Valve adjustment outside our company is the most overlooked yearly maintenance task most people dont even know needs doing!!
Inside your small engine, there are valves. most people know that valves open and close and pistons go up and down sucking in fuel, closing valves, compressing that mixture and then BOOM!! A spark inside a small chamber filed with compressed air and gas erupts! That explosive force "and heat" throws the piston downwards and spins the blade and in come cases turns self propelled systems transmissions and electricity generators and many more tasks!
Get to the point of valve adjustments and how they relate to a yearly adjustment!
Oh, yeah! So yes, the valves inside the chamber become hot. They expand!
The item that keeps the valve height constant on small engines is usually a solid lifter that requires periodic manual adjustmentbecuase of wear in the engine those tolerances can change. Unless your engine says "Hydraulic valve lifters" you probably have solid lifters that require checking and possible adjustment. Here is another drawing to help you understand how the space inside is adjustable.
As part of our service, we take off each and every valve cover and perform a FREE valve lash check. For a push mower, if the adjustment is needed, add $15 and for a rider add $25 commercial $30-$35. You dont know how many times we perform this free checking where the va was not required at a great sacrifice in time. It is the equivalent of going to the doc. They test you included in the original charge, but to fix you, if something is wrong, the medicine costs!
You mentioned ENGINE FAILURE Tom, What's up with that? When your small engine first leaves the factory, the engine is perfectly aligned. Over time, as you spend more time in the yard cutting grass, the moving parts within the engine will settle into slightly different patterns. This resettling is normal, but also means that parts like valves need to be realigned periodically.
Once your valves start to lose their proper clearance, they'll be easy to notice. Your mower may have a rough time idling, especially before it has time to warm up. This rough idling is caused by the valve opening late, choking off fuel. Stalling after a cold start is common. In other cases, you may hear a loud rattling noise as the valve knocks against the side of the shaft. Since some symptoms often disappear after the car warms up, they're easier to ignore. But ignoring these warning signs may end up costing you more through lost performance and stress from warning letters from the HOA or a visit from the dreaded code enforcement.
Too much clearance causes a rattling sound and lackluster acceleration. Mowing with too much clearance leads to less overall damage than mowing with tight clearance. But, it should still be taken care of quickly before the mowing performance lacks.
Running with the valves too tight causes the most damage. In severe cases, your engine may overheat and burn out a valve, which is a much more costly repair. If you notice these warning signs and don't take care of them you will almost certainly regret it. Stick to your maintenance schedule and have your valves adjusted as needed.