From the Boutique:

A Note about Cams . . .
by Philip J. Holt

Installing cams in a Sportster is relatively easy. There are some pitfalls and details to pay attention to, though. Sportster engines evolved from an engineering philosophy in the 50's that held that a low part count was an objective and that having components perform more than one function was okay. No matter what year the Sportster, the engine really is a marvel. One of its clever design ideas was to use an individual cam for each valve. This allowed the pushrods to be nicely perpendicular to the cams (improved reliability) unlike big twins, which require pushrods to enter the engine case at wild angles (more stressful).

To stand the engine stresses, the camshafts need to be supported at both ends. The engine case provides that at one end, and the cam cover ended up having to provide it at the other end. An inconvenient consquence is that cams and cam covers are matched exactly for fit at the factory. You can't just replace the cam cover on a Sportster without taking into account how the cams will fit. You know where part of this is headed.

When you buy a new set of cams, they will probably not fit as precisely as the old ones. Measuring cam end-play and using shims when necessary are really important steps on a Sportster. Expect a little more cam noise out of the engine because it is hard to get a perfect fit when you're not computer selecting parts the Harley does at the factory. This doesn't mean that sloppy is okay, just that perfect is harder for those of us who perform these upgrades in the garage with our Craftsman (or occasional Snap-On) tools and whatever cams we got down at the dealer.

Because of how the ignition is set up, you should try to leave it all pretty much together if you can while you change the cams. You can generally just pull the module out of the way but leave everything connected. To do this, you'll need something to rest the cam cover on close to the engine because it can't get very far way when the ignition is still connected. The cover's only going to be off for a few minutes, so this keeps the process simpler. Getting a new cam seal in can be a little tricky when you follow this patch, but a few little improvisations for supporting the cam cover and keeping the ignition module out of the way will make it simple. You must replace the cam seal when you replace the cams. You can try to skip that step, but happy endings with seals and o-rings usually involve new ones.

Some cams (like some Screamin Eagle varieties) don't require you to do anything with the heads. Others will require you to put in stronger valve springs. If you have to do that, you have to take the heads off, so you may as well get them freshened, too. Some cams have enough lift to require you to machine a little out of the top of the rocker box covers to allow room for rocker travel. This isn't uncommon and is only a little bit of a pain.

If you are talking about installing cams, it should be safe to assume that you already have a 1200cc engine with a good carb, exhaust, and ignition setup. The stock carb, properly jetted is great, and doesn't usually need to be messed with. I've had both CV and S&S, and both worked fine. I've used K&N air filters for years--they work fine. Drag pipes are pretty much useless anywhere but running wide-open-throttle on a drag strip. A Screamin Eagle setup is a nice match for the engine. (I have that on my Dyna right now.) I've had great luck with SuperTrapp on a Sportster. Use all the disks and put an open end-cap on it. It made a nice performance difference as well as a great sound. Screamin Eagle makes a good ignition for the Sportster as do various third parties. These will generally bump the rev limit up a little.

Sportsters demand a little more of the rider, but they pay it back with a lot of fun. You probably won't achieve a big horsepower boost by messing with cams, and if you do, it will probably be in a pretty narrow RPM band. The stock cams are perfect for all around riding. Screamin Eagle cams are still mild enough to keep the powerband satisfyingly wide. After that, you get into specialty needs that might mean you'll be able to scorch the tread off your rear tire, but will never quite be happy unless the throttle is wide open all the time.

As always, be familiar with the mechanics at your dealership. Practically all of them wrench on bikes because they love it, and they like talking about it. They do it enough to be great sources of support and advice.

Copyright © 2001 by Philip J. Holt