Is knocking do to prop???

[meanmom]

73 115hp Johnson OB all 4 pistons have 118to123 compressions lower unit has no metal on magnets. Sound is only there when boat is in water and in forwarder or rev I believe I spun out my prop could this be the knock. Motor has the same pick up and run just like it did before the knocking sounds started thank for the help

 

[Daviet]

Re: Is knocking do to prop???

If the engine preforms the same you most likely did not spin the prop.
Have you checked the lower unit oil , is there any water or metal particles in it?

 

[meanmom]

Re: Is knocking do to prop???

yes there is metal particles in the oil but not on magnet but no water

 

[Cofe]

Re: Is knocking do to prop???

Aluminum or some stainless steels are not magnetic.

 

[meanmom]

Re: Is knocking do to prop???

what is EH10 gas can i have a attwood 6 gl

 

[ondarvr]

Re: Is knocking do to prop???

We need more information on the "knock", is it a deep thump or more of a ticking sound? is it 100% of the time, does it change directly with RPM?

 

[Al-53]

Re: Is knocking do to prop???

what is EH10 gas can i have a attwood 6 gl

he means the E10 gas can cause problems is all

Al

 

[jtexas]

Re: Is knocking do to prop???

Gearbox making metal, is not good news.

Any damage on the prop? It's not hitting the trim tab, is it?

If you're sure that sound is coming from the lower unit, it'll have to be disassembled for inspection.

10% ethanol-blended gasoline. Nothing to do with the lower unit. Any modern plastic (polypropylene) tank will do fine.

 

[bob johnson]

Re: Is knocking do to prop???

if you rev the motor slightly in nuetral maybe to 2000 or 2500 rpms for a split second...can you still hear the knocking???

if so

then it isnt in the LU!!

if thats the case and you DONT hear it in nuetral. id discconnect the shift linkage and shift the motor BY hand on the motor, and make sure you got the full stroke.....

do you still hear the knocking??


bob

 

[meanmom]

Re: Is knocking do to prop???

Any damage on the prop? yes just some small chips It's not hitting the trim tab, is it? no

If you're sure that sound is coming from the lower unit. no but it sounds like it coming from the bottom of the motor.

i took the LU off and all look good but iam anewbe

We need more information on the "knock", is it a deep thump yes it is

if you rev the motor slightly in nuetral maybe to 2000 or 2500 rpms for a split second...can you still hear the knocking??? I will try this when get it back to the lake.
if you still need more info please ask me and thanks for the help

 

[jtexas]

Re: Is knocking do to prop???

be advised that the pinion gear is meshed with the drive gears 100% of the time; the drive gears are spinning even when the motor's in neutral, freewheeling on the prop shaft.

So, knocking in neutral does not rule out the gearbox as the source of the sound.

When you put the motor in gear, the clutch dog engages one of the drive gears -- the clutch dog is splined to the propshaft which makes the prop spin.

Read this thread before revving your motor in neutral, even for a second:
http://forums.iboats.com/showthread.php?t=430070

 

[bob johnson]

Re: Is knocking do to prop???

be advised that the pinion gear is meshed with the drive gears 100% of the time; the drive gears are spinning even when the motor's in neutral, freewheeling on the prop shaft.

So, knocking in neutral does not rule out the gearbox as the source of the sound.

When you put the motor in gear, the clutch dog engages one of the drive gears -- the clutch dog is splined to the propshaft which makes the prop spin.

Read this thread before revving your motor in neutral, even for a second:
http://forums.iboats.com/showthread.php?t=430070

I mentioned that to try and isolate the clutch dog...

more common of a LU knocking than a missing pinion tooth or other pinion noise..I would think...

but I guess one of the shafts Drive or prop could be seriously bent and the pinion and gears could be binding....or something could be jammed in bwteen a few teeth of a gear!!


bob

 

[meanmom]

Re: Is knocking do to prop???

So i just need to open up the LU and look is ther away to tell if the shafts are bad without opening the gear box and if not how hard of a job is it

 

[jtexas]

Re: Is knocking do to prop???

It's not something to attempt without a factory shop manual in hand.

 

[meanmom]

Re: Is knocking do to prop???

I have the johnson outboard shop manual on disc and pretty with my hands i just never worked on boat motors

 

[bob johnson]

Re: Is knocking do to prop???

So i just need to open up the LU and look is ther away to tell if the shafts are bad without opening the gear box and if not how hard of a job is it

there is no gear box..

you dont really "open" the lower unit...you take it apart!!!! piece by piece...and sometimes there are special tools and sometimes there are tough assemblies to undo.....via corrosion or damage...

Id do all you can to prove the power head isnt the issue before you try to take the LU apart.

bob