In this article, I will share the valve adjustment procedure for the Honda CBR900RR Fireblade SC33. Starting with how to check motorcycle valve clearance to determine whether your valve lash is out of spec in the first place, we will then move on to motorcycle valve clearance adjustment.
This guide is specific to the CBR900RR Fireblade, but the basic principles and methods are the same across many bikes, such as my method of creating a motorcycle valve clearance chart to do your workings out when it comes to measuring and changing the valve shims.
For a more concise version, and for those who prefer to watch a video on the topic of CBR900RR valve clearance adjustment, head further down the page and see our video on YouTube!
What Are Valve Clearances?
All internal combustion 4-stroke engines use valves. Most car engines use hydraulic lifters which self-adjust, see our other article about noisy hydraulic lifters to find out more about those. Higher performance cars, and especially motorcycles tend to use solid valve lifters that require valve clearances to be checked and adjusted on a regular maintenance schedule.
This article is about setting the motorcycle valve clearances on Honda Fireblade. The main principles will hold good for all engines that use bucket and shim adjusters for their valve clearances, but the specifics are purely for this motorcycle.
With bucket and shim adjusters there is a shim that sits on top of the valve stem, with a closed cylinder bucket over the shim and valve springs with the closed end of the bucket being where the cam lobe presses to open and close the valve.
They are very accurate and tend to stay in adjustment for extended use. Mostly they need to be checked every 16,000 miles or so, and often do not need to be changed.
The clearance gap changes over time because of wear. Usually the wear is the valves at the valve seats, this can be exacerbated by poor quality fuel. Although the wear could be the shim, the valve stem, the bucket or the cam lobe, if these items wear it could be due to an oiling problem.
Honda CBR900RR Valve Adjustment
The Honda Fireblade engine is a high performance unit that revs to 11,000 rpm. It has double overhead camshafts and four valves per cylinder. It requires regular oil changes to ensure a long life for the engine.
The valve clearances need to be checked and if out of spec adjusted every 16,000 miles. Although there are a lot of steps to completing the job, the main issue for a home mechanic will be access to a set of shims, and having the correct tools. I recommend buying a set of shims, but it is possible to order the specific shims from Honda, but this will probably cause a delay in completing the job if adjustment is required.
The valve shim kits come in .05mm increments whereas if you are buying specific ones from Honda they will be available in 0.025mm increments. 0.025mm is very close to 1 thousand of an inch. In practice either type of shim is completely acceptable to make sure that the clearances are in the specified range.
Required Tools For DIY Mechanics
Here is a list of tools you will need to follow my method for motorcycle valve adjustment.
- Metric Imperial Feeler Gauge like these: https://ebay.us/qRyu99
- Sockets and spanners in the common mm sizes
- A torque wrench, with 12 newton metres within its range like this: https://ebay.us/z2oe9X
- Cam tensioner locking tool (mechanics stopper tool), this can be made or a small flat screwdriver and vice wrench can be used
- Vernier calliper, or micrometre
- A Magnet
- And of course, valve shims to do the job. These are the ones I used: https://ebay.us/Q6a3MD
Steps To Check Valve Clearance Motorcycle
- Remove the fairing middle sections and lower section
- Remove the fuel tank
- Remove the airbox
- Remove the coils
- Unbolt the radiator from the frame but there is no need to drain it
- Remove the valve cover by undoing the 6 10mm bolts
- Remove the circular timing cover
- Use the cam tensioner tool to take the tension off the cam chain, turn the tool clockwise and lock it
- Check the timing marks, I had to mark my pulse rotor because it didn’t have the factory marks.
How To Check Valve Clearance
First, set the engine at top dead centre for the 1st and 3rd cylinders taking the following into account. The cam sprocket is marked IN for intake and EX for exhaust.
Turn the engine over clockwise using the 14mm bolt exposed by the timing cover
If your pulse rotor has factory marks align the T mark on the pulse rotor with the notch on the cover which is at the 2 o’clock position.
In my case I used the marks I had made which corresponded to the line at six o’clock on the factory marked rotor ( in the factory manual this line is used for all of the settings other than the first)
This should also make the line under the IN on the left cam sprocket should line up with the surface of the top of the head and the line under the EX on the right cam sprocket should also line up with the head.
If they don’t line up, move the engine through another full turn and check that they line up.
There are two cam lobes for each cylinder so there are two clearances to check.
To record the measurements it is best to create a table to write them down. See the image below of my handy motorcycle valve clearance chart.
The inlet valve clearance is specified as .005 to .007 of an inch. To measure them start with a .007 feeler gauge. It is usually easier to do both lobes for one cylinder at a time starting with the largest clearance.
If this goes into the gap between the cam lobe and the surface of the bucket, try the next size up .008 and larger if it still goes in..
If it doesn’t fit go to the next size down, .006. Repeat this until you find one that fits.
The feeler gauge should go into the gap without force, and should give a slight drag as it is moved in and out.
Once you have found the correct feeler gauges for each lobe for both cylinders, record sizes on the table. The next pair of clearances to check are the exhaust valves for cylinders 2 and 4.
The engine needs to be moved forwards by 180 degrees clockwise. This time the single mark that was previously at 6 o’clock will have moved to 12 o’clock.
The exhaust valve clearance is specified as .007 to .010 of an inch for 95 to 96 engines, and .009 to .011 for 97 to 98 engines. Start with the largest size feeler gauge .010 or .011 depending on the motorcycle’s manufacture year.
Go through the same process of larger or smaller gauges as with the inlet until you have found the right sizes and recorded them in the table.
The next set are the inlet valves for cylinders 2 and 4. To set these, move the engine 180 degrees forward until the marker has gone back to 6 o’clock. Check the clearances and record them.
Finally move the engine through a further 180 degrees until the marker is back to 12 o’clock then check the clearances for exhaust valves on cylinders 1 and 3 and record them.
Once you have measured all 16 clearances check the clearances you have measured against the specification to see if any need to be adjusted.
If they are all within the specified range replace the parts that you removed.
How To Adjust Valve Clearance
First set the engine as if to check the clearances, ie back to top dead centre for the 1st and 3rd cylinders taking the notes in the clearance section into account. Removing the cams is actually quite easy.
Remove the cam chain guide from the cam chain end of the cylinder head. Undo the cam cover locking bolts in small steps following the numbers marked on the cover, they are marked 1 to 10 from the outside of the cover.
Be careful doing this as if you release them unevenly you could crack a cover.
Remove the cam covers, they may not release easily, a little persuasion with a wooden drift and a hammer may be needed. Remove the cams by unhooking them from the chain.
Now the specific buckets and shims for the valves to be adjusted can be removed. I recommend that you do this one at a time, or keep a very careful check to ensure that the buckets go back to the same slots.
Use a magnet to remove the buckets, usually the shim will come with the bucket, but occasionally the shim will stay sat on the top of the valve stem. If so, use a magnet to remove the shim, be careful not to drop a shim into an oilway.
The shims have their size marked from the factory, but sometimes the size is indistinct due to slight wear. Either way use a vernier or micrometre to measure them.
To adjust the clearance the shim needs to be changed for a new one. There is a calculation to work out the new shim size but it is easier to use this method.
For every thou (thousands of an inch) of clearance to be changed add or subtract .025 from the shim size. Add to reduce the clearance, subtract to increase.
Always aim for the middle of the range, but accept that due to the different steps in shim sizes you may be slightly one way or the other within the specified range.
For the inlet you should aim for 6 thou, but if you end up with 5 or 7 that would be fine. Personally I would always go for more clearance than less if there is a choice, but it shouldn’t really matter.
For example if you want to increase the clearance by 3 thou subtract .075 from the shim size. If the shim was 2.10 the adjusted size would be 2.025. This size can be ordered from Honda, but if you have a kit you would go to the nearest size that would keep the clearance within the specified range. This would be a 2.05, although it would give you one thou less clearance it will keep you within the range.
Once you have replaced the appropriate shims, replace the cams, ensuring that the TDC marker hasn’t moved, and that the IN and EX marks are parallel to the head surface. This may take a couple of attempts but it is important to get it right.
Replace the cam covers. Tighten them following the numbered sequence in small steps. You may have to overcome some of the cam lobes pressing against valve springs so be careful and methodical. Then torque them in two steps to finish at 12 newton metres, which is quite low so do not get carried away with the initial tightening.
Now turn the engine over at least 2 times using a socket on the end of the crank. Take this slowly just in case you didn’t get the cam timing right. Any resistance should be investigated without using force.
Then set the engine for checking the motorcycle valve clearances, then check them all again. Having removed and replaced the camshafts can cause a little variation on clearances, besides the ones you have already changed.
If you find any of the remeasured values out of spec you will have to go through the adjustment stage again. This doesn’t usually happen, but can occasionally, which can be annoying!
Once all of the measurements are within the specified range then put everything back together in this order:
- Remove the cam tensioner tool
- Replace the circular timing cover
- Replace the valve cover 6 x 10mm bolts torqued to 12 Newton Metres in 2 steps
- Refasten the radiator
- Replace the coils
- Replace the airbox
- Replace the fairing middle sections
- Replace the tank
The valve shims that are used to set motorcycle valve clearance mean that the adjustment will stay in spec for much longer, than the old style screw and lock nut adjustment older bikes have. There is no need to run them in, you can use the engine performance in full straight away, once up to temperature of course.
Honda CBR900RR Fireblade Valve Clearance Guide On YouTube
Once you have set the motorcycle valve clearances they should be good until the next time they are due to be checked and as long as the bike is serviced regularly they are very unlikely to change. Obviously if the engine is used for racing you will have to change your service intervals to take into account the extreme use.