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 | BMW Camshaft |
Difficulty Level: 5 |
| This article is the one in a series that will be released in conjunction with Wayne's upcoming book, 101 Projects for Your BMW 3-Series. The book will be 256 pages of full color projects detailing everything from performance mods to timing the camshafts. With more than 350+ full-color glossy photos accompanying extensive step-by-step procedures, this book should be a staple in any 3-Series owner's collection. See The Official Book Website for more details. The book is due out in October 2005. | |||||
[click to enlarge] | I recently had to tear down the top of my BMW 325is M50 engine in order to replace the head gasket (see accompanying tech article - coming soon). Performing this large amount of work, I decided that it would be in my best interest to have a complete valve job performed on the cylinder head at the same time. This requires that you remove the camshafts from the cylinder head. Piece of cake, I thought, until I learned that the BMW camshafts are not like many others that I had worked on previously. Particularly on the six-cylinder cars, the camshafts are very long and hollow. This makes them very susceptible to bending and adverse side loads that can be placed on them during the removal process. After consulting the BMW factory documentation, I quickly realized that BMW requires you to use a special tool in order to remove the camshafts. "No problem," I thought. "I'll just purchase the tool and then rent it out through Pelican for others to use." Well, that well-thought out plan went right down the drain when I realized that the tool costs over $1400 and isn't even available for purchasing at this time. The story I received from our BMW dealer was that the tool is specially made by one guy, in some small company, in the motherland of Germany. There would be an eight-month lead time for delivery of the tool, and even that wasn't guaranteed. In addition to that, you had to buy two tools - one for the four cylinder engines, and an adapter add-on tool for the six cylinder engines. Being the cavalier defender of the Do-It-Yourself mechanic, I decided that there had to be a better way to do this without using the tool. I dove into research, and inquired to many shops and BMW owners about how they have removed the camshafts. Just about everyone I spoke with told me that they either took their car to the dealer, or in one case, had the tool themselves. Hmm, not promising information. I even heard of one story where a poor soul took his 325is to a shop to have the camshafts swapped out - and they broke them removing them. To add insult to injury, they told the fellow that they weren't responsible, and that he had to buy new ones. I'll bet these dolts didn't even bother to check the BMW factory documentation (or even the Bentley manual) to find out the proper removal procedure. Okay, so at this time, my goal was to find a way to safely remove the camshafts without using the tool, and without breaking or damaging them. I'll spoil the suspense right now - I achieved successful removal and installation using a special technique I developed after studying the camshafts for quite a few nights (and a few failed ideas, which I will explain in a few paragraphs). Especially encouraging was one story from a fellow who had seen a BMW racing crew carefully and quickly swap out camshafts in the pit without using the special tool. With this knowledge in hand, I had a feeling that I would be able to figure out a way to achieve this goal. If it sounds like I'm boasting right now - it's because I am - just about everyone I spoke with said not to try it. I just figured, "what's the worst that will happen - I'll just break some camshafts." I wanted my readers and customers to know what would work and what wouldn't work, without all the myths and hype. Let me pause for a second though to give the standard disclaimer. BMW doesn't recommend that you use this method for removing your camshafts. If you don't do it correctly, you can break your camshafts. While this won't destroy your engine, you'll have to replace them ($500 or so apiece, new) before you can run your car again. This would probably be the worst-case scenario. However, if you are careful and smart, and follow my directions and precautions precisely, you should be able to achieve the same successes that I did. Note: I am not responsible if you use this method and you end up breaking your camshafts. | |||||
| Anyways, let's talk for a moment about why the camshafts break, so that we can discuss the methods used to prevent this from happening. As mentioned previously, the camshafts are hollow, and very long (Figure 1). Camshafts are also hardened, which makes them very brittle and prone to cracking. Although I have never broken a camshaft, I would guess that they would break much easier than they would bend, due to the hollow geometry combined with the metal hardening processes. If you place a force on one end of the camshaft, and another force on the other end of the camshaft without adequate support in the middle, you will slightly bend and break the camshafts. The key to safely removing the camshaft is to reduce the uneven forces that are placed on it during the removal process. Where do these forces come from? They come from the preloading of the valve springs. The camshaft can rotate, obviously, through 360˚ of motion. During 100% of this time, there is at least one pair of camshaft lobes pressing down on valve lifters and compressing a pair of valve springs. Transmitted through the lifters, the springs place a tremendous amount of force on the camshaft. The camshaft is supported evenly by the bearing cap that lies between each camshaft lobe. If the camshaft is cocked, or if the force is not evenly distributed across the length of the camshaft, then the camshaft will bend and break. | |||||
| To understand what we need to do, I would first like to discuss how the factory tool works. Figure 2 (11-3-260) and Figure 3 (11-3-270) both show drawings of the BMW factory tool. The tool shown in these drawings is appropriate for the removal of camshafts on four-cylinder cars. The tool bolts onto the head near where the spark plugs are mounted. A handle on the tool then activates a set of rods that press down on all of the individual bearing caps that hold the camshaft to the head. At this point, with the tool in place, you can remove all of the nuts that hold each of the cam bearing caps in place. With the tool applying uniform pressure and force to each of the cam bearing caps (very important), you can release the rods slowly and let the camshaft rise off of the lower cam bearing surfaces. The tool applies even, uniform pressure across the entire camshaft during the removal process. When the camshaft lobes are no longer compressing the valve springs, then you can safely remove the camshaft, as it will have no more forces placed on it. Make sense? It does to me. However, understanding the problem is only the first step. One would think that you could achieve the same results as the BMW tool by simply unscrewing all of the bearing caps uniformly. For example, each nut would be turned 1/2 turn until they were all removed. I must admit, in theory, this seems like it would work very well. However, from the research that I did, I found out that this is almost a sure-fire way to break your camshafts. It seems that simply uniformly removing the bearing cap nuts does not guarantee uniform pressure on the camshaft. I didn't hear too many of the specifics, but I did hear that there were quite a few camshafts broken using this method, so I quickly rejected it. | |||||
| The problem lies with the tension that is placed on the camshaft by the valve springs. Reduce or remove this tension, and you should be able to safely remove the camshafts without them breaking. How to achieve this? Well, I first thought about fashioning a tool that would fit between the valve and the seat on the cylinder head. Such a fork-shaped tool would effectively hold the valve open and compress the seat. However, the tool would have to be manufactured out of a soft plastic-like material like Delrin, otherwise it may damage the seat in the head. My second idea was to use rope - marine rope to be precise, considering that it's available in many different thicknesses. With the head out of the car, you turn the crankshaft until a particular valve is open. Then, wrapping the valve with rope, you rotate the crankshaft and let the rope compress between the valve and the seat. My attempt at this is shown in Figure 4. For all intensive purposes, this does work. It safely keeps the valve slightly open and the spring slightly compressed. However, this technique didn't appear to keep the valve open enough to make too much of a difference on the force that is exerted on the camshaft. Besides, a number of problems exist with this method. You can only do this when the cylinder head is removed from the engine. You can only do this when the valve is compressed, which would make the insertion of the rope (or Delrin tool) difficult to do without an appropriate spring compressor. | |||||
| After wrestling with the rope for several hours, I decided to give it a rest and see what else I could do. After many hours of pondering, and thinking, I began to wonder exactly how many valves had to be held open in order for the camshaft to not have any load placed on it. During normal operation, valves open and close. When the valves are closed, they do not place any load on the crankshaft. So I got to thinking, "is there a spot on the camshaft where only one set of valves are open at a particular time?" The answer is yes - and that is key to the removal technique here. The theory is that if only one set of valves are open at a time, there are no forces or loads placed on the crankshaft from any other lifters. Since each pair of cam lobes is supported by a single cam bearing cap in the center (Figure 5), slowly removing this bearing cap will leave equal pressure on both sides over a very small distance - basically making it impossible to break the crankshaft. | |||||
| Huh? This is one of those techniques that I have had great difficult explaining to people without the cylinder head sitting in front of me. Let's take a look for a moment at Figure 6. In this photo, the cam lobes for cylinder number one are shown with red arrows. The ones for cylinders 2-6 are shown with green arrows. For the purpose of removing the camshaft, you want to rotate the camshaft by using a wrench to grip the square end, as shown in Figure 7. If the head is out of the car, make sure it is supported on two small blocks of wood (Figure 8), so that the valves don't try to lift the head up in the air off of your table from the opposite side. Rotate the camshaft so that the cam lobes for cylinder number one are acting on the valves for cylinder number one. At this point, it doesn't matter whether you're working on the intake or exhaust side. There should be a point in your rotation where the cam lobes are acting on valves for cylinder one, and all of the other valves (2-6) are closed. At this point, the valves for cylinder number one should be slightly open (not fully open). How can you tell if the valves for cylinders 2-6 are closed? Easy - I just stuck my pinky finger down behind the camshaft lobe and tried to rotate the camshaft lifter in its bore. There will be a small clearance between the lifter and the camshaft when the valve is closed and no camshaft lobes are acting on the lifter. This will allow the lifter to be rotated in its bore by your finger. There should be one spot on the camshaft where you can rotate it, and all cylinders two through five should have the valves closed, and the lifters free to spin with your finger. | |||||
| A word of caution here. The camshaft will be heavily spring-loaded due to the fact that cylinder number one has two valves compressed and open. In addition, the cam lobes acting on cylinder number one will be cocked off at an angle, meaning that the camshaft will be spring loaded, and can snap back into another position if not tightly held in place. For this reason, I recommend that this be a two-person job. One person holds the camshaft in place (Figure 7 and Figure 9), while the other person removes it. If not, then the camshaft can rotate while you're removing it, and this may cause it to become compressed against some valve springs and break. In addition, when you're feeling the lifters with your finger, if the camshaft rotates quickly back into place (snaps back), you may end up crushing your finger. Go with my advice here - two person job. On my 1993 325is, I was able to find this "sweet-spot" where there was no loads placed on the camshaft, except for the valve springs from cylinder number one. While all of the BMW 3-Series camshafts are similar, they may have different profiles, where this sweet-spot doesn't exist. In this case, you need to find the spot closest to the "sweet-spot", where the valves for cylinder number 2-6 are all barely compressed. There will be one of these spots on your camshaft. | |||||
| To remove the camshaft, simply put the camshaft into it's "sweet-spot" location and remove the cam bearing caps for cylinders 2-6. There should be no loads on these caps, and after an initial loosening, the nut should be able to be removed easily by hand. Make sure that your assistant is holding the camshaft secure and steady so it doesn't slip (Figure 10). If it slips at this point, the lobes will try to compress the valve springs with no support on the camshaft and it will surely break. | |||||
| Turning your attention to cylinder number one, slowly begin removing the bearing cap. Alternate between screws and turn each one a quarter turn at a time - this will ensure that both sides of the cam bearing cap receive equal pressure. The camshaft should slowly lift up as the valve springs pull the valves back into their seats in the head. If it doesn't, then give it a very light tap with a very small hammer to loosen the bearing cap (Figure 11). Continue until the bearing cap can be removed. The nuts will go very close to the end of their travel on the stud before they will be able to be removed by hand (Figure 12 and Figure 13). This is normal. When the bearing cap is removed, there should be nothing holding the camshaft to the head, and you can simply remove it from the head (Figure 14). Don't drop it on the floor. Alternate Method: If you can't get to a point where all of the lifters for cylinders 2-6 can rotate in their bores, then you need to slightly alter the previous procedure. Instead of removing all of the bearing caps for cylinders 2-6 all at once, use the following method. Put the camshaft in the rotation as close as possible to the point where there are no cam lobes acting on the lifters. This will be the point where cylinder number one lobes are acting on the camshaft, but the rest of the cylinders are placing very little force on the lifters. This will minimize the amount of force on the camshaft. Remove all the bearing caps for all cylinders (1-6) by turning each nut counter-clockwise a quarter turn, turning each and every nut only one quarter turn before continuing. In other words, turn all of the screws one quarter turn, then repeat in the same order. Installation of a camshaft is performed in the opposite manner of removal. Set the camshaft on the head so that the lobes for cylinders 2-6 are as far away from the lifters as possible. The lobes for cylinder number one should be pointing downwards at an angle. Begin tightening the bearing cap for cylinder number one, a quarter turn on each nut, alternating as you go. Constantly check the lifters as you tighten down the camshaft - they should be free to rotate in their bores if you have aligned everything correctly. If you used the alternate method detailed above, then repeat the alternate method for installation - tighten each of the bearing caps for all of the cylinders one quarter turn, and then repeat. Camshaft bearing caps should be tightened to 11 ft-lb (15 Nm), as shown in Figure 15. This procedure should work very well, particularly if the cylinder head is out of the car (Figure 16). You can perform this procedure if the engine is in the car, but it makes it quite a bit more difficult to navigate (Figure 17). One note of caution - if you do perform a camshaft swap with the engine in the car, then you will want to make sure that you don't accidentally tap your valves to your pistons. In order to be 100% safe, you should turn your engine clockwise to top dead center (TDC) for cylinder number one. Figure 18 shows the main crank gear with the TDC mark (green) pointing towards the notch on the engine case (red arrow). Now rotate the engine about 45 degrees clockwise. This will move the pistons about half-way in their bores so that they won't have any danger of touching the pistons - no matter what you do. Well, there you have it. I hope that this wasn't too confusing. If it was, then send me an email at wayne@pelicanparts.com and I will do my best to clarify some of the concepts here. This technical article is made possible solely through the support of Pelican Parts. If you like what you see here, then please visit our online BMW catalog and help support the collection and creating of new and informative technical articles like this one. | |||||
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