Upper Engine Camshaft rattling and knocking

Hello all my name is: JDM Joe

I have a: (1991 GTO GTO - Z16A 1991 6G72 MNPM

GTO, 5FM/T 3000 / 4WD / 4WS Modification: Z16A Classification: MNPM Production: 01.09.1990 - 03.08.2000

It has the following issue: There is rattling in the upper engine. We have been unable to directly isolate the problem.
At first we thought it may be dry and so made sure all pumps, oil and fluids had good contact.
The engine is well lubricated.

We think it could be the following:

  • Camshaft is not aligned properly
  • Camshaft is bent, damaged (off a few degrees)
  • timing belt/cog is off by a few clicks
  • Camshaft seal or pins may not be fitted well enough.

We are going to put jack the car up and turn the engine by hand. This requires one to turn the engine by hand and the other to record the cams rotating motion with a video.

Has anyone else had such an issue with unhealthy rattling in the upper engine?

We would like to rule out any other possible causes before we commit to buying new camshafts.

Any advice is much welcomed!!!


So, after turning the engine by hand, there is no unnatural contact on the journals and all the rockers/springs are firing in sequence.

On closer inspection, there is now a lot of slack on the belts and the belt/crank for the upper engine seem off by a couple of clicks.


This is good news as it means I probably won’t need new camshafts installing. I will be sure to replace the lifters with the 3rd generation ones after the belts are done.

When we removed the wheel and arches, we noticed the wishbone and rods are completely gone. No surprises there. It will likely need some welding done to it.

Could just be lifters?

Couldn’t rule it out completely. The lifters seem to be in good order as they were serviced by the previous owner. I should probably link a video so that the sound can be heard. It sounds like more of a metal grinding sound than a consistent knocking sound.

I don’t want to keep firing her up until I have fixed it.