Volvo Penta 5.7 GSi Knocking – Suggestions needed.

[DoubleDeuce]

A knocking sound coming from 5.7 GSI engine when accelerating to get the boat on plane. The noise does not exist when revving the engine or at idle speed. Only when accelerating to get on plane.
Few items to note:

• Third time out since coming out of winter storage
• New Plugs installed before last winter storage
• change prop to 4 blade aluminum
  • Since put back the 3 blade stainless to eliminate change
• Running premium gas only
• no leaks
• Oil is full
• Operating temp is normal
• no other leaks noticed.
• *** I have not checked outdrive fluid yet.

Thank you in advance for your suggestions.

 

[dubs283]

sounds nasty

could be a lean condition/detonation, check timing and fuel pump pressure throughout rpm range. probably time for a full tune up too

could also be internal engine issue but hard to tell from video

 

[DoubleDeuce]

sounds nasty

could be a lean condition/detonation, check timing and fuel pump pressure throughout rpm range. probably time for a full tune up too

could also be internal engine issue but hard to tell from video

I am wondering if it is a lean condition too. I just had a tune-up at the end of last season. I will check spark plugs etc...however, when it's sitting in the driveway with muffs on and I rev the motor, there is no such knocking sound. The knocking only occurs when in the water and driving forward faster than 2,000 RPMs. Could it be the outdrive? The knock sounds like it's in the engine, though.

 

[dubs283]

if it were the drive knocking that loud to be heard like that on a video i would guess the issue would quite apparent, however can't rule it out at this point

revving the engine on the muffs with no load won't tell you much, the engine doesn't need much fuel for that, even running lean won't necessarily expose an issue in that situation

the dynamics of the engine and drive are way different in the water with a load

GSI im guessing the engine is fuel injected, as stated, start with a fuel pressure test (with a load), also check fuel system vacuum - could have a restriction between the tank and the pump

 

[bruceb58]

Take your serpentine belt off and run it for just 30 seconds and do that same test to make sure its not associated with anything on the front of the engine.

 

[Scott Danforth]

When was the last time the drive was pulled and motor aligned?

 

[DoubleDeuce]

Take your serpentine belt off and run it for just 30 seconds and do that same test to make sure its not associated with anything on the front of the engine.

Interesting concept. I have a buddy who thinks it could be a bad impeller. The day the noise occurred, I was tubing my kids in shallow muddy water.

 

[DoubleDeuce]

When was the last time the drive was pulled and motor aligned?

Never, the engine is strong in the sense of no leaks, starts every time...well taken care of. But never pulled and aligned.

 

[Scott Danforth]

Never, the engine is strong in the sense of no leaks, starts every time...well taken care of. But never pulled and aligned.

that is an annual maintenance requirement

pull the drive, inspect the gimbal bearing, inspect the u-joints and check alignment. every 100 hours or annually, which ever occurs first.

 

[Bt Doctur]

That tinny sound sounds more like a loose rocker arm/pushrod/failed lifter

 

[DoubleDeuce]

RESOLUTION:
Unfortunately, it is not good. After a compression test, Cylinders 4 & 6 only held 50 psi while the rest were 180 psi.
New head gasket, both heads machined and cleaned, all new plugs, oil, and a plethora of other items. Sadly, we are out of the water for at least three weeks! Thank you, everyone, for your suggestions and for sharing ideas.