Yamaha YBR 125 blog valve clearance adjustment tappets

• Yamaha YBR 125 for sale on Ebay UK 

  Yamaha YBR 125 parts for sale on Ebay UK

Yamaha YBR 125 workshop manuals on Ebay UK

Just done a tappets adjustment on and engine i have removed , ill be fitting the engine soon so ill take some photos of this as i go along .

this is a very easy job with engine out or in .

make sure you change the o-rings you might get away with it but more often than not no and oil will leak
especially around the cam sprocket cover and drip onto exhaust causing excess smoke .

Back in 2014, I wrote about the importance of the 0.10mm "sweet spot." Ten years later, this remains the single most important bit of "R&D" you can do for your YBR 125’s engine. A well-adjusted top end ensures your "Income Fortress" stays fuel-efficient and easy to start in the winter.

1. The 2026 Toolkit

To do this right, you need more than just a spanner. You need the "Margin of Safety" that correct tools provide:

• Feeler Gauges: You need a high-quality set that includes 0.10mm and 0.12mm.

• Tappet Tool: While you can use pliers, a dedicated square-headed tappet wrench is a "Must-Buy" to prevent rounding off the adjuster screw.

• 17mm Socket: To rotate the crankshaft via the timing hole.

2. Finding Top Dead Centre (TDC)

1. Remove the two plastic timing bungs on the left-hand engine cover.

2. Rotate the engine anti-clockwise until the "T" mark aligns with the pointer.

3. The Wiggle Test: Grab the rocker arms. If they don't move at all, you are on the wrong stroke. Rotate another 360 degrees until both arms have a tiny bit of "play."

3. The "Drag" Technique

• Intake: Set to 0.10mm.

• Exhaust: Set to 0.12mm (slightly wider for better heat "Resilience" with modern E10 fuel).

• The Feel: Slide the gauge in. It should feel like a piece of silk being pulled through a book—firm but not stuck. If the gauge is "grinding" or you have to force it, it's too tight.

4. Common 2026 Mistakes

• Overtightening the Locknut: It only needs about 7Nm-10Nm. If you "Aggressively" tighten it, you’ll stretch the threads, causing the clearance to change or the bolt to snap.

• Skipping the Re-Check: Always rotate the engine two full turns and re-measure. Often, tightening the locknut pulls the adjuster slightly, changing your perfect 0.10mm to a 0.08mm.

The Verdict:

If your bike sounds like a sewing machine, you’ve done it right. A "happy valve is a tappy valve"—silent valves are usually too tight and will eventually burn out, leading to a costly "Maintenance Debt."

                             remove inspection covers ( 24mm)

change all O-rings 

     remove plastic inspection covers use a good fitting tool to avoid                                              damage to them.

                            remove camshaft sprocket cover

       change this O-ring otherwise this leaks directly onto exhaust

                            turn engine over anti clockwise with crank nut ( 17mm)

 make sure piston is at top dead centre and marks are aligned on the
 sprocket ( white marks ) i have painted them white but manufacturer markings are easy to see

 

make sure lower marks are aligned buy viewing in inspection window

then make sure you have free play in both rocker arm 

to ensure you are a TDC on compression stroke (valves closed )

                         check clearance gap is with above specs

                                  adjust where necessary

easy now just check every thing is tightened to specs and turn engine over a couple of times 

make sure things go smooth and fit inspection covers changing orings .

                           

see more Yamaha YBR 125 blog posts