Very loud rapping but oil pressure good and no loss of power...

[frankstower]

While on the water yesterday I had some trouble with the ignition, points, condenser... changes those as well as spark plugs. Oh, and the fuel filter, again!
Finally it's running great, planes off quickly and accelerating great. Approaching 35 mph the engine starts making this incredibly loud knocking, like someone was inside the valve cover banging it with a hammer...repeatedly. Limped it back to shore but never lost oil pressure or power. Even gave it some throttle and the power was right there instantly.
Got it home today and can feel/hear the rapping in one of the two back cylinders. (it's a 4 cyl. 224 Ford motor) Still, just like somebody is tapping the backside of the valve cover VERY loudly!
I've been told it could be 101 different things, some not so bad but others telling me it's now an anchor. I don't know much but to me it would seem it can't be much more than a rocker arm or bent rod if the oil pressure stays up and there's no loss of power??

Any suggestions from some of you who actually know something?!

Thanks in advance for any help.

 

[Uraijit]

Re: Very loud rapping but oil pressure good and no loss of power...

Usually valve train noises are more of a tapping sound, than an "incredibly loud knocking".

Start by pulling your valve covers, and see if everything is cool there. I'm betting it's on the bottom end though

 

[chiefalen]

Re: Very loud rapping but oil pressure good and no loss of power...

Sir: can we get some accurate info here from you. Make, model, year would be helpful. Same info. on out drive.

Thank you.

 

[Big Boat Bay Buster]

Re: Very loud rapping but oil pressure good and no loss of power...

I do like the 470, but one of its problems are, it like to ingest water which usually finds its way into #4. Common cause is a clogged riser. Any evidence of water in the back cylinders? (steam cleaned sparkplugs). You won't know anything for sure until you start tearing into the motor. Take the valve cover and the side lifter cover off and see if anything is loose, go from there. If it does appear to be a rod bearing, perhaps you can pull the engine, drop the pan and change the bearings, since you state the rest of the engine appears to run fine. Most people here will advise against this since its a 470 and not a politically correct way to do an engine repair. Anyhow, GOOD LUCK
My 2 cents, Chris

 

[frankstower]

Re: Very loud rapping but oil pressure good and no loss of power...

So I had my engine looked at and sure enough, number 1 cylinder is where the noise is coming from. First of all the spark plug had broken off (piston traveled too far up apparently) that's what the ungodly sound was....now it's just a tapping sound. Still runs, same power and pressure but bearing or rod definitely on the way out. Suggested that I use it for vacation, which just ended, and rebuild over the winter. (Oh, and it's a 1986 four winns with 170 merc. I.O.)
Ran ok for the first two days but had more problems which I'll post in a new thread. Thanks to those who answered my original question.

 

[Don S]

Re: Very loud rapping but oil pressure good and no loss of power...

I seriously doubt the piston is traveling too far. More likely a valve broke off and destroyed things in the cylinder, including the sparkplug, head, piston, and most likely the cylinder wall.
The valve is probably buried in the piston.
DO NOT run it anymore. Pull the head and look.

 

[mthieme]

Re: Very loud rapping but oil pressure good and no loss of power...

He said he changed the spark plugs...perhaps with ones too long (?) and piston and/or valve was hitting it.
He also said it still ran good so the valves are still attached and seating.
He said it was a heavier sound so I suspect a piston hitting a plug.
Assuming this is the problem, it should have happened on all cylinders.
Just speculating...

 

[Don S]

Re: Very loud rapping but oil pressure good and no loss of power...

He also said it still ran good so the valves are still attached and seating.

I've had WAY too many customers come into the shop saying there engine ran and sounded great at idle, only to listen myself and could hear a dead miss. Only to do a compression test and find one or more cylinders with zero compression.
Had one guy says it ran fine, just smoked a little, and no noise. No compression on #8, found complete piston missing when I pulled the head. Rings were in the cylinder and the rod was showing. I'll look, because I used to have a picture of that cylinder.

 

[qystan]

Re: Very loud rapping but oil pressure good and no loss of power...

I've had WAY too many customers come into the shop saying there engine ran and sounded great at idle, only to listen myself and could hear a dead miss. Only to do a compression test and find one or more cylinders with zero compression.

Personal experience. Merc 5.7 engine "ran fine", a little sluggish but can't exactly finger it. Always had some water in the oil. Finally gave in to the water problem and got a reman long block. Did one last comp check before pulling it, #2, 4, cyl had 30-40psi, #8 60psi. So much for an engine that ran fine - only exhibited mild vib at idle and slight hunting idle +/-20rpm and quite responsive to the throttle.

Best decision to date, now getting close to 1 mile per liter, previous best was close to half a mile to a liter. Lesson here - never believe in 'runs fine!