3rz engine rattle/knock smoother idle?

So my issue is a fairly loud metallic "marbles" rattling in the motor. One day it started and was like that for 400kms! Rattling while cruising and less at idle. Less frequent or none under load. And the moment this started the idle changed to a noticeably smooth idle even at the same rpm. Normally my truck has always idled at 750 but a lot of vibration. Now very smooth.
When it's revving up under load it's so smooth it feels restricted, but no loss of power.
A shop quickly listened and said slack timing chain for sure. But now the noise stopped for another 300kms, and everything was "normal" just a good ol 525,000 km 3rz
But today it started again! Same symptoms.
How could a timing chain become slack and affect the timing to smooth out the idle?
Tensioner is failing? Possible
Low oil pressure? Tensioner is dependent on oil pressure?
Just did an oil change. No metal shavings in the pan. Did not cut the filter though.
In my worry I did just pickup a new 3rz to swap in if it fails.
Is this motor an interference motor? Will it be wrecked if the chain breaks?

Thanks for any help!

 

It could be the timing chain has some slack and is slapping around in there. But I'm not entirely sure, but I think those chains can stretch over time, albeit a long time.

 

Yes it is very old. I was sure that was the issue Untill it stopped and fixed itself and now has returned. If it was stretched it would stay stretched would it not.. Haha

 

Pretty sure our trucks are non interference motors...should be fine if the chain fails.

 

Yeah the fact that it comes and goes is weird. And I think bry838 is right, even if the chain fails, it shouldn't be catastrophic. Of course, it could be an entirely different issue. But with no metal in the oil it makes me think it must not be in the motor, but without hearing it personally its a little harder to diagnose.

 

could just be detonation clatter going on, but if that were it, its strange you don't have any CEL going on.

check your timing any see if it stays steady or floats, if it floats it could be a sign of stretched or loose chain. I suppose its possible you broke a chain guide and it finally fell off into the pan. they are made of plastic so there would be no metal.

 

How can I check for a floating timing? Check it now with the issue and again if it stops? With my obd2 reader I think it will tell me timing or some degrees

 

put the timing light on it at a steady idle and watch the line, it should stay pretty steady at the same mark give or take 1/8" but if its moving 1/4" or more then it could indicate too much slack, that could be fore several reasons but it just means it doesn't have a steady tension on it.

it literally is like it sounds, the mark will float up and down as it takes up the slack and then loosens again. it will be slow enough to see like a wave action

 

should here my 2.7 on them cold mornings, sounds like a rods bout to exit the block but she's still purrin along

 

This is incorrect. Toyota 20R, 22R, 22RE, 22RET, 2RZ-RE, 3RZ-FE engines are all chain driven interference engines. If the chain fails, the valves and pistons will be damaged.

The 5VZ-FE and the 3VZE is a belt driven non-interference engine. Therefore the valves can not come in contact with the pistons if the timing is not correct.

 

This is correct, my bad. I was under the assumption that the belt driven motors were interference motors but the 3RZ-FE is an interference motor. Defiantly don't want that chain failing, if that's what is making noise.

 

Whoops! Sorry OP, guess I should keep my mouth shut!

 

New information! I noticed that the marbles come to surface when I get low on gas! The first time I was below 1/4. Even after I filled it and drove 300km it rattled the whole way then stopped after another fill! Everything was normal Untill again below 1/4 it started. Filled up today drove 100m and it stopped again!
But if there was a fuel issue why would it run so smooth and have no noticeable power loss.. Crappy gas in the bottom of the tank? Water in there?

 

youngtoyo-
it may be water in the tank, what octane do you run in your car?

on a side note i have a 2.7L that makes the same noise. only at idle, goes away under load.

kinda sounds like i have a desiel.

apparently the previous owner had a mechanic tell him it was the timing chain guide, so he replaced the timing chain and guide, and the sound still was there.

ive noticed that the sound gets louder when its colder outside. and in the middle of the summer after driving for 2+ hours, the rattling is almost gone.

I've tried putting lucos oil with my oil changes, zero change, rattle still there.

i think that one of the pistons broke there skirt off, and during idle the piston is slapping the side of the cylinders, and when the motor is seeing load the piston either straightens up or rides one of the walls of the cylinder, stopping the rattling.

i won't know if this is true until, i find a doner motor and take apart my old 2.7L

anyone else experiencing this rattling with the 2.7L??

 

Interesting. Mine is unlike a diesel though. Just sounds like a broken motor.. A very bad sound, I put a screwdriver stethoscope on and I feel like I get most clatter at the front/ upper motor. My money is still on timing chain slap.
I've read that there can be issues with the balance shafts aswell. Might be worth a delete on my new motor sitting in the garage.

 

Not sure..

 

what are balance shafts?

 

I believe they are a weighted shaft ran off a chain that rotates and helps to offset the vibrations of our large displacement 4cyl motors. People sometimes remove them to gain a few HP possibly 5-10hp. And the vibrations are then increased but not enough to be teeth rattling or discomforting I've read. Lce sells a kit to delete.