Johnson 115hp Rebuild Knocking

[asignabove]

I have recently had a 2001 Johnson 115hp powerhead rebuilt and only has about 1.5 hours on it. The question is that when the throttle is reduced(decelerated) the engine knocks loudly. The rebuilder says that the rumble is normal, but it does not sound like a rumble or a pinging it sounds like a rod knocking. I had it checked by a mechanic and he could not find anything wrong. The timing is set and there is no play in the pistons and the compression for all cylinders is around 147. He doesn't think that the sound is normal but he can't find anything wrong. He was the one that was told that rumble sound is normal by the company that rebuilt the powerhead. He checked the lower unit and it is fine as well. We are at a loss on what to check next if anything. The knocking progressivly get louder as it warms up. Any suggestions would be greatly appreciated.

 

[rabidfish]

Re: Johnson 115hp Rebuild Knocking

Sometimes, the boring bar doesn't get "all the way" to the bottom of a bore. The slight "step" that's left can hit the piston skirt. Try this, remove the spark plugs and turn the flywheel by hand. Do you feel any "tight" spots?

 

[R.Johnson]

Re: Johnson 115hp Rebuild Knocking

When you decelerate, hit the primer and see if it goes away. You have a deceleration knock.

 

[Jcrain]

Re: Johnson 115hp Rebuild Knocking

RJohnson: Can you describe a "Deceleration knock"?

 

[Dhadley]

Re: Johnson 115hp Rebuild Knocking

On 60 degree motors there is a situation known as "de-cell knock" as RJ refers to. It has to do with the motors running lean on quick decelleration for a short period of time. As he mentions hit the primer the next time, it should go away. It doesnt hurt anything and not all motors do it. Backpressure seems to have a lot to do with it. <br /><br />We've worked with motors that had a history of it and found no damage to the powerhead because of the motor doing it.

 

[asignabove]

Re: Johnson 115hp Rebuild Knocking

This is the second rebuilt powerhead on this motor. The first rebuilt powerhead had this same sound as well and after about 15 hours of running it, it blew the #1 cylinder piston rings. Sent it back to the company and they either just fixed the one cylinder or provided another rebuilt powerhead(not sure, more than likley just rebuilt the one cylinder). Was never told whether the sound had anything to do with the rings going bad. On the first powerhead before it blew, I tried the primer and it did not help with the sound. I am a little leary of running this one until I am confident that the sound is just a normal sound by either a de-cell knock or something that comes with a rebuild. Is there a way to either quite the de-cell knock down or to eliminate it? That way I can rule out any machanical problems before it leaves me stranded again.

 

[asignabove]

Re: Johnson 115hp Rebuild Knocking

I have read that changing to mid-range jets to enrichen the fuel would help. Has anyone had any success with this?

 

[angus63]

Re: Johnson 115hp Rebuild Knocking

Like posted by Dhadley, bump the key in during quick decelleration and see if the knocking stops.<br />If you do not hear a "knocking" thru the entire RPM range or when you slow down gently, I'd bet on the decel knock (my 95 175hp 60° V6 Oceanpro has the same ping you describe). Yes, richening the midrange "helps", but often doesn't eliminate the ping. I slow down gently and haven't noticed it for years and have not suffered any damage as a result. <br />Good luck<br />PS I expect you have a warranty on the rebuild. Bring the Tech with you for a ride and let him hear it and document what he says to cover your fears.

 

[jgrisham02633]

Re: Johnson 115hp Rebuild Knocking

Just a long shot but, I have a '95 60o 115 and it also made a noise similar to a knock but it was just noise coming from the leg traveling up to the powerhead from a misadjusted shifter, probably not your problem but worth checking out?