70 hp. noise

[bigbubba]

I have a 70 2008 that makes a gear clattering noise on deceleration after running at speed....Motor runs fine but started this knocking or clattering noise today and does not do it every time...Oil changed in lower unit every year and only has 220 hours on motor...Changed oil today and no metal or water looks like day i changed it last year...WOT 5600 rpm but I usually go no higher then 5300...Last time it did it today sounded more like a rod knock...Plugs show no sign of not firing properly.....

[Dashunde]

Does it do it only when you pull the throttle back sharply, and never when you decel slowly?
Is it a hollow knocking noise that slows along with the boat then stops before the boat does?

[bigbubba]

Pulling back good n steady ....Sounds like when you kill the motor in gear and the prop still turning....Someone told me maybe a weak dog spring that is putting it in neutral before I put the shift in neutral....

[TownsendsFJR1300]

With the engine in forward and turned OFF, can you rotate the prop? (in either direction).

[bigbubba]

With the engine in forward I can rotate the prop forward and it locks if I try to rotate in reverse....Makes a click or clunk when rotating clockwise or forward ...Did this since was new...I had a 50 yam. did the same thing...

[TownsendsFJR1300]

Have you have the lower unit off recently for any work?

I should clarify, has the LU been off just PRIOR to this issue?

[bigbubba]

No ...I changed the impeller and housing at appx. 150 hours...at least 2 years ago...I fish at least 2 days a week sometimes 4 but I never run more than 4 miles one way....Thats the reason for only 220 hours since 2008....I don't believe in boat riding or should I say I don't care for riding....

[TownsendsFJR1300]

With the engine in forward I can rotate the prop forward and it locks if I try to rotate in reverse....Makes a click or clunk when rotating clockwise or forward ...Did this since was new...I had a 50 yam. did the same thing...

That prop should stay locked and not move (click a tooth by hand) until YOU shift to neutral.

Even if you turned the engine off at WOT, (still in gear), the prop should NOT ROTATE or lower unit make any clicking noise.

Sounds like perhaps shimming or something inside the gear case was either not set up properly from the factory or something is worn.

I asked about previous pulling the LU in case the shifter splines were off a tooth not allowing full engagement.

Wait for someone else to chime in but that's what it sounds like to me...

[bigbubba]

I checked in reverse and it locks so I pulled my shift cable and put the shift lever as far forward as it goes and prop still turns and clicks...I could only move it a 1/16 inch...I guess I will try and drop lower unit and see if I can turn the shift rod a tooth and see...If not I guess to the shop it goes....

[bigbubba]

I pulled up a schematic and from what I can tell there should be no adjustment of the rod in the gear box....The set up on top under the engine is where I would need to move a tooth...?????

[bigbubba]

Well I went through everything on top and all is well...Dropped lower unit and turn shaft to put in reverse...Prop locks up like it should ,,,Put in forward,,,Prop clicks like it shouldn't....I'm thinking it wasn't shimmed rite from the factory and now its got some wear its starting that slip when decelerating...To the shop it goes....Thanks for the responses.....

[TownsendsFJR1300]

Good luck and please post back what they find....

[bigbubba]

Well I took it to the shop today and the mech. told me it was normal for that motor...I guess I just got enough wear in it where it starts doing it when decelerating under certain conditions.....Hope he knows what he's talking about....

[Dashunde]

Well I took it to the shop today and the mech. told me it was normal for that motor...I guess I just got enough wear in it where it starts doing it when decelerating under certain conditions.....Hope he knows what he's talking about....

fwiw I've come across it a few times over the years, in Merc's if I recall, its a fairly distinctive sound.

Its common enough that maybe they're supposed to do it, all brands?
Perhaps its a built-in stability/safety element in case the engine or driveline seizes, stops running suddenly or is ham-fisted while running wide open, in some boats thats well north of 60mph.
I could see a stopped 3-5 blade prop upsetting a fast boat, possibly lifting the rear enough to be...?

Possibly made more pronounced/easily tripped by wear...?

[zenoahphobic]

People might say this is "normal". I would not put up with it if it is so pronounced. It is the prop turning faster than the drive shaft (when decelerating), and it is the dog catching on a gear. Your drive box needs to be examined and setup (shimmed) properly failing that the gear shaft has not been inserted in the right spline location and that the shift cable has not been incorrectly adjusted.