A Hydraulic Lash Adjuster or better known as an HLA is nothing more than an ordinary hydraulic lifter. It (on the Mazda KL series engines and the I4 in the base probe) sits directly between the camshaft and the valve stem. As in an old conventional V8 that has pushrods, the HLA simply keeps the space between the camshaft and the valve stem filled 100%. The conventional V8 uses a couple more moving parts, such as pushrods and rockerarms, but the principle/basic function is the same.

Ok, now that you know what an HLA is and what it does lemme explain why they tick.

The HLA’s tick due to crud/gunk/slim buildup in the oil ports that go into the HLA and in the oil ports on the inside of the HLA. Also the HLA tick is caused but crud buildup on and around hte check ball that is located inside the HLA. This check ball simply stops oil from flowing back out of the HLA as the cam turns and puts enough pressure on the HLA for it to open the valve. If the oil gets pushed back out of the HLA because of the check ball not working properly then the next time the camshaft turns the HLA will make a ticking sound. This is the result of the camshaft having space between the lobe of the cam and the upper surface of the HLA, and as the cam turns it comes back in contact/hits the HLA. As you can imagine, to parts of and engine hitting against one another for an extended amount of time is not a good thing. This is one of the reasons why a light weigh oil must be used 10w-30 or 5w-30. Also, a synthetic oil is preferred, as it has alot fewer contamination’s than regular oil. When the HLA’s start to tick you can easily hear them with the engine running at idle and more easily than that they can be heard when the engine is cold and first started.

2) Pull the HLA out of the lifter housing. As seen here using a pair of robogrip pliers.

4) Pull the two (2) halves of the HLA apart.