M8 Adjustable Rocker Arms

Harley’s four valve head has two rocker arms that control two valves each. One rocker arm controls a pair of intake valves and one arm controls a pair of exhaust valves. The valve tip heights are exactly the same when issued from the factory.

Eventually (usually over 50k miles), parts begin to wear. The valve face, valve seat, the tip of the rocker arm, and the tip of the valve face will all establish varying degrees of wear. When this occurs, there is eventually a .010″ to .015″ difference in valve tip heights. This is the measurement of the length of valve stem that protrudes from the valve guide. This may sound like a small measurement, but when it comes to the valve train of a motor, this difference is huge. The result is a noisy and less efficient motor.

The repair for this condition does not have to be a major expense. Harley now has Screamin’ Eagle adjustable rocker arms. These adjustable rocker arms allow for a compensation adjustment for the valve that has more wear. By simply setting the adjuster to zero lash on the loose valve, the wear factor is compensated and the valve train moves like new again. Anyone who is familiar with metric motorcycles may already be familiar with this type of adjustment.

On most metric bikes, new and old, valve adjustment is part of a major service. Fortunately, these motorcycles have access covers that allow you to make the adjustments without any disassembly of the motor.

If rebuilding the top end of your Milwaukee Eight, we suggest measurement of valve tip heights and installation of adjustable rocker arms. Aftermarket companies like Jims Tools will also be selling these arms. Choose what works best for your budget.

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