Ever started up your car and discovered an annoying tapping sound coming from your beloved engine? It’s a fairly common problem for cars of a certain age or mileage that have been mildly neglected in terms of servicing and general maintenance. Known as a ‘tappety’ engine, what causes this frustrating and potentially destructive noise?
There can be slight confusion in the car world about the definition of tappets. You may hear people referring to the annoying ticking noise as ‘engine tappets’. This is slightly incorrect, as the noise can be down to a multitude of components within an engine’s valvetrain. However, a tappet (also known as a cam follower or lifter) is a small cylindrical mechanism which is attached to the end of the pushrod (in overhead valve engines) or the rocker arm (in overhead cam engines).
So although the tapping sound coming from the engine’s head may in fact be a problem with the tappets specifically, it could also be a problem with the camshaft, rocker arms, valves or even just a lubrication problem.
As stated above, a tappet sits on the end of pushrod or rocker arm and the other end interacts with the lobes of the crankshaft, initiating the motion of the valve to open and close as the cam profile rotates around its own axis. Since the tappets ‘lift’ the rocker arm on a OHC engine, they have grown the nickname ‘lifters’. A locking screw is located at the connection to the rocker arm which can increase or decrease the amount of lift that the tappet allows from the camshaft, thus making the amount of valve lift adjustable through this method.
Over time, as engine oil starts to gather dirt and increase in viscosity, the interaction between the camshaft and tappets begins to wear down both components to a point where an audible noise can be heard between them as the camshaft spins and the lobes lift and then drop the tappets. A lack of lubrication can also affect the rest of the valvetrain in the same way, with rocker arms, pushrods and valves clanging around the engine due to oil starvation.
Not only can this degradation lead to an annoying tapping noise but it can also decrease engine efficiency, and therefore power. A worn down camshaft or tappet will result in a valve not opening to its pre-set lift distance, restricting the air/fuel mixture that’s trying to rush into the cylinders. In extreme cases where this problem has been neglected for many thousands of miles, the lack of lubrication could lead to expensive damage to the components within the valvetrain, with the camshaft being the priciest part to damage.
Another source of a tappety engine is badly-adjusted tappets. The rattle from the engine is generally down to excessively-spaced tappets, as the tappet stops having continual contact with either the pushrod/rocker arm and the camshaft. Once the engine is warmed up, the valve stem thermally expands therefore spacing is needed to accommodate this expansion. This is the reason why valve adjustment should be completed when the engine is as cold as possible. On the other hand, if the tappet adjustment is too tight, the valves can stay open slightly too long, meaning much more heat is transferred through to it than it’s designed to handle which can cause chips and cracks in the valve.
Checking the viscosity of the oil should be the first port of call, as this could potentially be the easiest fix. If the wrong oil has been used within your car, the lubrication of the many moving parts within the valvetrain will be altered from the conditions that the components are designed for. A more and less-viscous oil than necessary would lead to a lack of lubrication, leading to noisy metal-on-metal contact. Therefore using the correct grading of oil for your engine is essential for smooth operation.
Simply changing your oil can also get rid of the tapping sound, as over time an engine that is neglected of maintenance will begin to clog up its oil filters meaning that a build-up of grime can again lead to a lack of component lubrication. An oil additive can also be used to clean valves, rockers and tappets without affecting the viscosity of the oil, keeping the valvetrain in silent harmony.
If these changes make no difference to the tappet noises, a full tappet adjustment should be the next move. Using a feeler gauge to wedge between a rocker arm and the valve stem, a factory setting can be found through a workshop manual to adjust the valve adjustment screw to the correct clearance. And if your engine STILL rattles after the adjustment, you’re looking at large labour costs for tappet, valve or even camshaft replacements.
Engine tappets can be one of the most annoying aspects of older car ownership and although they may seem simply an inconvenience to start with, they should be addressed as soon as possible if you care about your powertrain.
Considering how simple most of the fixes are for these unwanted rattles, standard maintenance checks should see you and your car experiencing many years of smooth motoring. But if your engine ever starts getting its rattle on, you now know what to look for!