Adjust the Valves on BMW /5 Airhead Engines
If you own any one of BMW’s /5 twins from the Seventies you’re in good company, because when it comes to basic maintenance, few motorcycles are easier to work on. Simple and robust, they’ve become the poster child for sound German engineering.
Yet, like any machine, they require routine maintenance, and for this How-To we’ll take you through the process of adjusting the valves on a 1973 BMW R75/5. While BMW’s original maintenance schedule called for checking/adjusting the valves every 8,500 miles, we tend to operate on a 5,000-mile schedule if only because adjusting the valves on these bikes is so easy. The basic steps we follow here apply to just about every BMW airhead made from 1969 to the end of airhead production in 1996. While BMW constantly improved and changed the airhead engine over its long life, the basic architecture — and methods of maintenance — remained the same.
We should note that while the valve train on these BMWs is very reliable, one issue that plagued early engines was excessive noise from the rocker arms, caused by excessive end-float of the rocker arms on the rocker arm shaft and supports. If your valves are properly adjusted but you’re experiencing excessive noise from the rocker arms, there are several methods to alleviate the issue. We won’t cover those here, but there’s a good discussion of the issue at this BMW motorcycle repair information site. This problem was mostly limited to models built up to about 1974, when BMW changed the rocker arm support.
This is one job that won’t break the bank, with replacement parts limited to a set of valve cover gaskets: Factory gaskets list for $5.07 each.
It’s also important to note the discussion surrounding valve clearance settings. BMW originally specified a clearance of 0.006-inch for the intake valve and 0.008-inch for the exhaust valve for all the /5 engines. Our Clymer manual suggests a tighter 0.004-inch for the intake, but BMW dealer John Landstrom of Blue Moon Cycle in Norcross, Georgia, says to use 0.005-inch on the intake and 0.007-inch on the exhaust. The difference is probably debatable, but we followed Landstrom’s advice, appreciating it comes from years of experience with these bikes. Note that all work is done with the engine cold and at normal room temperature.
Assuming everything is otherwise normal, this is a very straightforward operation and one that’s easily within reach of the novice mechanic. You will need at least one specialty tool — a torque wrench — and you’ll need a basic selection of metric socket wrenches, feeler gauges, an oil pan, some oil in case you have to top off the engine and, if you’ve never replaced them, a new set of valve cover gaskets. The valve cover gaskets on these engines can be reused many times over, so if you know your engine’s maintenance history you can forego replacing them. Either way, at a little over $10 a pair they won’t break the bank. As to time, we’d suggest budgeting a couple of hours for this job. You can do it faster, but there’s no value in rushing it, especially your first time through.
As always, we suggest having a good shop manual on hand to aid in parts identification and proper torque specs.
1. To adjust the valves you’ll need to turn the engine over several times. Remove both of the spark plugs so you don’t have to work against compression.
2. Next, place an oil pan under the cylinders and remove the three nuts holding each valve cover in place; two 10mm nuts at approximately 10 and 4 o’clock at the rear of the cylinder fin and a larger 14mm nut in the center of the valve cover.
3. With the nuts removed the valve covers should separate from the cylinder head easily. If the cover is stuck to the head, give the cover a gentle whack with a rubber mallet or a block of wood. Let any oil that’s pooled in the cylinder head drain out.
4. Before adjusting the valves you need to retorque the cylinder heads. Start by loosening the six 14mm cylinder head studs. Following a cross pattern, break each of them free 1/4 turn.
5. Next, retorque the six head bolts. The BMW owners’ manual says to torque to 25ft/lb-28ft/lb. Our Clymer manual gives a range of 26ft/lb-29ft/lb. We split the difference and torqued them all to 27ft/lb, working in a cross pattern.
6. Now it’s finally time to adjust the valves. Remove the black rubber plug in the engine block just behind the oil dipstick. Rotate the engine until the letters “OT” are centered in the access hole. This is top-dead-center for one of the cylinders.
7. The valve rockers on the cylinder that’s at top-dead-center will both be loose. You can feel this easily by rocking them on their shaft. Once confirmed, use feeler gauges to check the valve clearance on the intake (0.005in) and the exhaust (0.007in) of that cylinder. If either needs adjustment, release the 12mm locknut on the rocker arm adjuster.
8. With the locknut released, use a 12mm wrench (or your fingers) and turn the adjuster until the appropriate feeler gauge is just pinched by it. It should slide with a light drag. Lock the locknut, then rotate the engine through a full turn until the letters “OT” on the flywheel line up again and repeat the process for the other cylinder.
9. With the valves for both cylinders adjusted, it’s time to button things back up. Wipe the valve cover mating surfaces clean and place a new gasket (if necessary) on each valve cover. Reinstall the valve covers and the three nuts securing them. Tighten the nuts evenly, being careful not to overtighten them. They need to be snug only, not wrenched tight. Reinstall the spark plugs and that’s it, you’re ready to roll!
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