Understanding Valve Lash

The intake valve is the gateway to the cylinder bore. If the valve lash is excessive, then the valve lift is lost. In turn, intake port flow drops along with engine horsepower and torque. Concerning the exhaust valve, decreased lift limits cylinder evacuation during the exhaust stroke and costs power and longevity due to excessive heat. Also, the incorrect valve lash impacts the valve timing and engine reliability.

If the valve clearance is too tight, the valve will open earlier and close later than intended. If it too loose, the valve will open later and close earlier. The effect of setting the valve lash too tight can result in the valve not fully closing on the seat. This will allow cylinder pressure to escape along with high-temperature combustion gases. It is possible then for the valve head and valve seat’s temperature to become so high that rapid burning can occur.

This has the potential to flame cut the cylinder head beyond the seat and valve face. This is usually further aggravated by the charring of the oil film on the valve stem. This can cause the valve to stick in the guide. If the valve lash is excessive from a lack of adjustment, the engine is noisy, and cylinder fill suffers. Also, there is excessive wear from the valve pounding against its seat.

Adjusting the valves also allows looking things over and spotting potential problems. The state of the lash is telling. A valve that is too tight before adjustment usually indicates valve seat recession or the valve pulling through the cylinder head. In either case, a severe problem is left unaddressed.

In contrast, excessive clearance can reveal a valve stem that is mushrooming or worn parts such as the rocker or adjustment mechanism.

You will find differences on each cylinder, but it should be minimal; the clearance is not too tight or loose compared to the others.

Diesel Exhaust Fluid

The government mandate for clean air has arrived at the farm. The modern diesel engine differs significantly from its predecessors that were devoid of any emissions reduction systems. As of now, all new on-road and more powerful agricultural (100+ hp) engines will have a host of emissions control systems based upon the use of diesel exhaust fluid (DEF).

The two pollutants from the engine’s exhaust that the EPA is concerned with are oxides of nitrogen (NOx) and particulate matter (PM).

DEF is employed to reduce NOx while a diesel particulate filter placed in the exhaust controls PM. When DEF is used on an engine, it is then equipped with a system identified as SCR for Selective Catalytic Reduction. DEF is a mixture of 32.5% automotive grade, very pure urea and 67.5% de-ionized, and very pure water. DEF is produced under strict guidelines identified by the American Petroleum Institute.

DEF allows the engine to function at higher and more optimal combustion temperatures while controlling the NOx as an after-treatment. Most engine manufacturers have concluded that DEF is consumed at the rate of about 3 to 4 percent of the fuel used. Consuming 100 gallons of diesel fuel will use about three to four gallons of DEF.

A sensor measures the amount of NOx and, through a controller, injects or doses the proper DEF amount. Under certain operating conditions, the amount of DEF being dosed will vary. For example, a tractor will use more DEF while pulling a chisel plow than when hooked to an empty grain wagon.

At temperatures below 12 degrees F, DEF will freeze. For this reason, all SCR systems employ an integral heating system and temperature sensor to keep the DEF liquid while the engine is being operated.

DEF labels have a date code, so you know that you are not getting stale and, thus, a less effective product. This is important if you buy DEF in quantity.

If DEF is spilled on the ground, it is environmentally safe (in small quantity) and, when exposed to oxygen, will dry, and leave behind a crystal-like substance.