Engine knocking, can't figure it out.

[AlanGreyjoy]

Hey guys,

So my engine is knocking like hell.

installed a new lower chain tensioner about a month ago, but no change.

Thought the sounds was coming from the water pump, changed that, no change.

The knock will go away completely after 3k rpms, but it comes back once the rpms come down.

Any ideas? Any suggestions?

youtube video
https://www.youtube.com/watch?v=WOcvfF8NpXg

[monty23psk]

Sounds like your chain tensioner.

[AlanGreyjoy]

Sounds like your chain tensioner.

You mean to one I just replaced?

[monty23psk]

It sounds chain related, as the chain is spinning and loose/rubbing. One of your guides or sprockets might also be loose or something related to that. Does the sound get louder as you accelerator. If so, then its something with the chain in my opinion.

[Tgoode318]

man that poor m42, that is some hellacious chain slap! Monty is on the right track bad guides perhaps.. You will need to open her up and inspect the components. Also when you replaced the tensioner did it improve at all?

[colin86325]

It does sound chain related.  Strangely enough, I had a similar problem where there was a rattling noise.  I automatically assumed it was the timing chain/components, but it turned out to be the water pump.    I was expecting the water pump failure mode to be a squeeking/chirping noise, but in my case it sounded like a timing chain problem.
See if you can wiggle the pump pulley/fan to expose any play in the pump.

[AlanGreyjoy]

When I replaced the lower tensioner, the noise got really nasty, then settled down like normal. But... it did seem to be louder than before lol.

I thought the sounds was coming from the water pump. When I had the hood on, the sounds was coming straight from there, or so I thought. I replaced the water pump, the knocking is still there.

The sound seems to come from the intake lmao. Or under it. Which I am thinking it's a rod bearing. The one that connects to the crank (not sure of the exact name).

So, to inspect the chain, i take off the valve cover and the entire front case? Are there any write ups on chain inspecting for our motors?

Does a rod bearing sound out of the question?

I assume all I need to do is drop the oil pan and start tugging on them and see if they move.

I know it's an old motor. I have thought of doing a swap... but I love my m42

Also, the sounds stays the same pitch when I accelerated. But after 3k rpms, it goes away 100%

[AlanGreyjoy]

Ok...

So how much play should there be on the chain? I can grab the chain on the right side, and it will pull off the sprocket and touch the side of the case.... this may in fact be what we are hearing. Is that to much play?

Taking the case bolts off now... but missing my giant wrench to take the stupid fan off lol.

[colin86325]

Yes, that sounds like too much slack.
I'm thinking one of the rails or the bottom sprocket/bearing has broken.

[AlanGreyjoy]

Yes, that sounds like too much slack.
I'm thinking one of the rails or the bottom sprocket/bearing has broken.

yup... holy shit man... I don't even have the side guide rail anymore! It's.... just half of one lol. The damn chain dug into the case as well. About to remove the lower case as well. I was not prepaired to remove so much stuff. And as always when working on cars, that one tool you NEVER use, is missing. #23 socket for the crank.

[AlanGreyjoy]

I'd also like to note.. that ever since I bought the car (4 years ago) it has never ever hit normal operating temperature. I just assumed it was a bad sensor.

Boy was I wrong.

I found that the t-stat is broken and stuck open. Jesus... good thing I don't have a cat or an o2 sensor. This explains the horrible horrible gas mileage I get. I just assumed it had bad gas mileage becasue of the chip the PO had put in it.

Guess I need to stop assuming so damn much.