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| Author: | Misterfu02 [ Thu Jul 12, 2018 4:33 pm ] |
| Post subject: | knocking at idle in neutral |
It's only after the boat has been driven for a while. I put it in neutral and it makes a rhythmic knocking sound while idling. If I put it in gear it goes away. Any ideas? I did some research and was told this may be normal. |
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| Author: | Surface Interval [ Thu Jul 12, 2018 8:35 pm ] |
| Post subject: | Re: knocking at idle in neutral |
My '95 190 did that sometimes when warmed up after several seasons of use. I understood that it was gear backlash in the upper end of the outdrive. The engine, drive coupler, and greaseable driveshaft u-joints were good. |
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| Author: | Misterfu02 [ Thu Jul 12, 2018 10:28 pm ] |
| Post subject: | Re: knocking at idle in neutral |
Surface Interval wrote: My '95 190 did that sometimes when warmed up after several seasons of use. I understood that it was gear backlash in the upper end of the outdrive. The engine, drive coupler, and greaseable driveshaft u-joints were good. I remember the 190 my family had as a kid growing up did the same thing! It was also a 95 with the OMC Cobra 5.0 EFI. The way I see it is it's like clutch chatter in a car - some do it more than others. My tow vehicle doesn't do it much, but my Cobalt SS sometimes chatters and makes the same noise in neutral. You can usually get it to go away by pressing in the clutch and letting it out slowly, which would probably be the same as going into gear and back into neutral again, where the noise sometimes goes away. |
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| Author: | Surface Interval [ Sun Jul 15, 2018 10:07 pm ] |
| Post subject: | Re: knocking at idle in neutral |
As the outdrive warms up the oil gets thinner and does not absorb gear backlash as well.. As each of the engine's cylinders fires, the crankshaft accelerates then decelerates. This can cause a slightly irregular rpm in the driveshaft and upper gear set in the outdrive. The engine may not idle at a perfectly stable idle speed because of the size of the flywheel. The driveshaft u-joint is a constant velocity design, but it may not always be a perfectly constant rpm. Because of this, the bevel gear set in the upper end of the outdrive may chatter due to gear lash or clearance btween the driveshaft gear and the forward and reverse gears, I suppose the ideal fix for this is to have the upper half of the outdrive disassembled and re-shimmed to reduce the gear clearance to new specs. The repair shop would love this extra work. This may or may not fix the knock or clatter on neutral. Or you can just run it as is. |
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| Author: | LouC [ Fri Jul 20, 2018 10:50 am ] |
| Post subject: | Re: knocking at idle in neutral |
I've also heard that it helps to use the genuine V/P syn gear oil vs the other generic types. With my 30 year old Cobra, I have never had noise problems. It is totally quiet whether in gear or in neutral. I use the Mercruiser High Performance gear oil at my mechanic's recommendation, have been doing so for over 10 years. |
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