Identify that sound, fresh engine death rattles edition

I've already arranged to get the engine pulled apart in the next few days to find out exactly what it is, but that's a lot of suspense.

The 4AGE started making a noise while I was just cruising along, sounds a lot like rod knock. It doesn't get louder with revs, change on rising/falling revs, or get noticeably quieter with spark cut to any of the cylinders. I drove gently and shut down just a few seconds after the noise started, but there was no noticeable loss of power and the engine still idles fine (I've run it for a couple of minutes, with the car parked, to let mechanics have a listen). The guy who built it had a listen with an automotive stethoscope and found that it was loudest around the valvetrain area. The engine is bone-stock internally apart from a thinner head gasket and some deburred oil passages.

Any ideas?

stumped based on

GameboyRMH said: It doesn't get louder with revs, change on rising/falling revs, or get noticeably quieter with spark cut to any of the cylinders.

Can he/you determine where in the valve train? isolate to front 2, or rear 2 cylinders?

I could probably find a medical stethoscope and give it a try, but I'm not gonna hear from the builder again until he takes the car into his shop.

Could it be a sticking valve?

I'd pull the spark plugs to make sure their insulation was still attached. I'd also pull the valve cover just to look and admire things. Good chance in one of those two locations you're going to find something.

I had a core drop out of my spark plug that made a similar noise. Eventually it found its way out the exhaust valve, but there were definite running issues with that one

You can use a long screwdriver or socket extension in place of the stethoscope. Press one end up against your ear, the other on various parts of the running motor. Works about as good as the $5 mechanic's stethoscopes. FYI, the first true medical stethoscopes were wooden cylinders, maybe 6-8" long, maybe 1" diameter.

OK, got a plan for tonight:

1. Stick neodymium magnet to oil pan...for safety (ordered a magnetic drain bolt already but won't have it for a while).
2. Check spark plugs
3. Run with screwdriver stethoscope, take video this time
4. Post video
5. Maybe remove valve covers and see if anything is obviously wrong

This is a 16 valve motor, right? Listen on the exhaust and intake sides of the head, both outside the spark plug area and inside. Using the long screwdriver, press the handle firmly against your ear, then prod around with the other end.

This is a long shot...Check the bolts that hold on the water pump pulley.

Pull drain pan. If you see large bits, begin depression/sadness pill regimen.

Only had time to do 1 and 2 tonight

At least I can rule out a broken-off chunk of insulator, would've been dumb to tow the car to a shop over that. I had a peek down the spark plug holes, I didn't see any debris but I did see a smear/scuff mark in the soot on the #3 piston, near the center. Don't know if that means anything.

Got one more thing done, I managed to get a spanner around the water pump pulley bolts, even though it's clearly not meant to be possible while the upper radiator hose is in place. When I try to tighten them, the pulley starts to slip against the belt first, so they're not too loose.

Drain oil into mason jar, use a magnet on the outside to see if you can find shiney bits if you cant see any with the naked eye.

But you said the noise doesnt change with rpm, does it change at speed?

Could be loose flywheel bolts? Ive seen cars do that and sounds like rod knock. You do have a harmonic balancer on the motor and not one of those fancy underdrive pullies right?

I had that exact flywheel bolt problem just a couple of months ago in fact, it was sort of like this but more of a loose rattling noise. I am running a fancy pulley, not underdrive but it's solid aluminum with a trigger wheel.

If your bottom end is coming apart, you should be able to visually see and smell it in the oil. A spun bearing generates a LOT of heat...hate that smell. Drain it, take a sample, send it to Blackstone for analysis if you really want to go all-out.

How's your oil pressure?

Oil pressure isn't low enough to trigger the idiot light, that's all I know.

I'd rather leave the oil in until the car goes into the shop, I don't want to do anything that could "destroy evidence." Once it's out though and the builder has a look, I'll run it all through some filters and see what comes out. And cut the oil filter open as well.

Do you have A/C? The compressor pulley on my wife's Fit self destructed and made some very concerning noises. I ended up getting it towed to a shop for many of the same reasons you list above - wasn't correlated to revs, load, or anything else. Since it was the bearings in the pulley itself, didn't change if I turned the A/C on or off either.

Good luck! Hopefully it's something non-catastrophic.

It does have AC and I'm well-acquainted with the sound of a failing AC compressor bearing - more of a grinding/whining noise. This is more of a knocking noise, it does change frequency with revs but not volume.

Broken valve spring?

If it was a civic is say it was an input shaft bearing. But I'd check your a/c clutch and your water pump main bearing. I had one go it made a horrible racket.

I'd think a broken valve spring would cause some obvious performance problems...the engine's still running just as well as it always did, at least in very gentle driving and idling which is all I did since the noise started. I'd think a broken valve would feel more like losing spark to a cylinder.

The water pump only has a few hours of runtime on it, same as the engine, and it's a Toyota unit. The AC pulley bearing on the other hand is no spring chicken but the noise is definitely not coming from that area.

GameboyRMH wrote: This is more of a knocking noise, it does change frequency with revs but not volume.

did you ever get it video-ed??

Didn't have time last night, I'll do it tonight. By frequency I mean the number of knocks per second, not the tone.