I got a 4K-U engine, and I need help identifying what might be the problem, as the engine makes this noise which sounds like coming from high up the engine, in the valve cover area. This noise is only noticeable when revving aggressively to high rpms, but when driving normally, I don't hear it from the vehicle cabin (or it might still be making noises, just not audible inside the cabin).

aggressively revving to 3500 rpms

Here is how it sounds like in normal conditions under 3000 rpms

Rpms is meter reading x10

The oil was newly replaced, and I have been using the same 20W-40 oil that I have been using on this car all the time.

 

 

Edited January 11, 20251 yr by xtianthrow

Which noise??? Sounds like a K motor, a bucket of bolts! 

You are free-revving it so all the slack in the bearings, the timing chain, the piston slap, the valve train.. all are knocking back and forth as it is not loaded. When you drive it all those noises vanish as the motor is being forced in one rotation direction.

What are the noises like around 70kph and 90kph when you are -

Accelerating normally?

Cruising at that speed?

Decelerating slightly?

Have you checked the tappet gaps? ..and the wear in the rockers where they rub on the valve? If they are grooved then feeler gauges will give you the wrong readings. Same with wear in the rocker bushes where they rotate on the shaft, the valve spring forces the rocker up against the bottom of the shaft but when the tappet gap appears the rocker can bounce up and down for a moment.

Edited January 11, 20251 yr by altezzaclub

14 minutes ago, altezzaclub said:

Which noise??? Sounds like a K motor, a bucket of bolts! 

You are free-revving it so all the slack in the bearings, the timing chain, the piston slap, the valve train.. all are knocking back and forth as it is not loaded. When you drive it all those noises vanish as the motor is being forced in one rotation direction.

What are the noises like around 70kph and 90kph when you are -

Accelerating normally?

Cruising at that speed?

Decelerating slightly?

In the video link I posted, it's the momentary high pitch metal sounds (happens when the meter reads 350). Almost sounds like loose bolts, or grinding metal?

I never really ran this enigne at high speeds, and I mostly keep rpms below 3000, most I think is 50 kph. The "noise" that I am concerned isn't really audible at least when I'm in the cabin.
The video doesn't quite catch it, but it's quite jarring to hear when revving the engine with the hood up. I don't recall that "noise" being present before though, so I am worried something might be getting loose.

I was suspecting valve clearences, since the shade tree mechanic did the tappet clearances maybe 2 years ago, and I don't know what feeler gauges settings he did.

Edited January 11, 20251 yr by xtianthrow

I would suggest that you remove the rocker cover, & then start the engine, without the rocker cover, if nothing visually, immediately appears to be amiss.

You will probably find a tappet adjustment, that has come loose, or maybe a cracked or broken valve spring.

Let us know what you find. Just check that the sheet metal on the inside top of the rocker cover, has not come loose at one point, so that it vibrates at certain high revs.

Cheers Banjo

 

 

Well, buy yourself a set of feeler gauges and away you go! 10thou and 12thou from what I remember, or 8 & 10 depending if the motor is cold or warmed up. The exhaust valves have a slightly larger clearance as they expand more in the stem as they run hotter, and you need to always have a gap when the valve is closed or you burn the valve out..

I expect you would hear a loose tappet before those rpm, but I can't suggest any particular thing making that noise.  Under the bonnet sounds terrible on any old car, especially as they are empty revs rather than the motor actually working. Its not some loose heat shield panel or similar is it?

If you rev an engine in a slow curve there is a longer period around the top when it is floating, neither being accelerated nor decelerated. That is the time is is noisiest. If you rev it up and down sharply its is either being pushed or pulled, and you won't hear the noises so much. The harmonics change with rpm so motors get buzzy at a certain range then it vanishes. The 3SGE motors were terrible at 3000rpm as you lifted off the accelerator, the buzz sound would reverberate through the Altezza.

If it has piston slap or loose bearings you hear the tapping or knocking quite clearly in my experience.