Today’s modern 4-stroke motors produce heaps of usable power. Most riders can get by using the engine as it comes from the factory in stock form. But what if you are a woods rider looking for more low end power or perhaps you ride MX or you are a desert rider and want more top end and over-rev. How can you fine tune your motor to suit the type of riding you most often do without breaking the bank? The simplest way is to install a set of cams.
Changing your cams gives you the ability to fine tune the power delivery characteristics of your motor. This is achieved through varying valve lift, timing and duration the valves open. We recently visited Chad Watts of Watts Perfections for some help installing a set of Hot Cams in our 2008 YZ250F. We brought along with us EDM Shop Girl, Lauren to demonstrate the process of installation. If she makes it look easy, it’s because it is. Just be sure to have a clean work space, a service manual (we use Clymer Service Manuals), more time than you think you will need and lot’s of patience. You don’t want to rush through this! If you make a mistake the result could be catastrophic, causing severe engine damage.
Cam installation can be done to your motor while it is installed in the chassis, we removed ours for the purposes of this article. It makes the service a bit easier and gives us room for the photography.
The first thing you want to do before starting any work on your bike is give it a good cleaning. The last thing you you want is a nice chunk of dirt falling into the motor because you were working on a dirty bike. Check here for our Bike Wash Tech Tip with EDM Shop Girl Laurie.
The next thing you want to do is read through the process in your service manual to get a general understanding of all that is involved.
Remove the seat, gas tank, and shrouds and give your bike a good wash, allow to dry or blow off any water with compressed air. You will need to drain your radiators and disconnect the hoses. Keep the radiator fluid in a clean container to re-use. Removing the radiators is not required but it is a good idea in order to get them out of harms way. You will also need to remove the sub-frame, air box and carburetor.
Here we are going to locate top dead center (TDC) so we know the piston is in the correct position for re-assembly. Attach a tool to the crank shaft and rotate counter clockwise, while gently inserting a screwdriver into the cylinder to feel the piston as it rises to TDC.
Be very careful when removing the retainer! Yamaha’s have a steel crescent that sits inside the cam retainer to keep the cam in place. This small crescent is held in place by a small amount of tension, often not enough to keep it there when you lift the cam retainer from the motor. It can easily fall into the motor adding hours to this service. Go slow, watch for it and be careful!
Take your new cam and coat it with fresh motor oil, then place it into the cam cradle aligning the dots on the cam with the top edge of the cylinder. Do this for both cams. You may have to try a few times to get both positioned correctly. Double check the crank location to confirm it is still at TDC. One tooth off will affect timing and could cause a catastrophic failure. Dont’ be in a hurry and double check your work!
At this point we can double check your work to be sure nothing really bad can happen when you start your bike the first time. Place a wrench on the crank bolt and turn it counter clockwise to rotate the motor. We are looking to see if it operates smoothly without locking. If you have done something terribly wrong you want to find it while you are gently turning it over by hand. It’s unlikely you will damage a valve by turning it over this way. Kicking it over with your foot is another story…
Rotate the motor a few times. If everything seems fine, place a tool into the cylinder and feel for the piston to find TDC. Check to make sure the timing mark on the crank is lining up at TDC. Then look to see that the cam lobes are facing outward away from the piston. If you have all of this, the timing and your assembly is correct.
Finally we are finished. Install your valve cover and re-attach your radiator hoses, shrouds, gas tank, seat etc. Kick your bike over and listen to it purr…
A special thanks to Chad Watts for his technical support, to Hot Cams for the product, to Industrial hard carbon for the DLC on the cams, and to Monarch Talent for letting us borrow Lauren for a few hours.