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Knocking noise coming from engine area.

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Temple2426

Member
I just bought a 2005 MerCruiser 5.0. It has a knocking noise that is coming from the rear of the engine I think. It does it at idle and at higher RPMs.
In the water and out. Under load and in neutral. Foot up and foot down. It sounds like a hammer on a piece of wood. It has no rhythm and is not consistent it is erratic. Sometimes up to 30-40 seconds or longer between knocks and it may knock only two or three times in a row and quit then again several seconds later. Before I bought it the PO replaced the starter and fuel pump. Other than that there has been no other maintenance outside of oil changes and winterization that I know of other than I just replaced the risers and exhaust manifolds. This boat did spend some time in salt water in its early years.

Oil pressure is 40Lbs at idle
Compression test was great on all cylinders.
Fuel pressure checks out.

Any suggestions would be great.
Thanks!
 
Temple2426 said:
I just bought a 2005 MerCruiser 5.0. It has a knocking noise that is coming from the rear of the engine I think. It does it at idle and at higher RPMs.
In the water and out. Under load and in neutral. Foot up and foot down. It sounds like a hammer on a piece of wood. It has no rhythm and is not consistent it is erratic. Sometimes up to 30-40 seconds or longer between knocks and it may knock only two or three times in a row and quit then again several seconds later. Before I bought it the PO replaced the starter and fuel pump. Other than that there has been no other maintenance outside of oil changes and winterization that I know of other than I just replaced the risers and exhaust manifolds. This boat did spend some time in salt water in its early years.

Oil pressure is 40Lbs at idle
Compression test was great on all cylinders.
Fuel pressure checks out.

Any suggestions would be great.
Thanks!
Click to expand...
Pull the drive and examine the ujoints and gimbal bearing. You can shove a hose in the water port on the bellhousing and run the engine with drive off to confirm noise is gone.

Could be a bearing or gears in drive , if u joints look good pop the top cap of drive but my first guess would be u joints especially if u joints bellow have water in them
 
Thanks Dieter.
I read through some older post and saw where isolating the noise by removing the outdrive and serpentine belt. I did both and the noise is still in the block. I did pull in and out on the crank pulley and I have more than the allowable endplay. Its more like .080-.125 end play. That may be allowing the piston to slap or rods to bind as the crank floats. I will be puling the engine today for a rebuild.
Is there a place to by parts that is better than NAPA. I have used Engine Parts Warehouse over the years but wanted to check here and see what anyone suggested. Also any tips on pulling and rebuilding that I should know.
 
Temple2426 said:
I just bought a 2005 MerCruiser 5.0. It has a knocking noise that is coming from the rear of the engine I think. It does it at idle and at higher RPMs.
In the water and out. Under load and in neutral. Foot up and foot down. It sounds like a hammer on a piece of wood. It has no rhythm and is not consistent it is erratic. Sometimes up to 30-40 seconds or longer between knocks and it may knock only two or three times in a row and quit then again several seconds later. Before I bought it the PO replaced the starter and fuel pump. Other than that there has been no other maintenance outside of oil changes and winterization that I know of other than I just replaced the risers and exhaust manifolds. This boat did spend some time in salt water in its early years.

Oil pressure is 40Lbs at idle
Compression test was great on all cylinders.
Fuel pressure checks out.

Any suggestions would be great.
Thanks!
Click to expand...
Ask the seller if the U joints have been serviced- also, don't run the engine when the drive is tilted up fully. The U joints are supposed to be serviced on a regular basis and replaced if they make noise, especially if the boat is used on salt water.
 
Temple2426 said:
Thanks Dieter.
I read through some older post and saw where isolating the noise by removing the outdrive and serpentine belt. I did both and the noise is still in the block. I did pull in and out on the crank pulley and I have more than the allowable endplay. Its more like .080-.125 end play. That may be allowing the piston to slap or rods to bind as the crank floats. I will be puling the engine today for a rebuild.
Is there a place to by parts that is better than NAPA. I have used Engine Parts Warehouse over the years but wanted to check here and see what anyone suggested. Also any tips on pulling and rebuilding that I should know.
Click to expand...
Not sure if this ever got answered but Parts -

summit racing is great, also maybe if you just want a reman a place like michigan motorz .

If you have that much endplay who ever is machining it can get the parts. Often best to let machinist supply the parts in case their is an issue
 
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