BMW Motorcycle Owner's of America
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Keep 'em Flying:
Camshafts and the Electric Airhead
By Matthew Parkhouse
(January Owners News)
January 8, 2007

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The camshaft and sprocket, replaced in the engine. The two steering belts are loose in front. The flywheel, oil pump, cylinders, pistons and lifters all have to be out of the way in order to remove and replace the shaft. (enlarge image)
 
Last month I wrote about replacing main bearings in a high mileage Airhead engine. As part of that repair, I also checked the camshaft of this bike. Any time an engine is taken down for this sort of repair, it also makes sense to check the oil pump. The oil pump is driven off the back end of the camshaft, in a compartment machined out of the engine casting. This can be worn or damaged, usually by debris circulating in the oil. The clearance between the pump parts and the casting can wear to excessive clearances, causing a drop in oil pressure. As this was the problem that sent this engine to us, I really needed to check the pump on this BMW. As things turned out, the pump was fine, good clearances despite the 160,000 miles on the engine. However, the machined slot for the woodruff key that secures the inner pump rotor to the camshaft was fractured. This necessitated a replacement of the camshaft. We located a good one from The Parts Haus in Long Beach, California. The camshaft is just that; a long shaft, with machined lobes for activating the lifters and pushrods to open the valves. If one is removing the camshaft from an engine for replacement, the engine has to be pretty well torn down. This can be done with the engine in the frame of the bike. You have to remove the flywheel and oil pump parts; clear away the timing cover and the timing chain; remove both cylinders and pull out the lifters. The camshaft can then be pulled out the front of the engine.

Once the shaft is out and in your hands, it has to be stripped down. The sprocket to run the timing chain is pressed on the shaft. I had to use a press to remove the sprocket from the old, damaged camshaft and install it on the replacement one. This sprocket was almost new as the owner had replaced the timing chain and sprockets fairly recently. A hydraulic press is needed for this task. As the timing sprocket is pressed on, you have to adjust the endplay. The camshaft needs a small amount of free play (0.1mm) to allow easy rotation in its bearing. This is adjusted with a feeler gauge and going back and forth with the sprocket on the press. Once the sprocket is properly mounted, the camshaft is replaced in the engine block. The bearing carrier is held to the engine block with two bolts.

 

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