rod knock

Rod knock, valve clatter, oil pressure, engine compression and mental health

If you have been watching my YouTube channel your probably now that my engine developed a weird noise and failed. It’s time for that information to hit the blog and I tell you the long story of my engine’s failure.

How it all started

The first time I noticed the noise coming from my engine was when I was driving through a tunnel, and accelerated mildly. I could hear knocking sound bouncing off the tunnel walls and back into my ears. At that moment I could have sworn the sound was actually pre-ignition because it followed engine speed, i.e. the rpms.

I planned to do a longer drive but I turned around straight away and headed back to the garage, face all pale. I could tell the sound was bad and that it wasn’t something to be taken lightly. Rod knock came to mind, but I dismissed it instinctively for the sake of my mental health. I mean I was so careful with everything. The machine shop measured everything and then I even plastigaged once after them to make sure. Please God don’t let it be rod knock. I didn’t sleep too well that night.

The next day I decided that I was going to do a series of tests to check everything on my engine to identify once and for all what is wrong.


I started with the compression. I knew bad compression couldn’t be really making a knocking noise in the engine, but a compression test was long overdue and I wanted to see how my rebuilt engine was doing.
Doing a compression test is easy and so cheap that you can do it yourself. All you need is a cheap compression tester from eBay that has the right adapter for the size of your spark plug thread.

Here’s the video. Videos are more fun than reading.

My compression turned out to be 160 psi on all cylinders. I actually forgot to test with the throttle wide open the first time around so my numbers looked pretty bad. I was super relieved that I forgot to keep the throttle wide open during the test. 160 psi on all cylinders is actually right on the money seeing that 148 is the minimum and 179 the maximum for the 4age. What’s even more important than the number is the actual difference between the cylinders. In my case all cylinders were the same and that made me really happy 🙂

Is it valve clatter? God let it be valve clatter.

Once I got back to the garage from that god-awful drive during which I noticed the noise I listened carefully to the engine to try and pinpoint where the noise is coming from. The sound seemed to be coming right from the head and that kind of reassured me that maybe it’s just the valve shims being out of adjustment? But I knew the chances for that were stupidly slim because the machine shop reset all the shims to the sizes from the BGB. But I wanted to be sure it’s not valve clatter so I got the valve covers off and tested valve clearance.

Here’s a video on how to do that:

The bad news was that all my valve clearances were spot on. I was happy that the machine shop did a good job, but this eliminated one more probable cause of the noise and the spotlight crept ever closer to rod knock.

Is it the t-vis plates? God let it be the t-vis plates

Every time I went to the garage I would fire up the engine, rev it a bit and listen closely in the attempt to identify the source of the noise ( I now know that’s unfortunately a fool’s errand since engines make so many noises and the average human ear is a very poor tool to separate and isolate each of them). Since the valve noise was eliminated I started thinking that the noise is coming from the injectors (see how the human ear poor tool comment above makes sense?). That hope died too because the noise did not go away as I unplugged each of the injectors with the engine running.

I then read online that the t-vis plates in the 4age engine can make a noise very similar to rod knock. Hope appeared in my mind again. All blissful and dressed in white. With large puppy eyes we looked together at the gods to grant us our wish and let my t-vis plated be faulty instead of my engine block. I unplugged the t-vis connector (right underneath the intake manifold) and voila the engine sound at idle changed noticeably. A very weird clackety noise disappeared. But the knocking noise was still there. Clearly audible. The gods granted the first half of the wish, the t-vis plates were faulty, but it seemed my engine block was too. Hope patted my back.

Oil pressure

It was time to start heading down the path of looking at rod knock. The first sign of rod knock is actually bad oil pressure. This too can be measured in the diy home-mechanic arrangement with the help of cheap eBay stuff. I ordered a manual oil pressure gauge from eBay for another sub 20 dollar price and as soon as I got it hooked it up to my engine.

Here’s another educational instructional video:

When I first saw the oil pressure figure I was mega happy. My oil pressure was beautifully within specs. Hope smiled and ran through my mind with a basket full of flower petals, scattering them enthusiastically over my neurons. Hope never abandon me again. My manual oil pressure gauge needle was a bit bouncy, but I decided not to let that bum me out and I blamed it on my cheap oil pressure gauge. I filmed the last part of the video showing my happiness and eliminating rod knock as the cause of my horrible engine noise.

After I got home I decided to research the bouncy needle a bit, you know, just in case. I realized it was unfortunately far more menacing than I thought and it often meant that oil was escaping somewhere and could point in the direction of early stages of rod knock. Hope is wounded. Hope, she is bleeding. I deleted the footage I planned to close the video with and recorded only audio, expressing mild concern over the bouncy needle.

Is it really rod knock? God please don’t let it be rod knock

I realized there was no more putting it off. I got the car on my ramps, drained my very new oil and unbolted the oil pan. No better way to know how the rod bearings are doing than looking at them.

Once I removed the oil pan and got access to the rod bearings I first shook the connecting rods to see if they were loose. They were rock solid. Ok, so it’s not a disaster. Hope stood up, her legs were wobbly but her expression still determined, as if saying “I am not going down yet”.

So I got my socket wrench and unbolted a connecting rod cap and finally took a direct look at my rod bearings. Disaster. The bearings had obvious signs of damage. Most of the copper layer was already scraped away.

I looked at hope with an expression of horror on my face. She smiled softy, fell to the ground and died. I shook her motionless body yelling “Why did you stick around for so long you stupid woman????”. Indeed, hope dies last. But she dies nevertheless.

Here’s yet another video. It’s full of rod knock. Not for the feeble.

When I saw my effed up rod bearings for the first time I was surprised that I didn’t lose it. I was super calm. It’s like those moments when they tell you someone close to you has died. For me it’s not like in the movies when people start yelling and screaming right away. My mind refuses the reality of such information and takes it in only bit by bit over a longer period of time. I like to believe it’s a system devised to avoid mental self-destruction. Or maybe I’m just slow?

Why did my rod bearings fail? I don’t know yet, but I do intent to find out. Rest assured the causes will be revealed in their entirety.

What now? Well, fortunately engines aren’t fleshy fragile people and they can be rebuilt. I found solace in the fact that every failure is an opportunity and decided to make lemonade out lemons. Soon my plans will be revealed.

Until then, stay tuned and thanks for reading.


2 thoughts on “Rod knock, valve clatter, oil pressure, engine compression and mental health

  1. I’ve been following your build for a while, I know it must be dissapointing but atleast you know what the issue is, and before it could cause other damage. Did you measure your bearing clearances with plastigauge? Did you use any assembly lube on the con-rod bearings?

    1. Thank you for following the build. I did measure everything with plastigauge, and used assembly lube wherever needed.
      My engine failed because of blast media that I did not wash out of my block properly. A really lame reason, but that’s life I guess.

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