Proper Valve Adjustment on Yamaha R6 and YZ250F Motorcycles

Understanding Valve Adjustments on the Yamaha R6

Proper valve clearance is critical to engine performance and longevity on any motorcycle, especially high-revving sportbikes like the Yamaha YZF-R6. Adjusting the valves on your R6 involves measuring the clearance between the valve stem and the rocker arm and shim stack, and adjusting as needed by changing shims. This ensures optimum valve seating, timing and lift.

Why Valve Adjustments Are Needed

During normal engine operation, valve components wear over time. This can lead to looser tolerances between the valves and valve seats, resulting in improper sealing, noisy operation, loss of power, and increased emissions. Periodic valve adjustments are needed to account for this wear and maintain proper clearances.

Yamaha recommends checking valve clearances every 16,000 miles for the R6. More frequent adjustments may be needed for bikes subjected to heavy use, such as on the racetrack. Always consult your owner's manual for the proper service intervals.

What You Need for the Job

Doing a valve adjustment on your R6 requires some specialized tools and supplies:

• A service manual specific to your bike model and year
• Feeler gauges
• Flat bladed screwdriver
• Allen wrenches
• Replacement shims
• Torque wrench

The service manual is critical, as it will provide the proper clearances and procedures. Make sure you have a full set of shims in incremental sizes to swap in as needed during the adjustments.

Step-by-Step Valve Adjustment Procedure

Here is an overview of the valve adjustment process on the R6:

1. Remove upper fairings and fuel tank for access. Consult service manual for details.
2. Remove valve cover and gasket.
3. Rotate engine to Top Dead Center (TDC) on the compression stroke for cylinder being adjusted. The service manual will explain how to find TDC.
4. Check clearances with feeler gauges and record measurements.
5. If adjustment is needed, loosen the lock nut and turn adjuster bolt until proper clearance is achieved.
6. Hold adjuster bolt in place and retighten lock nut.
7. Repeat process for remaining cylinders.
8. Reinstall valve cover using new gasket, torque bolts to spec.
9. Reinstall remaining components.

Setting Proper Clearances

The service manual will provide the correct valve clearance for both intake and exhaust valves. This spec must be followed precisely. Typical values are around 0.10mm to 0.20mm for cold settings. Narrower clearances are used at higher RPMs to account for expansion.

Always set the clearances with the engine completely cooled to room temperature. Measure each valve individually by sliding the appropriate feeler gauge between the bucket and valve stem. Start with the smallest gauge that fits and work up to find the ideal fit based on the spec.

Removing and Installing Shims

To adjust a valve that is too tight or too loose, you'll need to swap in a different shim. Removing shims requires a magnet to extract them from the recess in the bucket. Install new shims of the required thickness carefully, making sure they seat properly.

Shims are available in increments ranging from 1.20mm to 2.20mm generally. Have a full range on hand so you can dial in the perfect fit. Don't stack multiple shims together - use the single shim that gets you to the proper clearance.

Special Considerations

Here are some special things to keep in mind when adjusting R6 valves:

• Use a torque wrench for all fasteners and torque to spec.
• Make sure the cotter pin is installed securely on the adjuster bolt after tightening the lock nut.
• Check clearances when the engine is cold.
• Work carefully to avoid dropping shims or parts into the engine.
• Adjust valves in the proper firing order (1-2-4-3 on the R6).
• Check valve lash every couple of races if used on a track.

Conclusion

Regular valve adjustments are crucial on high-performance engines like the R6 to maintain power and reliability. While it requires some specialized tools and knowledge, it can be done by the home mechanic with patience and care. Always follow the procedures in your factory service manual exactly. Proper valve clearances will keep your R6 running smoothly for miles to come.

Tips for Proper Valve Adjustment on the YZ250F

Keeping accurate valve lash is critical on high-performance dirt bikes like the Yamaha YZ250F. Valves must seat properly against the cylinder head to ensure good compression and prevent engine damage. Here are some key tips for setting valve clearances correctly on the YZ250F.

Consult Your Service Manual

Always follow the specifications and procedures outlined in the factory service manual for your bike's model year. Valve adjustment settings and procedures can vary across model years so make sure you have the correct info.

Check Clearances When Cold

Cylinder head temperature affects valve train measurements. Always check clearances with the engine completely cooled off to room temperature. Checking lash on a hot engine will result in inaccurate adjustments.

Work In a Clean Area

Make sure you work in a clean, well-lit workspace when doing valve adjustments. Dirt in the engine can cause rapid wear. Dropping adjustment components or shims into the cylinder can be detrimental.

Use Feeler Gauges

Good quality feeler gauges are a must for accurately setting valve lash. Make sure the blade can access the tight space between the bucket and valve stem. Blades made from flexible materials make this easier in tight confines.

Adjust in Proper Firing Order

Loosen the locknut and adjust valves in the cylinder's proper firing order, which is 1-3-2-4 on the YZ250F. This ensures proper TDC positioning and accuracy. Follow each cylinder through the complete adjustment before moving to the next.

Don't Over-Tighten Locknuts

It doesn't take much torque on the adjuster locknut to hold the setting. Over-tightening can damage threads and lead to improper adjustments. Finger tighten plus 1/4 turn with a wrench is sufficient.

Check Your Work

Always double check clearances after tightening the locknut before moving to the next cylinder. Make sure the adjustment hasn't changed as you tightened the nut.

Recheck After Reassembly

It's wise to recheck valve lash on each cylinder again after reinstalling camshafts, covers, etc. The cylinder head can shift slightly during reassembly, throwing off your carefully adjusted settings.

Look for Wear

Inspect valve train components closely during adjustment procedures. Look for excessive wear, overheating or damage which could indicate larger underlying issues that need to be addressed.

Conclusion

Proper valve adjustment is not difficult on the YZ250F but it does require special tools, patience and care. Following the factory procedures exactly along with these tips will help you nail perfect valve lash every time, keeping your engine running strong.

FAQs

How often should I check valve clearance on my R6?

Yamaha recommends checking valve clearance every 16,000 miles. However, more frequent checks may be needed if the bike is subjected to heavy use like track days.

What tools do I need to adjust Yamaha valves?

You'll need feeler gauges, Allen wrenches, a torque wrench, replacement shims, a flat blade screwdriver, and a service manual specific to your bike model and year.

Should valves be adjusted on a hot or cold engine?

Always adjust valve clearance with the engine completely cooled off to room temperature. Hot measurements will be inaccurate.

What can happen if I don't adjust my valves properly?

Improper valve clearance can lead to poor compression, loss of power, increased emissions, engine noise, and eventual valve or valve seat damage.

How tight should I torque the adjuster locknut on my YZ250F?

Finger tighten the locknut, then add just 1/4 turn with a wrench. Over-tightening can damage threads and components.