with DTS (again, with Mercruisers) there is a still a shift cable form the DTS shifting module to the drive). When that does, neutral really isn't "neutral" anymore - it ends being being biased one way or the other (slightly forward or slightly reverse). Not engaged, but enough that the gears touch slightly (giving off a light clicking sound). In the early stages of cable stretch, it can often be adjusted. Eventually, the cable would need replacing.

Just to repeat - this is the case with Mercruisers - I'm not sure if your setup uses an adjustable cable or rod - but if it does, that "could" be the issue.

You said "manually"... does that mean you disconnected the shift control mechanism from the shifter rod (or whatever the mechanical thing is in your engine that goes down to the foot). If so, you eliminated what I was talking about as a variable!

[zenoahphobic]

So I manually put it in and out of gear. No difference. Still quite a loud whirring gear noise...certainly not a clicking noise I don't think. I can hear a click when I rock the prop on the other motor back and forth. Starting to think a gearbox on its way out

How fast are you spinning that prop? Very fast a clicking could possibly turn into a whir (be careful with your hands when “spinning”).

If the whirring is still evident when turning the prop slowly, it would not be the gears and more likely:
1 something in the hub has broken or changed position; or 2. a bearig(s) is failing; or 3. Possibly something like fishing wire has found itself under the seal and or contacting the bearing.
Be cautious in accepting that the oil is clean means no serious damage inside. It could have been changed and flushed prior to your purchase (you haven’t run that engine).
I would take off the prop and have a good look at that seal and bearing behind.
If all still appears good I would run the engine (with Muff or water supply) and see if you can detect that whir in gear, before embarking on a complete tear down.

[pstephens46]

How fast are you spinning that prop? Very fast a clicking could possibly turn into a whir (be careful with your hands when “spinning”).

If the whirring is still evident when turning the prop slowly, it would not be the gears and more likely:
1 something in the hub has broken or changed position; or 2. a bearig(s) is failing; or 3. Possibly something like fishing wire has found itself under the seal and or contacting the bearing.
Be cautious in accepting that the oil is clean means no serious damage inside. It could have been changed and flushed prior to your purchase (you haven’t run that engine).
I would take off the prop and have a good look at that seal and bearing behind.
If all still appears good I would run the engine (with Muff or water supply) and see if you can detect that whir in gear, before embarking on a complete tear down.

I’d keep running and see if it gets worse. At least he will not get stranded with two motors. Why spend the big money until you are 100% sure? Where is Rodbolt?

Zeno - what’s the latest on the fires down there?

[pstephens46]

replied - flagged for inspection

Slow enough around here without this crap