gt40 knocking

[east tx skier]

I suspect this is not the case, but it never hurts to mention it. Is the boat in gear when you hear this noise? Reverse possibly?

I had the strangest rattle in reverse on my old boat. Never heard it in forward gear.

Finally, it dawned on me. My ny-lock prop nut had worked its way loose. In reverse, the force of the water was pushing the prop down the tapered shaft and causing it to wobble. In forward gear, the responsive force of the water would snug the prop back up. It wasn't terribly lose. But just lose enough to knock around in reverse.

Since you mention revving it, I figure this is not your problem, but the last time I brought this us, I was on the money. So I figure it can't hurt to repeat this story.

[93nautique0710]

run some seafoam through the throttle plate or a vaccum line to clean the top end.

it could be a piece of carbon that got broke of by fogging oil over the winterization so many things it could be

[steve-o]

Sounds too deep. This sounds like something coming from the lower end. Real deep, like spun bearing or something. Hope it's not. Might be harmonic balancer, which would be much cheaper. Really sounds like a bearing though. Did it get run low of oil? That sounds like a rod with slack in it.

[east tx skier]

Disregard my last post. I just listened to the .wmv file.

[g33b0]

im not sure if engine was ever overheated..................bought boat two years ago, and only took it out twice last year.........and def didnt hear the knock..............oil was changed when i bought it .........str 40wt..........and i changed oil a week ago 40w....and then changed oil again this morning to 20w50 vr1........... about to pull valve cover and take a look..........what exactly would be a tell tell sign on the up end.......rocker arm pushrods, what am i going to be looking for

[93nautique0710]

Sounds too deep. This sounds like something coming from the lower end. Real deep, like spun bearing or something. Hope it's not. Might be harmonic balancer, which would be much cheaper. Really sounds like a bearing though. Did it get run low of oil? That sounds like a rod with slack in it.

it does sound like a rod bearing but i didnt want to tell him he needs a engine without checking all the other cheaper possiblities i would take it to a pro before throwing a engine in it

[93nautique0710]

im not sure if engine was ever overheated..................bought boat two years ago, and only took it out twice last year.........and def didnt hear the knock..............oil was changed when i bought it .........str 40wt..........and i changed oil a week ago 40w....and then changed oil again this morning to 20w50 vr1........... about to pull valve cover and take a look..........what exactly would be a tell tell sign on the up end.......rocker arm pushrods, what am i going to be looking for

if your going to check the rockers when u pull the valve covers roll engine over to the valves your going to check is fully closed and the pushrods sould have no lash in them up and down movment and just check and see if all the rocker bolts are tight

[g33b0]

new engine.........

[g33b0]

pulled one valve cover side off and all seemed to be tight...........pushrods were not visially bent from the top that i could see............what exactly is the piece ontop of the engine........fuel injection i think...............i know that knocks will resonate throughout....but it seems that the knocking is coming from the aluminum looking tank ontop of the engine

[steve-o]

Are you talking about the intake?

Unfortunately I think you need to take it to a mechanic. The sound in that file does not sound like anything in the top end. It sounds like a spun rod bearing, which in some cases is not as bad as it sounds. Definitely do not run the engine anymore. You run the risk of causing damage to the crankshaft and other parts on the bottom end. A spun rod bearing is going to make noise from the engine push rods. It may sound like it is coming from under the intake as that entire assembly is wobbling around on the crankshaft. I have heard a harmonic balancer that was cracked make a similar noise before, too. The reason I asked about the oil changes and overheating is because what usually causes a spun rod bearing is lack of oil, dirty oil and overheating or all.

And again, it might not be anything major, but it looks like a mechanic that you can take the boat to and let him diagnose it is going to be the best course of action. You might get lucky and find a member that would be willing to help out that lives closer and knows engines.

[g33b0]

mechanic

well i dont want to jack anything up more than it might be already.......i found a mechanic in midland tx that says he can take a look at it..........not the first place i would choose, i would prefer a nautique certified shop but the closest is about 500 miles away......price you pay for living in west texas....... dangit, i hate paying people to do what i wish i could do myself........i am just gonna have him diagnose the problem and put his 2cents in and then decide if i will have him do the work or myself................now here is a question..............out of the list of things that could be wrong.......what is the most expensive to replace and hardest to get to...and which should i let a mechanic do or do myself...... from the look of it, pushrods and lifters seem to be a simple fix..........................fyi, i took the valve cover off, put manifold and riser back on and ran engine, valves all seemed to be doin fine, that is when i heard the knocking from that piece directly ontop of the engine that the flame arrestor is connected too, guessing the intake?.......

[steve-o]

Are you getting any water in the bilge with the boat running?

[g33b0]

i was getting water in the bilge from a cracked muffler......i fiberglassed and repaired the muffler and then coated it with a rubber coating for shock absorbtion.......and no more water.....i have looked up and down the block for leaks and dripping and all "seem" to be good.............thinking i will need manifold and riser gaskets now,...these looked pretty rough...........i replaced the tranny oil cooler earlier this year also......

[steve-o]

I was going to say after listening to the wmv again, it kind of also sounds like a muffler that is split in half. It would be spewing water though.

If you search youtube for spun rod bearing you will be able to listen to hundreds of videos of how it sounds and compare to what you are hearing. That deep knock is a giveaway.

Check all your pulleys and make sure they aren't moving/rocking (the video just sounds so much louder than that) and then let him look at it.

[Nautiquehunter]

This is very hard to tell without being there . If the oil pressure is good its not a bearing. It sounds Like a lifter to me? This problem occurred after sitting over the winter? Its more likely that a lifter has bled down and now it cant pump back up than spinning a bearing by just sitting. It will be interesting to see what the mechanic says.