Getting your engine’s valve clearance right is a crucial piece of maintenance. If you’re wondering how do you adjust valve clearance on a 6-cylinder engine, you’re in the right place to learn the process.
Proper valve adjustment ensures your engine runs smoothly, efficiently, and powerfully. When the gaps between the camshafts and valves are too tight or too loose, it can lead to poor performance, lost power, and even serious engine damage over time. This guide will walk you through the why and the how, giving you the confidence to tackle this job yourself.
How Do You Adjust Valve Clearance On A 6-Cylinder Engine?
This is the core procedure. While the specifics can vary between engine models, the fundamental principles remain the same. We’ll cover the universal steps first, then discuss common variations you might encounter.
Why Valve Clearance Matters So Much
Engine valves open and close thousands of times a minute. Metal parts expand when they get hot. The clearance, or “lash,” is the precise gap left to account for this thermal expansion.
If the clearance is too tight, the valves won’t fully seal when hot. This causes loss of compression, overheating, and can burn the valve edges. If it’s too loose, you’ll hear a loud tapping noise, the valves won’t open fully, and you lose power and fuel economy.
Tools and Supplies You’ll Need
Gathering the right tools before you start is essential. Here’s a typical list:
- Basic hand tools: wrenches, sockets, and screwdrivers.
- A quality set of feeler gauges.
- A new valve cover gasket (and possibly spark plug tube seals).
- Torque wrench.
- Shop rags and a cleaning solvent.
- A notebook or sheet for recording clearances.
- Your vehicle’s service manual (critical for specifications).
Safety First: Preparing the Engine
Always work on a cool engine. Let it sit overnight or for several hours. Disconnect the negative battery cable to prevent any accidental starts. Remove the engine cover and anything else blocking access to the valve cover, such as intake ducts or ignition coils.
Carefully remove the valve cover itself. You may need to unplug a few electrical connectors. Take your time to avoid damaging the old gasket or the cover itself. Clean any debris from the area before opening it up to keep dirt out of the engine.
Identifying Your Valve Train Type
This is the most important step before adjusting. Look at the top of the valves.
- Overhead Cam (OHC) with Shims: You’ll see a bucket or tappet sitting on top of the valve spring. A small shim sits inside the bucket. Adjustment requires changing these shims.
- Overhead Cam with Rocker Arms: You’ll see a rocker arm pivoting on a shaft or ball, acting on the valve. Adjustment is usually via a locknut and screw.
- Overhead Valve (OHV) with Pushrods: Less common on modern 6-cylinders, you’ll see rocker arms further down. Adjustment is similar to OHC rocker arms.
The General Step-by-Step Adjustment Process
Follow these numbered steps carefully. Refer to your manual for the specific engine firing order and clearance specs (which are often different for intake and exhaust valves).
- Find Top Dead Center (TDC) for Cylinder 1: Rotate the crankshaft slowly using a socket on the crank pulley bolt. Align the timing marks on the pulley and engine block. Confirm the valves for cylinder 1 are “rocking” (one is slightly open, the other closed) or both are fully closed. This means the piston is at the top of its compression stroke.
- Check Clearances: With the engine at TDC for a specific cylinder, you can check the valves for that cylinder. Slide the correct feeler gauge between the cam lobe and the follower (shim) or under the rocker arm. It should have a slight drag. If it’s too loose or too tight, note it down.
- Adjust the Valves:
- For rocker arm systems: Loosen the locknut, turn the adjustment screw to achieve the correct drag on the feeler gauge, then hold the screw and tighten the locknut. Re-check the clearance after tightening.
- For shim-under-bucket systems: This is more complex. You’ll need a special tool to depress the bucket and remove the shim. Then, you calculate the needed shim thickness based on your measurement and the old shim’s size. You must obtain the correct new shim and install it.
- Rotate and Repeat: Following your engine’s specific firing order, rotate the crankshaft to the next position (often 120 degrees for a 6-cylinder). Check and adjust the next set of valves. Continue until all cylinders are done.
- Final Re-check: After adjusting all valves, slowly rotate the engine through two full revolutions. Bring it back to TDC for cylinder 1 and re-check every single clearance one last time to ensure nothing shifted during tightening.
- Reassemble: Clean the valve cover and cylinder head mating surfaces thoroughly. Install the new gasket, reinstall the valve cover, and torque the bolts in the proper sequence. Reconnect all wires, hoses, and the battery.
Common Variations and Pro Tips
Some 6-cylinder engines, like the classic BMW inline-6 or Toyota’s 2JZ, use a shim-over-bucket design. Others, like many older Jeep engines, use simple rockers. Always, always consult the manual.
Here are a few tips that can save you headache:
- Record every measurement before you change anything. This “before” data is invaluable if you get mixed up.
- When rotating the engine, always turn it in the normal direction of rotation (usually clockwise from the front). Never force it backwards against the timing chain tensioner.
- Keep your workspace organized. Use a muffin tin or labeled bags to keep shims or bolts in order.
- If you have a shim system, local auto parts stores often have shim exchange programs, which is much cheaper than buying each one new.
What Happens If You Get It Wrong?
Incorrect adjustment has real consequences. Too tight, and you risk burning a valve, leading to a costly cylinder head repair. Too loose, and the constant hammering can wear out the cam lobes, rocker arms, and valve tips. You’ll also here an annoying ticking sound that gets louder with RPM.
Taking your time and double-checking each valve is far cheaper than an engine rebuild. If you feel unsure at any point, it’s perfectly okay to stop and consult a professional mechanic.
How Often Should You Check Valve Clearance?
This isn’t routine maintenance like an oil change. Check your owner’s manual. Intervals can vary wildly:
- Some modern engines with hydraulic lifters may never need adjustment.
- Many performance engines require check every 30,000 miles.
- Older engines might need it every 15,000 miles or so.
Signs you should check it sooner include a new ticking noise from the engine bay, noticeable loss of power, or poor fuel economy that can’t be explained by other causes.
FAQ Section
What is the valve clearance specification for a 6-cylinder engine?
There is no single spec. It varies by manufacturer, engine model, and whether it’s an intake or exhaust valve. Common ranges are 0.008-0.012 inches for intake and 0.010-0.015 inches for exhaust, but you must find the exact spec for your engine.
Can I adjust valves on a hot engine?
Some older engines specify “hot” adjustments. However, for most DIYers, adjusting a cold engine is safer, more comfortable, and is the spec given for most modern vehicles. Always follow your manual’s instruction on hot vs. cold.
How long does it take to adjust valves on a 6-cylinder?
For a first-timer, budget 3-6 hours depending on your engine type. Shim-and-bucket systems take significantly longer than rocker arm systems. With experience, you can cut that time in half.
What’s the cost if a shop does it?
Shop rates vary, but for a 6-cylinder engine, expect to pay between $300 and $800. The higher end is for shim-type adjustments due to the extra labor and parts cost.
Is adjusting valve clearance the same as a “valve job”?
No, not at all. A valve adjustment just sets the gap. A valve job is a major overhaul where the cylinder head is removed, and the valves and their seats are machined or replaced to restore compression and sealing.
Adjusting your own valve clearance is a satisfying and money-saving project. It requires patience and attention to detail, but it’s very achievable with the right guidance. By following these steps, using your service manual, and working methodically, you can ensure your 6-cylinder engine runs at its best for many more miles to come. Remember that the key is understanding your specific engine’s design before you start turning wrenches.