unknown Knocking on mercruiser 3.0

[brandenclouse]

I have just bought a boat with a mercruiser 3.0 140hp the guys said he just had it overhauld.. he started it for me when i was there and it was quiet as can be . took it out on the lake when we got it home ,and within leaving 10 min from the dock the motor starts to ping at 3/4 // full throttle. I got nervouse with this being my first boat owned and idled it back to dock to trailer it .. It is now for sure a knock not a ping, but i cant tell where it is comming from. What do I need to check or do .. any ideas would be appriciated concidering this is my first buy in the boating world ..Thanks

 

[Alpheus]

Re: unknown Knocking on mercruiser 3.0

How many hours on it since overhaul?

Did you check the oil before you left?

Have you checked the oil when you came back?

Any proof engine was overhauled?

Did you ever notice if oil pressure was low?

check your oil. If its clean and at the correct level, put the muffs on your boat and start the engine. Pull a spark plug wire off one at a time and listen if the knock goes away...

 

[brandenclouse]

Re: unknown Knocking on mercruiser 3.0

Yes it was just change during the overhaul.. I checked before putting in on the lake and was good color looking new and full.. also checked when on the trailer and the same. had some friends come over with a little more knowledge than me .. and we pulled the spark plugs one at a time ,the only thing that made a difference was cylinder 1 when pulled the plug it wasnt as loud as before and seem to slow down a little but could still here it.. all the rest made no difference at all.. hes said the boat had only about 4 hours on it since the overhaul. oil pressure was 40 when on the water. as far as proof i called the guy and said that he was going to contact his gm guy..and call me back but you know how that goes, no returned call ... yet.. it deffinatly is a loud knock from what the guys here could tell me.. thanks for helping like i said im new at this..

 

[brandenclouse]

Re: unknown Knocking on mercruiser 3.0

This also may be a dumb? but how do you determine weather the sound is from to topend or the lower unit ... this is what people ask me when i tell them... they want to know where the noise is comming from top or bottom and i dont know what to tell them
.. thanks

 

[Bifflefan]

Re: unknown Knocking on mercruiser 3.0

the only thing that made a difference was cylinder 1 when pulled the plug it wasnt as loud as before and seem to slow down.

That sounds like a wrist pin problem.
Does it go away when the engine is cold and then return when warmed up?
The oil pressure is good, as long its was not 80 psi before and dropped to 40 psi when the knocking started.

they want to know where the noise is comming from top or bottom and i dont know what to tell them

This kind of comes with experence.
But, a clicking noise is rockers, a lower pitched knock is rods, an even lower pitched knock under a load is mains. A simular knock to a rod is a wrist pin, but can go away when that cylinder is not under a load.
This is not an absolute by any means and the same sounds can be different to other people.

he started it for me when i was there and it was quiet as can be . took it out on the lake when we got it home

Always take it for a test ride.

 

[brandenclouse]

Re: unknown Knocking on mercruiser 3.0

The knock does not go away when warmed up...or cooled down ..even at an idle its a loud knock. oil pressure was 40 all the time. doesent seem to matter weather it has a load or not.. thanks for the advise on test driving ... like i said this is my first boat and I deffiantly made a rookie mistake... thanks

 

[brandenclouse]

Re: unknown Knocking on mercruiser 3.0

basically I have called him as soon as i took it off the water.. to let him know what was going on, he seemed to be a pretty reasonable guy so will see what happenes. In my oppinion yes i believe he needs to make this right since he did say a shop did this.. he said he was looking into this for me.but who knows. Im looking to keep the boat just trying to figure out what is wrong with it. looking mostly to split cost or in some way help out with this problem.. if its something simple no big deal i just need to figure out how to diagnose the problem first. once again thanks everyone for your help

 

[fat fanny]

Re: unknown Knocking on mercruiser 3.0

Seems to be a common tale these days (not just with boats) but it always has to be a lesson learned. Maybe it could be possible to arrange some info for a stickie for the adults only section of the forum for do's and don't's on boat buying. Then it could help some of our fellow I-boat members and newbies avoid costly errors in thier purchases. But as far as the previous owner of this boat I would stay on him as said or you will most likely be eating the cost of these repairs.

 

[dsiekman]

Re: unknown Knocking on mercruiser 3.0

Maybe I'm just being the eternal optimist, but one of the exhaust flappers went on my last boat and sounded like a knock, not a tick. Cheap fix compared to pulling the engine.

Also, I would suggest you direct your anger at the mechanic who rebuilt the thing. Unfortunately, you bought from a private owner. You also ran the boat AFTER you bought it. If he is a stand up guy, he will at least act as an intermediary between you and the mechanic, though it is not really his responsibility. Your best bet in getting him to help is to let him know that you would appreciate his help rather than demanding your money back and calling him every name in the book...although I'm sure you would like to.

Good luck, and sorry to hear your first experience was not a good one. It happens to all of us.

 

[brandenclouse]

Re: unknown Knocking on mercruiser 3.0

thanks everyone for all their help on my issues... truely appriciate all the comment ...we just pulled the motor and found out we spun a rod bearing ..... can i get away with replacing one or should i replace all since i will everything esposed ...??? and should i go ahead and replace the mains too??? does anyone have a round about $$$ estimate on what these replacement cost thanks

 

[Bondo]

Re: unknown Knocking on mercruiser 3.0

we just pulled the motor and found out we spun a rod bearing ..... can i get away with replacing one or should i replace all since i will everything esposed ...??? and should i go ahead and replace the mains too??? does anyone have a round about $$$ estimate on what these replacement cost thanks

Ayuh,... That motor needs to go to a Machine Shop....
They can answer All your questions...
Just replacing the bearing shells ain't gonna fix a Thing.....

 

[6meter]

Re: unknown Knocking on mercruiser 3.0

The rod and crank journal is more than likely torn up and would need to be removed and turned. They usually don't survive after they've spun.

 

[coheej]

Re: unknown Knocking on mercruiser 3.0

If the crank is not worn too deeply, you could have just that one journal turned.
Personally, I don't like doing that because it can lead too screw ups by the next guy that has to open it up. The rod that was knocking should also be checked and most likely resized. Although not always done, the entire motor should be disassembled and cleaned to get the bearing material out of it.