How to adjust the valve clearance of a 4JB1 engine?
3 Answers
Rotate the flywheel until the two rocker arms of the cylinder to be adjusted open and then just close the valve, with the two rocker arms parallel. Turn the flywheel slightly in its original direction (to prevent the cam from pushing the push rod) to adjust the valve clearance, because the valve opens once every two rotations of the flywheel, and the cam will not push the push rod.
Adjusting the valve clearance on a 4JB1 engine requires careful operation. I've done it multiple times myself, and the engine must be cold before starting—thermal expansion can affect precision. First, prepare the tools: a set of feeler gauges, the appropriate wrenches, and a crankshaft turning tool. Rotate the crankshaft to the top dead center (TDC) position of the first cylinder's compression stroke—this is a critical step, as getting the sequence wrong may cause engine vibration. Adjust the intake valve clearance to 0.25 mm and the exhaust valve to 0.40 mm. Gently slide the feeler gauge between the valve stem and rocker arm; it should have slight resistance but still be movable. Loosen the lock nut, adjust the screw position, then retighten and recheck the clearance. Take your time—work on one cylinder at a time. After finishing, start the engine to test for smooth, quiet operation; otherwise, rework might be needed. Beginners should practice on simpler models first or seek help from a friend to ensure safety and avoid mistakes.
During my DIY project, I learned how to adjust the valve clearance on a 4JB1 engine: First, ensure the engine is completely cold, typically after sitting for several hours. Then, rotate the crankshaft to position the first cylinder at top dead center on the compression stroke. According to the manual, set the intake valve clearance to 0.25mm and the exhaust to 0.40mm. Use a feeler gauge to adjust the valve clearance by slowly turning the adjustment screw until the gauge is snug but can still be pulled out—avoid over-tightening or leaving it too loose. After tightening the locknut, always recheck the clearance. Once completed, start the engine; if the ticking noise reduces, the adjustment is successful. If unsure about the clearance values, refer to the factory manual or online tutorial videos. This DIY process can save on repair shop costs, but it's crucial to learn the basics beforehand to avoid damaging components. Beginners are advised to record each step for reference. With practice, efficiency and confidence will naturally improve.
