Significant rapping of engine then led to grinding/"rock tumbler" sound

[Monarch]

Please help.

I have been using my boat on three different occassions and a rapping sound coming from the motor of my 1996 40 HP Force developed louder and louder each time out and is most significant sounding the more I accelerate. I only went out on average 15 to 20 minutes each of these times. It is a loud rapping that I blamed on exhaust cover contact since my motor has been well maintained and I couldn't see any visual issue present (this goes along with my lack of knowledge of outboards)...

Tonight, I left the dock under slow speed and the engine began to tick as the engine warmed up. After no more than a couple of minutes I calmly accelerated and I began hearing the tick grow louder and then I heard a crackling/grinding sound. This did not sound good at all. I was able to head to shore and I kept things slow. The boat engine does not sputter and it starts first or second turn of key. I began using synthetic engine oil 50:1 ratio.

Any ideas? Your help is greatly appreciated. I am somewhat sick with worry...

Thank you for the responses...

 

[roscoe]

Re: Significant rapping of engine then led to grinding/"rock tumbler" sound

When an engine makes unusual noises, it is talking to you.

I would not run it any more.

Pull the head off and examine.
I don't think you will have to look far to find the problem.

No, your synthetic oil did not cause the damage.

 

[Monarch]

Re: Significant rapping of engine then led to grinding/"rock tumbler" sound

What do you think the issue is? Any ideas? I am not a mechanic and would like to get some feedback on possibilities so I can begin seeking someone who has the technical experience to find and fix my problem.

This is terrible. The motor still drives but what might be the culprit?

 

[john from md]

Re: Significant rapping of engine then led to grinding/"rock tumbler" sound

I could be a piston pin slapping or it could be a main bearing came apart. If you are not mechanically inclined, you need to take it to a mechanic.

John

 

[Monarch]

Re: Significant rapping of engine then led to grinding/"rock tumbler" sound

I started up the motor again today. Under idle it's barely detectable. In reverse, I cannot detect anything abnormal. With a closer listen, it is sound as though the rapping is coming from the midsection of the shaft (near the exhaust port area).

Is it possible if the gear oil is gone/leaked out or water mixed-in with it that that could cause the sound I'm hearing?

It sounds very healthy in reverse... strange. Any ideas? Keep 'em coming please!

Anybody out there from central Maine willing to work on this thing?

Thanks guys!

 

[sailingwest]

Re: Significant rapping of engine then led to grinding/"rock tumbler" sound

HI ,sorry I can not give you any hands on help as I am in Scotland, you say motor sounds fine in reverse so I would suggest you drain the oil out of your lower unit (gearbox) into a plastic container,use a magnet to check if there is any significent amount of metal in the oil,if there is you will have to drop and split the lower unit to find out exactly what is happening ,if the oil is clear of metal refill the unit with fresh oil and tick it off as checked. Jim Byrne

 

[sailingwest]

Re: Significant rapping of engine then led to grinding/"rock tumbler" sound

ps,use new sealing washers on your vent and drain plugs....Jim

 

[sailingwest]

Re: Significant rapping of engine then led to grinding/"rock tumbler" sound

just to be clear a tiny amount of metal in oil is normal ,best of luck.

 

[sailingwest]

Re: Significant rapping of engine then led to grinding/"rock tumbler" sound

HI ,sorry I can not give you any hands on help as I am in Scotland, you say motor sounds fine in reverse so I would suggest you drain the oil out of your lower unit (gearbox) into a plastic container,use a magnet to check if there is any significent amount of metal in the oil,if there is you will have to drop and split the lower unit to find out exactly what is happening ,if the oil is clear of metal refill the unit with fresh oil and tick it off as checked. Jim Byrne

 

[Monarch]

Re: Significant rapping of engine then led to grinding/"rock tumbler" sound

Thank you for the reply, Jim! You are reinforcing my prediction that the gearbox/lower unit is having problems.

Would the shifting be negatively affected by lower unit/gearbox issues I've labelled? It is shifting fine--no problems at all. Spun bearing? Hmmm....

I'm bringing my boat into the marina tomorrow. I hate to do it because the marina can't look at the boat for a week and a half... Do you think the rapping would go away if my issue is depleted gearbox oil and I replaced it with new?

Thanks for your help in advance. Much appreciated!!!! Let me know what you think. I'm hinging upon the idea of NOT bringing the boat in right away.

 

[gonefishin485]

Re: Significant rapping of engine then led to grinding/"rock tumbler" sound

you know, i had an evinrude 35 on my aluminum fishing boat that did something similar, at an idle, ran like a top, perfect in and out the water, reverse was as smooth as glass, forward, it would make a popping noise, was irregular at first, then got more regular with time, could hear a definite popping from the mid section/lower unit area.


long story short, one of the dog gears in the lower unit was slipping and tore up the forward gear. not saying thats YOUR problem, but thats just my experience

my advice, if at all possible, run it in a barrel idling in forward and reverse, you should be able to hear it or maybe even feel it in the center section or lower unit

ohh yeah, and be careful, that evinrude was runnin wide open and locked up up the lower unit on me, slowing me down like i slammed it in reverse and swamped my boat, thank goodness for good bilge pumps!