If you drive an older BMW, chances are that you’ll need to adjust your valves periodically to keep the engine running smoothly. To do this, you’ll need to remove the valve cover gasket and go hands-on with your valve train. Needless to say, not many owners perform this procedure themselves.
However, the truth is that a valve adjustment is a relatively straightforward process that you can carry out on your own if you have the right tools. This article covers the importance of a valve adjustment, the signs that indicate you might need one, and a step-by-step process that can help you save on labor costs.
What is Valve Adjustment?
As your engine operates, the intake and exhaust valves, driven by the camshaft, are constantly being opened and closed. Over time, they can wear out, and their opening and closing actions will become less efficient. The process of rectifying this is called a valve adjustment.
Most modern cars feature hydraulic lifters, which eliminates the need for manual valve adjustment. Hydraulic lifters use a self-adjusting mechanism that’s actuated by oil pressure. Older engines, like the BMW M20 or M30, feature followers and rocker arms that are moved by the camshaft, opening and closing the valves. As mentioned above, this system comprises several moving components that can become less efficient over time.
When you carry out a valve adjustment on your BMW, you adjust the clearance between the cam lobe and the rocker arm, ensuring that the valves are properly opened and closed. This clearance has to be checked and adjusted manually with the help of a tool called a feeler gauge. A feeler gauge set features multiple thin blades of different widths and measures narrow gaps or clearances. Using one may seem daunting initially, but you should get the hang of it without too much trouble.
The inlet valves in your engine determine how much air-fuel mixture is sucked into the engine for combustion, and the exhaust valves allow the combustion gasses to escape the engine. Suppose there is an issue with valve clearance. In that case, it can alter how effectively these mixtures enter or exit the engine, resulting in reduced performance, rough idling, and premature wearing of the engine’s internals.
When Should You Adjust Your Valves?
The manufacturer-recommended valve adjustment interval will vary from engine to engine, but BMW typically recommends that you carry one out every 30,000 miles. However, it’s recommended that you use this figure as a reference, as the actual intervals for your engine will vary mainly depending on your driving style, conditions, and overall engine maintenance.
That said, it pays to know how to recognize signs of noisy valves in dire need of adjustment. Here are a few pointers.
Noisy Valves and Other Signs of Out-of-spec Valves
The symptoms that your valve clearance is not in tune are rather noticeable. If the valve clearance is under what’s required, the flow of gasses and vapor through the combustion chamber will be restricted, resulting in rough idling and a drop in performance.
Meanwhile, if the clearance is too much, the valves will be noisy, and you might hear a clattering sound from the engine. Of the two, greater valve clearance than required can have more detrimental effects on the engine, as it can wear out the valves, cam lobes, and the rocker arms sooner.
You should get a valve adjustment done as soon as you notice any of these problems to prevent the likelihood of any other mechanical issues.
How to Adjust the Valves
Performing a valve adjustment process on your BMW is one of the more technical aspects of maintaining your car as you work on the engine’s internals. However, with the right tools, a little time, and a lot of patience, it’s a process that will only help you appreciate your Bimmer even more. If you don’t know where to start, here’s a step-by-step process on how to carry out a valve adjustment on your BMW:
- The first and most crucial step in performing a valve adjustment is to ensure that you’re doing it on a stone-cold engine. As you know, heat causes metal to expand, and if your engine was running recently, and it’s warm, the clearances you set may be exaggerated. So, before you adjust valve clearance, park the car where you will be working on it a day in advance.
- When the engine is cold, remove the valve cover to access the entire valve train. Once the cover is removed, visually inspect the valve train to ensure that none of its parts show unusual wear or signs of excess damage.
- When adjusting the valves, they must be at TDC or Top Dead Center. This is when the broader end of the cam lobe is resting on the rocker arm and the pointy end is directed straight down. To achieve this, you will have to rotate the crankshaft. You can do so by putting the car in neutral and turning the crankshaft bolt manually.
- Use the feeler gauge to check the current valve clearance specifications. This value will vary from one BMW engine to another, and a quick online search should give you the required values for your car. For instance, the M10 engines work well with a valve clearance of 0.006 to 0.008 inches, while the M20 engines require a slightly looser 0.010 to 0.012 inches clearance. You should check the clearance of all the valves in your engine, from one cylinder to the next, following the engine’s firing order. The six-cylinder M20 engine, for example, has a firing order of 1-5-3-6-2-4, so that’s the order of cylinders you will check.
- To check the clearance, slip the correct feeler gauge strip into the gap between the rocker arm and the valve stem to determine the gap. If you find that any of them have a clearance that is too high or too low, it will have to be adjusted.
- Adjusting the valve clearance will require a 10 mm wrench and an Allen key. On the valve that needs adjustment, loosen the eccentric bolt using the wrench. Then use the Allen key to move the adjusting hole to tighten or loosen the clearance — moving it towards the engine head will reduce it, and the opposite will increase clearance.
- As you adjust the clearance, continue to use the feeler gauge to determine if the desired clearance has been set. If it has, use the wrench to tighten the eccentric bolt on the side to secure the set clearance.
- Repeat the process for the rest of the cylinder in firing order. Before you close the valve cover, clean the edge of the valve train housing so that the new gasket and cover will sit properly and not result in an oil leak.
How to Tell If your Bimmer Needs Manual Adjustment?
Most modern-day BMWs come with hydraulic valve lifters that don’t require frequent valve adjustments. That’s not to say these engines will never need one — if supporting components like the rocker arm or camshaft are being worked on, the valves will have to be adjusted. That said, the process of adjusting hydraulic valves is slightly different.
If you bought your Bimmer before the turn of the millennium, it probably needs manual valve adjustment. Either way, it’s a good idea to keep an eye out for the signs of improper valve clearance mentioned above to avoid more severe mechanical issues with the engine.
