Yamaha YBR 125 workshop manuals on Ebay UK
One of the most critical checks you can perform on a Yamaha YBR 125—especially after a rebuild, a long period of storage, or a clutch change—is the Oil Flow Test. Because the YBR 125 does not have an oil pressure gauge or a "low oil" dashboard light, a failing pump or a blocked gallery can destroy your cylinder head in minutes without any warning.
1. Essential Parts & Replacements
If you suspect an oil delivery issue or are performing a preventative refresh during a rebuild, these parts are essential:
New Yamaha YBR 125 High-Flow Oil Pumps – Replace immediately if the plastic drive gear shows any signs of wear or "pitting."Right-Hand Crankcase Gaskets – You must remove the clutch cover to access the pump and the centrifugal filter.Magnetic Oil Drain Plugs – A great way to catch metal shavings before they reach the pump screen.
2. How to Perform the "Bleed" Test
This simple test confirms that oil is actually reaching the top end of the engine. It should be done every time you change the oil or remove the right-side engine cover.
Locate the oil gallery check bolt on the cylinder head (usually a small 8mm bolt on the right side of the head, near the spark plug).
Start the engine and let it idle.
Slowly loosen the bolt (do not remove it completely).
The Result: Within 5–15 seconds, oil should begin to "weep" or seep from the threads.
If no oil appears after 20 seconds, kill the engine immediately.
3. Why Oil Fails to Circulate
The Centrifugal Filter: If this internal filter (located on the crank) is clogged with sludge, it acts like a "cork." Clean it every 6,000 miles to ensure the oil can actually flow toward the pump.
The Sump Strainer: Check the wire mesh strainer behind the 19mm drain plug. If this is clogged with gasket sealer or metal bits, the pump will starve.
Pump Priming: After a rebuild, the pump can occasionally have an air lock. Ensure you pre-fill the oil pump with fresh oil before bolting it in.
4. 2026 Warning for High-Mileage Bikes
As these bikes age, the plastic drive gear on the oil pump can become brittle. If you are doing a clutch replacement, it is worth spending the extra few pounds to replace the pump assembly entirely. It is cheap insurance against an engine seizure.
I am having a lot of engines in seized and i am not sure why , maybe bad oil maybe old thin oil .maybe running oil to low for pump to circulate , maybe i do not know !! .
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