Z-Car

Adjusting Valves on a Datsun L-Series engine

Q: I was reading about valve adjustment in my Haynes manual and decided to check mine. I found
out that I have NO clearance! Should I be concerned?

A: You always have to keep the valves adjusted, no matter what cam you have in there! When the valve is closed and the cam lobe is pointing up away from the rocker there should be a clearance between the lash pad surface and the rocker arm tip as specified in the service manual for a stock motor or as specified for the particular cam for a modified motor. If there is no clearance, then the valve is never being allowed to close all the way and hot exhaust gasses are flowing by it all the time. Two bad things happen then, the valve head gets really hot from those exhaust gasses going by all the time, and it never has a chance to pass any of that heat to the coolant via contact with its seat.

This results in the valve getting WAY TOO HOT and it burns just like if you had attacked it with a cutting torch. It happens very quickly to exhaust valves with no clearance, intake valves are cooled once a cycle by the cold air/fuel mixture being inducted by them on the intake stroke, so they can stand this abuse longer.

Fix the situation now, or suffer the consequences. It only costs about $15.0-20.00 to pay a mechanic to adjust the valves this one time (lowest price in Tucson is $56 – Kendel), and then you can learn to do it at your leisure in the next year. Don’t wait longer than that though. Do it at least once a year and check them at every tune up.

Lack of valve clearance will also cause another problem: it will make your car hard to start (or it won’t start) when the engine’s cold, due to low compression. I’ve learned this the HARD way, when everything else seemed to be all right. The original factory book says to check clearances every 6000 miles, but it’s amazing how many NEVER check this. I think that every 6000 is overkill, but every 12000 is a good idea if you want to keep performance up.