Valve Clearance – How To Get The Most Out Of Your Engines

Written By:  DLB May 3, 2018 at 7:41 pm

Get The Most Out Of Your Boat Engines With a Few Easy Tips

Our Friends at SCOTT MARINE POWER OF FLORIDA Shared Some Useful Tips On Valve Clearance, Take A Look!


In a marine diesel engine, the load introduced on the engine is usually around 80-90% at cruising speed. If the engine isn’t tuned correctly, you’re not going to get the most out of your engine(s). Proper valve clearance is crucial because it maximizes efficiency and dynamic balancing within the whole engine assembly to provide more power output.  It also helps to extend engine life, increase fuel economy and reduce emissions.


Boat Engines and Valves

What is valve clearance? Valve clearance is the amount of play or looseness in the valve train when the valves are in the relaxed/closed position. Every diesel engine has it’s own unique valve clearance represented in either thousandth of an inch or tenths of a millimeter. The values, for example, might look like this example .010” (ten one-thousandths of an inch)  or .50mm (1/2 of a millimeter). The engine designers must account for the engines’ unique properties when determining the proper clearance.  The valve tappets’ style, camshaft lobe lift, engine speed, valve spring pressure and oil type are some of the determining factors for an engine’s valve clearance.


With a mechanically operated pushrod engine, some clearance needs to be maintained to provide lubrication between valve stem to rocker tip, pushrod cup to rocker arm and tappet to camshaft lobe. If the valve clearance is too tight, then excessive heat builds up leading to increased wear and loss of performance. If the valve clearance is too loose, then the engine won’t get the correct volume of air per event. 


Loose clearance symptoms can be excessive valve train noise, loss of power, excessive white smoke and higher EGT (exhaust gas temperatures).  If the clearance is too tight, then you may get black smoke or burnt valves. In some extreme cases, if the valve clearance is adjusted incorrectly severe engine damage can occur.


Check your engine operators manual to see how often your marine diesel engine requires a valve clearance check and adjustment.


 *article courtesy of Scott Marina Power