* Worn or Damaged Lifters: Hydraulic lifters (if equipped) are the most common cause. Under load, oil pressure might be insufficient to keep them properly inflated, leading to a tapping sound. Fast idle increases the demands on the lifters. Worn lifter bodies or sticking internal components contribute to this.
* Worn Camshaft Lobes: If the camshaft lobes are worn, they won't properly actuate the lifters, resulting in noise. This usually presents as a consistent, rhythmic tapping.
* Worn Rocker Arms: Similar to lifters, worn rocker arms can lose their proper contact with the valves, leading to noise. This is more likely to manifest as a clicking or ticking sound.
* Low Oil Pressure: Insufficient oil pressure can affect the entire valve train. Check your oil pressure gauge. Low pressure can be caused by a failing oil pump, clogged oil passages, or low oil level.
* Loose Rocker Arm Adjustment (If equipped with adjustable rockers): If your Bronco II has adjustable rocker arms, they might be incorrectly adjusted. Too much or too little clearance will cause noise.
* Valve Lash (If equipped with solid lifters): Some older engines used solid lifters requiring periodic adjustment of valve lash. Improper lash can cause a rattle. This is less likely on an '87 Bronco II, but possible depending on the engine.
Troubleshooting Steps:
1. Check the Oil Level and Pressure: This is the *first* thing to do. Low oil is a major culprit.
2. Listen Carefully to the Noise: Try to pinpoint the location of the noise. This can help narrow down the possibilities.
3. Inspect the Valve Cover: If possible, remove the valve cover (after engine cool-down) to visually inspect the lifters and rocker arms for damage or wear.
4. Oil Change with High-Quality Oil: A fresh oil change with the correct viscosity (consult your owner's manual) might temporarily alleviate the problem if it's due to dirty oil or low oil pressure.
5. Professional Diagnosis: If you're not comfortable with engine work, a mechanic should inspect the engine and perform a proper diagnosis. This will save you time and potentially money in the long run.
Ignoring a valve train rattle can lead to serious engine damage. Don't delay addressing this issue.
