Questions and Answers
A Tapping Nissan Truck
Q. I have a question for you if you have a spare second. I have a 1991 Nissan pickup truck Manual 2WD 2.4L SOHC 12 valve (2 intake 1 exhaust) engine with 174,000 miles on it. After it warms up, the idle starts to get rough and there sounds like there is a lot of noise coming from the valve train. (It's ok when it just starts and is cool) The noise goes away when the RPM's come up. My best guess is that the cam followers/rocker arm setup is getting worn. I took off the valve cover to find that there is no adjustment for the valves. (As it explains on the emissions sticker under the hood) Unfortunately the Haynes Manual for this model year doesn't include anything about this version of engine (actually it is lacking a lot of information about the whole truck)
I have replaced most of the critical tune up parts for a vehicle of this age, to try to fix the rough idle. While other squeaks and rattles disappeared this one still persists. What can I do to adjust the valves, or do I just need to replace the cam followers on the rockers? I'm not familiar with the maintenance of non-adjustable overhead valve train configurations. Any insights you can give would be greatly appreciated.
Thank you.
Matt
A. There could be a number of reasons for this. It's possible that the oil pump is not supplying enough pressure at idle to keep the lifters pumped up. I would recommend an oil pressure test with an external gauge to check this.
Another possibility is the lifters themselves are wearing out and not holding the oil to keep them pumped up.As far as engine wear goes, I would take the valve cover off and look at the cam lobes very closely. See if there is a grove where the rockers rides on the lobes. If there is a significant groove, then the cam needs to be replaced, along with the rockers. If the cam is in good shape, then the wear is in the rockers. Take one off and look at where it rides on the cam. It should have a smooth curve to it. If there is a flat spot, then replace them. Since the lifters and the rockers are one unit, a lot can be eliminated by replacing the rocker arms.
Before I went looking at a more expensive repair, you can try cleaning the engine as I describe in a Tapping Maxima and see if that helps any. If not, then you will need to dig in a little deeper.
