Engine Knock Merc 165HP - Help!!

[Brooksie]

Hi All;

My impeller failed while I went to the car and came back to a mess.

I've replaced every gasket and re-did everything outside the block.

The motor runs quite well now - but at 2000 RPM and above I get a knock that gets louder and faster with additional RPM. It seems to me to be timed with a rocker. I've had it running with the valve covers off and eliminated any noise from the rockers. The noise seems to be coming from underneath the heads in around the 5th or 6th cylinder.

I did re-build the fuel pump as well - I know that this can cause a knock - but at higher rpm - she gets pretty darn loud.

I've pulled every pushrod and can't find any sign of damage or excessive wear.

Please help me identify what the failure may be.

Also, I'm trying to determine where the hydraulic valve lifters are and how to inspect them without pulling the motor.

Your help is appreciated!

Chris

 

[Haut Medoc]

Re: Engine Knock Merc 165HP - Help!!

Knock is usually a bearing.......
Try disconnecting the plugs one at a time.....
You should be able to determine what cylinder is affected using this method.....​

 

[Coors]

Re: Engine Knock Merc 165HP - Help!!

Does the knock get quieter when you let off the throttle? = rod bearing shot, along with that crank journal, and rod. The piston should be ok.

 

[Brooksie]

Re: Engine Knock Merc 165HP - Help!!

ok - I will pull a plug at a time and run it to see if the noise dissapears
If the noise stays after doing all 6 - what is the next likely cause?

with the heads off - I do not see the lifters exposed - please tell me you don't have to pull the engine out. How are they best inspected?

the higher the rpm - the louder the knock so yes - lower rpm there is no knock

Can you explain this part a bit more? "= rod bearing shot, along with that crank journal, and rod."

Many many thanks

 

[Coors]

Re: Engine Knock Merc 165HP - Help!!

When the rod bearing goes, 1/2 of the shell moves, putting grooves on the crank journal; or it is so loose that it beats the crank journal out of round. no matter which, the rod is shot, as it can't hold the bearing correctly anymore.

 

[Brooksie]

Re: Engine Knock Merc 165HP - Help!!

I'm sorry for being confused. Are you saying the push rod? Or are you refferring to the cam itself?

this is how I know the parts - front top to bottom

rocker
push rod
valve lifter
cam

where are you saying the failure is?

Many many thanks.

 

[180shabah]

Re: Engine Knock Merc 165HP - Help!!

I agree, you will probably be rebuilding the bottom end.

 

[Coors]

Re: Engine Knock Merc 165HP - Help!!

The connecting rod to the piston.

 

[Brooksie]

Re: Engine Knock Merc 165HP - Help!!

ugh - are you telling me you think it's the crank shaft??

The one thing I need to know as well is at what point do I pull the motor out? Needless to say, that's a tough one. I was hoping to inspect further than the push rods without having to pull the motor.

what do you think?

 

[Brooksie]

Re: Engine Knock Merc 165HP - Help!!

lol - I had my head so stuck on it being in the valve train. But I never thought of the connecting rod from the crank to the piston.

If it IS the connecting rod - pulling a spark plug one at a time and then the noise is gone - indicates a bad connecting rod / bearing - correct?

If the noise stays after going through all 6 cylinders - is it more likely the valve train?

I've also heard that the fuel pump can knock - but this seems a little too loud to be that.

let me know and thank you.

 

[Coors]

Re: Engine Knock Merc 165HP - Help!!

wait; are you sure it is not in the valve train? Get a good manual and make sure your lifter isn't collapsed. It takes a height gauge.

 

[Brooksie]

Re: Engine Knock Merc 165HP - Help!!

I do have a manual and it points to lifters and valves.

I will service the heads to make sure of that part.

But my question in the beginning was - how do I get to the hydraulic valve lifters?? I was expecting to see them exposed when the head came off.

Please let me know - I really need to check this before I pull the motor out.

 

[Bondo]

Re: Engine Knock Merc 165HP - Help!!

But my question in the beginning was - how do I get to the hydraulic valve lifters?? I was expecting to see them exposed when the head came off.

The Lifters are Behind the Side Covers.............Along side, Both sides of the Distributer......


Btw,..........

Do the Sparkplug Wire Test like Haut said,..........

I'm Thinkin it's a Rod Bearing...........

 

[Brooksie]

Re: Engine Knock Merc 165HP - Help!!

Awesome I will do that for sure. I of course am hoping that I don't have to pull the motor. Is it as tough as I'm thinking or not 'too' bad?

Many thanks for the help

 

[Bondo]

Re: Engine Knock Merc 165HP - Help!!

Compared to Yanking the engine from a Car,...........

Hauling a Boat Motor is a Cake Walk.........

 

[Brooksie]

Re: Engine Knock Merc 165HP - Help!!

I'm trying to find instructions in my merc manul for how to remove the valve lifters thru the side access - is it pretty obvious once you get in there? I don't want to open a can of worms and not be able to get them back in there. I would have thought the cam would need to be out of the way.

I'm hoping also if I can identify a damaged rod thru the side covers.

I'll let you know how it goes - open to 'any' suggestions and really appreciate this great help.

 

[Bondo]

Re: Engine Knock Merc 165HP - Help!!

Btw,..........

Do the Sparkplug Wire Test like Haut said,..........

I'm Thinkin it's a Rod Bearing...........

There Ain't No peeking thru any windows..........

 

[Brooksie]

Re: Engine Knock Merc 165HP - Help!!

Compared to Yanking the engine from a Car,...........

Hauling a Boat Motor is a Cake Walk.........

lol - well - I feel much more confident now - I really appreciate the feedback.

Reading the merc manual - it describes knocks that are 1/2 motor time to be in the valve train - knocks that are more in tune with the exact rpm of the motor tends to be in the crank which makes sense given the gear ratio. This is what is pointing me there.

I am going to follow all the steps you have recommended - and will deffinitley be back!

thanks again

 

[Brooksie]

Re: Engine Knock Merc 165HP - Help!!

hahaha ok... wishfull thinking. Trust me, I will be following your suggestions to the T. But when the side covers come off - I don't have to worry about any surprises pulling the valve lifters? I don't want springs flying thru the air or nuts in my oil pan. lol

 

[SuperNova]

Re: Engine Knock Merc 165HP - Help!!

you have to pull the valve cover first and unbolt all the rocker arms, then remove the pushrods, then you can go in through the sidecover to remove the lifters.
--
Stan