Yamaha YBR 125 workshop manuals on Ebay UK
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Safety Message: Top-end disassembly involves handling sharp metal edges and pressurized springs. Wear eye protection to guard against debris and ensure the engine is completely cold before starting. Use a dedicated parts tray to organize bolts and avoid dropping small components (like dowels or circlips) into the crankcase. If the cylinder head is seized, do not pry against the gasket surfaces with a screwdriver, as this will cause permanent oil leaks.
Removing the cylinder head and barrel (cylinder) is the first major step for any YBR 125 engine refresh. Whether you are addressing blue smoke (valve stem seals), low compression (piston rings), or a blown head gasket, this 2026 guide ensures you get the "top end" off safely without damaging the delicate mating surfaces.
1. Essential Tools & Replacement Parts
Having these items ready before you pull the head will save hours of downtime. eBay remains the best source for these specific 125cc components:
Yamaha YBR 125 Top End Gasket Sets Valve Spring Compressor Tools T-Handle Socket Sets (8mm, 10mm, 12mm)
2. Pre-Removal Checklist
Drain the Oil: Prevent a mess when the cylinder barrel is lifted away from the crankcase.
Remove the Exhaust & Intake: Disconnect the exhaust header and either the carburetor or the EFI throttle body.
Set to TDC (Top Dead Center): Rotate the flywheel until the 'T' mark aligns with the pointer. This ensures the valves are closed and tension is off the camshaft.
3. Step-by-Step Removal
The Cam Sprocket: Remove the cam chain tensioner first (on the back of the cylinder). Then, unbolt the cam sprocket. Use a piece of wire to "hook" the chain so it doesn't fall into the bottom of the engine.
The Head Bolts: There are four main M8 studs and two smaller M6 bolts on the side. Loosen the main studs in a star pattern (half-turn at a time) to prevent the head from warping.
The Cylinder Head: Lift the head straight up. If it is stuck, tap it gently with a rubber mallet. Do not use a metal hammer.
The Cylinder Barrel: Once the head is off, slide the barrel up the studs. Be ready to catch the piston as it clears the bottom of the cylinder so it doesn't slap against the crankcase.
4. The "Hidden" Danger: Locating Dowels
There are small hollow metal "dowels" between the head and the barrel, and between the barrel and the crankcase. These often fall out during removal. If you lose one, the head will not align correctly, leading to oil leaks or cam chain wear. Always check they are present before reassembly.
5. 2026 Pro-Tip: Piston Pin Inspection
While the top end is off, check the "small end" bearing (where the pin goes through the connecting rod). If there is any noticeable "up and down" play, your engine requires a bottom-end rebuild as well. Sideways play is normal; vertical play is a sign of imminent failure.
use a soft mallet .
job done and very easy to do
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