Over time, the valves on your F2/F3 are going to go out of adjustment. The interval to check is usually about 11,000 miles. While this can be performed at home, there are some challenges to be aware of before you begin.

Engine Overview:
Let's begin with a brief overview of the vavletrains design. The F2/F3 is a dual overhead cam, 16 vavle 4 cylinder engine. That means each cylinder has 4 valves (two intake vavles located under the intake cam and two exhaust valves located under the exhaust cam). The lobes of the cam rotate directly against the end of the valves caps, which shroud the valve spring. Between the valve cap and the valve spring are the valve shims. These are available in various thickness as the means to get the correct valve lash (desired adjustment) between the valve and the lobe of the cam. The shim design is very small, light, simple, reliable and effective. This wastes little power to actuate the valve.

Valvetrain Design Considerations:
The reason lash is important is due to an engines heat cycle. As metal heats up, it expands. If there were no gap then the expanding metal would start holding the valves open all the time and you would loose compression/power. Have too much of a gap and the valvetrain will be noisy, not open all the way and loose power. You might ask yourself, how come they do not automaticlly adjust... this to is possible. Passenger cars often run hydraulic lifters which use a little bit of power to adjust the vavle while the engine is operating, at the expense of making the valvetrain heavier.

Gotchas for the Home Mechanic:
The first gotcha is in the design. Many shops and dealers will not have the shims you need in stock. This would require dissasembling the bike and valvetrain to take measurements, ordering the shims, reassemble the bike, wait for the shims, disassembe again and finally install the new shims. Or you can leave the bike apart while you wait.  Don't get discouraged if that poses a problem, you can sometimes get lucky and simply rearrange your existing shims to do the whole job. It at least will reduce the cost of new shims if you can reuse some. See the case study at the end of this article for a real world use case of how it is done.

Tools Needed:
     Ratcheting Socket set
     10mm socket.
     14mm socket
     Metric Feeler Guage
     Micrometer (digital is best)
     Good strong small magnet

Let's Begin:
     This can all be done with the bike on the kickstand. You will first need to get to the valve cover. On the F2/F3, this means removing the tank, the airbox from the carbs and the coils. Make sure to mark the plugwires, coils and wires to each plug on the coils before removing them. This is so that assembling them later is very easy and fast. You will need to unbolt the radiator from the frame but you do not need to drain it. Simply allow it to hang down out of the way. If you have an F3, then also remove the ram-air below the neck. You should now be able to remove the 6 10mm bolts on the valve cover and lift the cover off. On the right side of the engine, remove the circular timing cover by its 17mm formed in head. This will give you visual access to the timing marks.




Measuring:
     Before you can measure, you must get the engine at top dead center for the #1 and #3 cylinders. Each cam gear is marked as "IN" for intake and "EX" for exhaust. Turn the engine over using the 14mm bolt exposed under the timing cover, rotating clockwise (tightening). Align the "Tl" on the pulse rotor with a line "l" on the outer cover at the 2 o'clock position. When the "IN" on the left side of the left cam gear is lined up with the surface of the top of the head, and the "EX" is also lined up but on the right cam gear on the far right side of the head and the "Tl" is lined up at the pulser cover then you are ready to begin.

 


Get a piece of paper and draw two rows of 8 circles on it to represent each vavle on the bike. Since you will be working mostly from the front of the bike, mark the top row intake and the bottom row exhaust. Now number the circles left to right on each row, starting with 4a, 4b, 3a, 3b, 2a, 2b, 1a, 1b to represent each vavlue uniquely.

Now measure the #1 and #3 cylinders intake valves with your gap tool by inserting a .16mm shim under between each cam lobe and vavle spring cap. Remember, the numbers of the intake vavles when looking at the valves from the front of the bike is the same as on the paper. If the .16 wont fit, then try a smaller one. If its too loose then try a bigger one. Document your gaps above each of the related circles on your paper.





Now turn the timing mark 180 degrees clockwise so that it is opposite the case mark. Now measure the exhaust #1 and #3 amd document those results.




Now turn the timing mark clockwise 180 degrees to the timing mark. Note the cams are not lines up as In and EX. We are 360 degrees off of #1 top dead center which allows us to now measure the #2 and #4 intake. Write down your results.



Now turn the timing mark 180 degrees to be once again opposite the case mark. Measure #2 and #4 exhaust valves and write this down. Turn the timing mark clockwise 180 degrees to where the timing mark matches the case mark, and the IN and EX marks on the cam gears line up with the top of the head. You are back to the begginning.



Once this is complete, it is time to pull the cams retianers out one at a time. Start by loosening the cam chain tensioner on the right rear of the engine. To do this, removethe single bolt at the tip of the unti. This exposes a hole down to a small flathead which is sprung to stay exteanded. By twisting the flathead you can unload the spring which allows the tensioner to release internally. Loosen this all the way and brace the screwdriver to the frame. This should hold it sprung open while you work as well as relieve tension on the cam chain.




While I removed both cams, you can do just one cam at a time and let the other cam hold the chain up. It goes much quicker this way. For the sake of the write up though, I removed both for clarity. Remember, the cam gears say IN and EX so you cant mix them up. Now remove the exhaust cam retaining bolts careful not to drop them in the engine. Once removed, lift the cam up opposite the cam gear to allow a little slack in the chain. Unhook the chain from the cam gear and remove the cam.  Take a moment to look the cam lobes and bearing surfaces for signs of wear. They should be smooth and free of any discoloration or grooves. Aslo check the teeth on the cam gear for wear.

 

Remove the intake cam in the same manner and set it aside.  If you remove both cams, then zip tie the cam chain to a cable or anything above the head to keep it from falling in.



Using the magnet, remove each spring cap and place it somewhere that you can keep the orientation of which valve it came off of. I lined mine up below the engine on the floor for now- but later moved them to a marked box the kept them oriented correctly.



You do not want to mix these up so make sure you can remember which one came off of which valve - or else you will have to start over. Now carefully remove the shim from the underside of each retainer (it make have remained on the valve).
      


These have numbers on them but wear and tear usually rubs them off. If you can see the number, great. If not, then measure its thickness with the micrometer and document it on your gap sheet in the middle of each respective circle.


   

Now that you have all these measurements, its time to make sense of them. What we need to do is figure out which shims need to be changed and which ones can be reused. this way, we know what to order.

Below is a Case Study of my 97 CBR 600 F3 as a direct example of how the above is applied. Here are my initial measurements:

Target Gap: 0.16mm   +/- 0.03mm (0.006 in +/- 0.001 in)
Intake#:   4a     4b     3a     2b      2a      2b      1a       1b
Gap:       .12    .10    .12    .15     .15     .15     .12     .15
Shim:     2.10  2.21  2.15  2.13   2.08   2.08   2.13    2.08

The measurements above show 4b to be too tight and a few others to be on the tighter side.  In order to make it as close to perfect as possible. I would have to reshim it as shown below. Keep in mind that plus or minus 0.03mm is acceptable so a value of .13 to .19 is considered good. That being the case, this is how I configured mine:

Intake#:   4a     4b     3a     2b      2a      2b      1a       1b
ReGap:   .16    .16     .17    .15     .15     .15     .16     .15   
Reshim: 2.13  2.15   2.10   2.13   2.08   2.08    2.09    2.08                           

I used 1a's 2.13 and put it in 4a, 4a's 2.10 from 3a, 3a's 2.15 from 4b. That mixing corrected all but one, and leaves me buying a single 2.09 shim to use in 1a. That completes the intake. A 2.21 shim remains and is unused. See how that worked?

Next is the Exhaust:

Target Gap: 0.22mm   +/- 0.03mm (0.009 in +/- 0.001 in)
Exhaust#:  4a     4b     3a     3b      2a      2b      1a       1b
Gap:         .17    .22    .25    .25     .22     .22     .25      .27
Shim:       1.7    1.85    2       2       2        2      1.85    1.85

As you can see above, 4a is way too tight, and 1b is too loose. A few others are slightly off as well. This is not uncommon as F3 exhaust valves are known to wear faster. As the valve wears, it sinks into the head. It's stem gets closer to the cam and the lash decreases.

So lets do the same thing as the intake.

Exhaust#:  4a     4b     3a     3b      2a      2b      1a       1b
ReGap:     .22    .22    .23    .23     .22     .22     .22      .22                     
Reshim:   1.65   1.85  2.02  2.02     2        2      1.88    1.90                                   

It looks like I'm going to need to order a few here as well, since nothing crosses over.
Since I needed about 6 shims, and they are $8-$12 each depending on where you go (I went to a Yamaha Dealer as they use the same size and seem better stocked), it made sense to spend the $80 on a complete shim kit. This comes with 60 or so shims of all sizes in .05mm increments. This turned out to be the smarter thing as measuring the new shims showed they did not actualy measure as marked. By measuring the true width, I was able to get all my valves within +/- .01mm. Much better than originaly expected.

After swapping in the shims, replace the cam being carefull to realign the marks at Top Dead Center (TDC). Now run through the motions of checking all your intake gaps again. If you made a miscalculation, you will find it now. If you did it right, all your measurements should be within tolerance. If not, recalculate based upon the new measurements, remove the cam and just work on those that were off.


After everything was completed and the bike reassembled, it ran smooth as silk. A job well done and a good $500 remains in my pocket for doing it myself!

Take your time, and measure everything twice.