Engine knock, only when warm and at idle?

[Skid]

Originally Posted By: JZA70
I'm honestly leaning towards a lifter issue as this motor uses hydraulic lifters and because the knock noise is very intermittent.


I think that a JZ engine has bucket/shim lifters (not hydraulic). Thicker oil will help if it is a rod knock (rod knock is worse when warm/hot since the oil is thinner when hot). However, other things can cause knocking like loose pulleys, loose flywheel, etc. I would park the car until it's sorted out. Hopefully, a car that old isn't your daily driver.

BTW, I have a '91 Supra with a 7MGTE (I have a BMW and a Scion as well). Man, maintenance intensive (the Supra, that is). Constantly changing hoses, etc.

 

[JZA70]

You're right Skid, I was under the impression that I had hydraulic lifters. I understand that other things can cause knock, but the big thing to remember here is that it ONLY makes the noise when it's warm. I think that eliminates a lot of the other potentials such as a bad tensioner or pulley and other things that wouldn't be temperature sensitive like oil/bearing clearances would be.

The car is my daily driver. What's sad is that it was just purchased from a dealer in Japan and shipped over to me. It came with this issue but no one ever said anything, though I'm honestly not really surprised, it was a dealership after all.

I had an 89 turbo/targa MA70. Besides blowing almost every coolant hose in the bay, it was a pretty reliable fun car. This is the first JZ motor that I have owned with this issue. It must have been really neglected/abused because as I'm sure you know, it takes a lot to destroy one of these motors.

 

[Trav]

I would start by removing the accessory belts and trying it, probably not going to help but at least you can eliminate a bad A/C compressor.
My next step would be oil pressure test and using a stethoscope to pinpoint the noise then pulling the valve cover and examining the lobes and buckets and make sure the adjustment is within specs.

 

[flacoman]

+1 on verifying oil pressure.

 

[JZA70]

So a quick update, I unplugged each injector one a time and the noise did NOT go away, it stayed the exact same through all six cylinders. I talked to a local mechanic and he said believes the noise is coming from the head, but doesn't have any idea where. The noise is coming from the front of the engine, so I'm going to take off the valve covers and see if I can find anything abnormal.

 

[Lubener]

I would connect a mechanical oil pressure gauge and see what is happening.

 

[Trav]

I suspect either a front cam bearing (there is none, its the head casting itself with a cap AFAIK) a bad lobe or less likely a bad bucket or worn shim.
Have him use some plastigauge on the cam holders. I have heard this before years ago on a 4 cyl something or anther i don't remember what make it was.

The aluminum head expands more than the iron/steel shaft when warm/hot and the clearances increase.

 

[OVERKILL]

Originally Posted By: JZA70
So a quick update, I unplugged each injector one a time and the noise did NOT go away, it stayed the exact same through all six cylinders. I talked to a local mechanic and he said believes the noise is coming from the head, but doesn't have any idea where. The noise is coming from the front of the engine, so I'm going to take off the valve covers and see if I can find anything abnormal.


Great to hear. I would head Trav's advice at this point as this is indeed likely valvetrain related.

 

[ltslimjim]

^Ditto. So, maybe he caught this early and a simple cam replacement does the trick?

 

[Trav]

If that is the problem a good mechanic will be able to figure out pretty quick if its the head, the cam or both.
Plasigauge is a quick and dirty way of getting a rough idea if something is really out of spec but in general i wouldn't assemble an engine with it.
If its showing excess clearance then cam removal then using a dial indicator or inside mic on the bearing bores and outside mic on the cam will give you the exact clearance.

On long engines like a straight 6 with aluminum head another problem can be bulging in the middle of the head from heat causing excess run out, they will check this also.
Basically if it determined the noise is from the head then it usually involves pulling the head and doing some serious parts inspection and measuring tool work.

Problems like this and painting are my favorite types of work, i wish i could get at it. LOL