With quality tools, a clean...
With quality tools, a clean work space and proper attention to detail, valve adjustment is not that difficult.
When modern four-stroke off-road bikes arrived, most featured some sort of shim-type valve adjustment. Screw-type adjusters at the end of rocker arms that we learned on are a thing of the past. Those adjust with a threaded tappet and a locknut. That is a dead-simple way to do the job, but not one well-suited to ultra-high rpm. Most performance four-strokes use a precision steel shim to manage the clearance between the valve stem and a metal bucket or tappet that slips over the valve spring. The shims can't come out, and they offer positive adjustment. The downside is that you need to have shims on hand, or make a trip to the dealer to get some. A single shim is less than $10, and shimmed valves generally don't need adjustment very often. We find it ultimately more economical and time-saving to keep a Hot Cams shim kit on hand. For the price of a few shims, you get all you will ever need. As we have lived with and worked on more varieties of four-strokes, we have learned of some tips and tools that make this job much easier. To check or adjust your bike, wash it thoroughly, clean and organize your work space and dig up your manual.
 01 Remove all the parts in...  01 Remove all the parts in the way of the valve cover: seat, tank, shrouds and, on some models, the radiators. Undo the bolts and pop off the valve cover taking care not to damage the rubber gasket. Unscrew the timing plugs in the ignition cover, and use a T-handle or socket to rotate the crankshaft until the marks for Top Dead Center (TDC) are lined up. |  02 Use a feeler gauge to...  02 Use a feeler gauge to measure the gap between the cam lobe and the tappet bucket. The feeler gauge should be a snug fit where you feel a bit of a pull as it comes out. Feeler gauges that are angled at the tip are a bit easier to use, and the type with a rigid center section like those from Motion Pro work the best. Write down the clearances as you work. |  03 If the clearances are...  03 If the clearances are off from the manufacturer's specs, loosen the bolts holding down the cam caps a bit at a time working in an X pattern. Note that two of the bolts are silver color on this bike. Remember that or make a note, so you can put them back in the same spots. |
 04 As you carefully work...  04 As you carefully work the cam caps up, it helps to thread a bolt back into the valve cover hole to act as a handle to work the cap up. There are usually parts under the caps that can come loose, so be gentle, and when the caps come up lift them slowly while watching for stray parts. You don't want to lose them, and you need to see where they go. |  05 Two of the parts you want...  05 Two of the parts you want to look for are metal half clips which locate the cam bearing and hollow collars, called dowels, which serve several functions. The dowels locate the mating surfaces of the parts, and often they are conduits for pressurized oil or even coolant, so they must be in place for installation. |  06 Before the cams can be...  06 Before the cams can be removed to get at the tappets and shims, the tension must be taken off the cam chain. Remove the cam-chain tensioner's center bolt to relieve the spring pressure; to get the maximum slack, remove the tensioner casting as well. |
07 With slack in the chain you can lift the end of the exhaust cam, angle it and lift it out. You should not need to force anything here. Once the exhaust cam is out, start on the intake cam. The exhaust cam has the automatic decompression system, so it can't be confused for reassembly. Set the cams where they will be safe and stay clean until reassembly.
08 A telescoping magnet works great to lift out the tappets or buckets and shims. Sears has one that is shielded with an outer collar so the very end is the only part that is magnetic. Keep track of the location of the tappets; they need to go back into the same holes if they are to be reused.
09 The shims sit in these pockets, but frequently they will lift off with the tappets when you use a magnet. Make sure the aluminum bearing surface (arrow) shows no wear. Engines that have only one bearing on the cam use high-pressure oil film between this aluminum surface and the steel cam. The surface has to be perfectly smooth to work properly.