A LESSON IN CAMS
Yesterday I learned more about cams than I had in my whole life to that point. I visited Laurie and Steve at Web Cam in Riverside, California so they could show me what they do and how they do it. The non-stop bombardment of information that followed was like being submerged in a big bowl of cam stew for three hours. I’m not ready to grind cams myself, but hopefully some of the knowledge that they fired at me will work its way through my skull for future use. Some of the things I learned:
Billet vs. regrind vs. hard-weld–Most O.E. cams are cast, which is expensive but creates a very hard surface after the process is complete. There’s a large aftermarket that “regrinds” stock cams, which is a process that removes material to reproduce a fresh lobe. The problem is that the inner circle of each lobe ends up being smaller, which changes a long list of specs in the valve train. Hard-welding a cam is a much more difficult process that rebuilds the lobe without affecting the lowest points, and if it’s done right, the lobe actually ends up being harder than stock. A billet cam is machined from scratch. The advantage here is that you don’t have to supply a core. The people at Web Cam offer billet cams, but they are especially proud of their hard-weld process.
Pitfalls of cam replacement–Engine builders often ask Laurie and Steve for custom cams. That’s their main business. They’ll build anything, but you can only do so much with a stock head. A common problem with high-lift cams is “run off.” This is when the new lobe is too tall for the bucket and the leading ramp of the lobe hits before the part that is supposed to lift the valve. This can wear the bucket in record time. A smart engine builder will install oversize buckets when this problem presents itself, but most O.E. buckets are barely large enough to handle stock lift.
Spring issues–When you’re building a high-performance motor the three most important issues to look out for are the valve springs, the valve springs and the valve springs. You need to check the installed spring height because if it’s not within spec, the list of bad things that can happen is long and ugly. A spring that has too much load can mess up the buckets, the cam, the valves and the valve seats. If the new cam has more lift, you can also have coil-binding issues. With the valve fully open, check the clearance between each coil; it should be no less than 0.045″ spread over three coils. And have you ever thought about the clearance between the valve guide and the valve retainer? When the valve is open, the retainer is right up against most stock seats. If there’s more lift, you can simply run out of space.
Clearance issues–Sometimes a great big cam lobe can hit things it’s not supposed to touch. A good example is the Yamaha Raptor 700. A larger cam can actually impact the rocker arm where it mounts and take a big chunk out of it. You should rotate the motor through a few revolutions and inspect everything. The rockers can even hit the valve cover. In the case of the Raptor, the rocker has to be relieved if you install a cam that has any oomph.
Degreeing a cam–A stock motor has cam timing that starts off right on the money. But when you install a thinner head gasket, or when you deck the cylinder, or when the chain stretches, the timing can be off. There’s horsepower to be gained. The art of degreeing in your cam isn’t lost, but few tuners know how to do it. The process is difficult on most dohc motors because the cam gears are pressed in place. They have to be pressed off to be changed. For some motors, slotted cam gears are available.
Web Cam has a great website with lots more information on cams, including detailed instructions on how to degree-in a motor. Check it out: www.webcamshafts.com. –Ron