!jz knocking sound

[Supradupra.com]

Yes, I meant the factory idle speed for the 1j from cold is unusually high, between 1200-1500 RPM, unusual.

We too thought piston slap at first but, as above, it's not really the correct sound.

It could be some sort of effect caused by all these modern super sticky, cleaning, synthetic oils maybe?


I would not say it's a worrying sound, would just be curious to know what it is, I suspect we will never know. You only have to take any modern multi valve engine from cold & they all sound like a bag of nails was deposited in the rocker cover when first started, horrid.

 

[te72]

I always thought the 1j idled kinda low on cold startup, personally. But then again, I've owned a lot of 4 cylinder cars. Mazdas in particular, they idle around 2k cold, which did kinda worry me, but I guess it works for them.

 

[Loose Seal]

Good timing...I'm in the same boat. While my build is relatively new, I had it running multiple times late last season and didn't notice it. This spring it is very noticeable, all the same traits as posted earlier. Was thinking valvetrain as knock just didn't make sense (and my knock readings on the PFC are not moving, though I need to verify those are actually operational).

 

[geartech]

Did a comparison of pressure on the gauge vs mechanical gauge. It looks like the one in the dash is 1/2 of the real pressure on the mechanical gauge.
Anyone seen this?
There appears to be two different senders for the 7mgte wonder if the wrong one can cause this?

 

[OneJSupra]

If the serpentine belt tensioner is bad, it will make that sound when cold.

x2

 

[Ryan_V]

When my tensioner was going bad I could quickly snap the butterfly at the throttlebody and you could really hear the tensioner complain. Blah da dat...

I was also recently fooled by a power steering pump into thinking I had a rodknock. I got out there with a stethoscope and you could hear the pump loud and clear making the noise. Only thing is it got louder once the car warmed so probably not your issue...but who knows.

 

[te72]

Interesting... so, thinking along the lines of the tensioner being the culprit, the belt should be a bit on the loose side if my tensioner is on it's way out, correct?

 

[Dylan JZ]

x2

x3

 

[SUPRARICE87]

I KNOW THE 2JZ HAS A FORGED CRANK AND RODS, BUT BE SAFE THAN SORRY!! I would check oil see if you spun a bearing. check it, it won't go away but it will get worst!!

 

[te72]

It's definitely not rod knock, kinda a different sound, and completely different symptoms. Not to mention rod knock doesn't go away when the engine warms up.

Thanks for the suggestion, although it would be hard to tell that you spun a bearing by checking the oil, you gotta pull the pan to do that...

 

[DHeath0013]

Has anyone made a discovery as to the root cause of this cold knock issue?

I have a low mileage 1jz and over the past 3 years the cold knocking has gotten a little worse. By worse I mean it will last longer (3 min instead of 1 min) and it has started doing it throughout the year rather than just winter cold starts.

I will be starting it this weekend with the serp. belt removed to prove/dis-prove the tensioner theory.

 

[te72]

Has anyone made a discovery as to the root cause of this cold knock issue?

I will be starting it this weekend with the serp. belt removed to prove/dis-prove the tensioner theory.

Mine was the crappy 3" ebay y-pipe, gotta love crappy flanges.

As for starting it without the serp belt, make sure your battery is in good shape, because you'll be running the engine without the alternator.

 

[Nick M]

Issue: Hearing a slight knocking sound at low rpm, initially on cold startup, goes away when warm or has been warm.

That is usually what people call rod knock, which is really bearing noise from excessive clearance. It can happen to all engines. The symptom is the dead give away.

However, the fact that it goes away after about a minute of running, and usually only happens after it's sat overnight makes me really question that

That is normal for rod knock. The sound goes away because the heat decreases the oil viscosity and it circulates and coats the engine bearings. What you read on SM is often bunk regarding the symptom sound.

 

[Nick M]

If the serpentine belt tensioner is bad, it will make that sound when cold.

Lots of things can knock when cold, and when they heat, the clearance is taken up.

 

[Radial]

Its probably all about clearances becoming bigger.
My impression is that cars in general gets a real nasty treatment in japan...Especially the manual versions of a turbo'd car. Service is not always performed, and cars are "buy and trash" items. A low milage engine is therefore never any guarantee IMO.

My engine has a huge difference when using 5W-30 or 5W-40 oil instead of my usual 10W-50 high performance oil.
The knock is never heard with 5W-30, a tiny 30 sec knock with 5W-40, and about a 1 minute knock with 10W-50 oil.

So viscosity plays a vital role here..... also watch out for valve lifter noise with thick oils.

 

[te72]

Well, considering it had never gotten any worse in the 3 years it was daily driven, weekly abused, I'm not convinced at all that mine was a symptom of any sort of rod knock. Not to mention the oil VOAs never came back with signs of bearing material in it...

Either way, engine is being completely revamped this winter, so if there are any signs to the contrary, I'll be sure to post pics.