Here's a general overview; specifics will vary slightly depending on the engine (2.5L or 4.0L):
1. Preparation:
* Consult your repair manual: A factory service manual specific to your 1988 Jeep Comanche is crucial. It will provide precise specifications for valve clearances (lash), the firing order, and the detailed procedure for your specific engine. Online manuals are available, but a printed copy is often easier to use.
* Gather tools: You'll need a socket set (including metric sizes), wrenches, valve adjusting tools (feelers gauges), a torque wrench, jack stands, a crankshaft locking tool (essential to prevent engine damage), and potentially a compression tester (to check engine health before and after the valve adjustment).
* Safety first: Disconnect the negative battery terminal. Work in a well-ventilated area.
2. Accessing the Valves:
* Remove the valve cover: This usually involves removing various components, such as air cleaner, possibly some hoses, and possibly the distributor cap. The process is detailed in your repair manual.
* Locate the rocker arms and pushrods: Familiarize yourself with their location and function.
3. Setting Valve Lash (Clearance):
* Engine at Top Dead Center (TDC): Use the crankshaft locking tool to precisely position the engine at the top dead center (TDC) of the appropriate cylinder for the valve you're adjusting. Your repair manual will explain how to do this correctly for each cylinder, based on the firing order. Getting this wrong is the most common mistake and can lead to bent valves.
* Measure Valve Lash: Use feeler gauges to check the clearance between the rocker arm and valve stem.
* Adjust Valve Lash: Most likely you will have to loosen the rocker arm nut, adjust the push rod (if applicable), and then tighten the nut to achieve the correct clearance specified in your repair manual. The repair manual will show how the adjustment is made—some engines require shims, others allow direct adjustment via the pushrods.
* Repeat: Repeat this process for all valves, ensuring the engine is at TDC for the correct cylinder each time.
4. Reassembly:
* Replace the valve cover: Tighten the valve cover bolts to the torque specifications listed in your repair manual.
* Reconnect everything: Reinstall any components removed earlier.
* Reconnect the battery: Reconnect the negative battery terminal.
5. Verification:
* Start the engine: Listen for any unusual noises.
* Check for leaks: Inspect for any oil leaks around the valve cover.
* Consider a compression test: After valve adjustment, a compression test can ensure the valves are properly adjusted and the engine is healthy.
Important Considerations:
* Hydraulic vs. Mechanical Lifters: The type of lifters in your engine (hydraulic or mechanical) will influence the valve adjustment procedure. Hydraulic lifters typically self-adjust, while mechanical lifters require manual adjustment. Your repair manual will clearly state which type you have.
* Engine Temperature: The engine should be at operating temperature (if your repair manual doesn't specify otherwise) for the most accurate adjustment, to account for thermal expansion. This is because the clearances will change as the engine warms up.
* Torque Specifications: Always use a torque wrench and adhere to the manufacturer's torque specifications found in your repair manual. Over-tightening can cause damage.
This is a simplified overview. Always consult your specific 1988 Jeep Comanche repair manual for detailed instructions and specifications. Attempting this repair without the manual is strongly discouraged. If you lack the experience or tools, seeking professional help is the safest and best course of action.
