Valve clearance adjustment is required at regular intervals. My manual specifies checking every 10,000 Km6,000 Miles. For me, checking and, when necessary, adjusting is the most technically challenging thing I’ve done. For that same reason, it’s the most satisfying, and the most money-saving.
This job takes a long time — allow 4 to 8 hours, with a trip to the shop at the halfway point.
Perhaps that needs clarification. This job took me 4 to 8 hours and, if you have never done this kind of thing before, it will probably take you that long. Maybe a little less, because I was pausing to take pictures. No doubt experienced mechanics can do it in a hour, with one hand, while grooming their dog with the other.
- Rear stand (recommended)
- Factory service manual or 3rd-party manual such as the Klymer (there are too many critical specifications to go without, and I can’t promise yours will be the same as mine. Get the manual, and use my description here just to help you understand the steps).
- Phillips screwdrivers
- Hex wrenches
- Metric sockets.
- Torque wrench
- Feeler gauges in the appropriate range. As much graduation as you can get in the 0.1mm — 0.3mm range is what you are looking for.
- Micrometer (not actually required; in theory you can do the calculations with the shim-type code marked on the shim, and the shim substitution table in your service manual. I prefer to measure and do the subtraction myself.)
- Replacement shims (but you need to do half the job before you know how many or what sizes)
- Possibly a valve cover gasket (with care you can reuse the old one but I keep a new one on hand just in case)
- RTV silicone sealant
Difficulties & Warnings
Some difficulties could be:
- It takes a long time because of the number of steps and the amount of disassembly required. Also, because you must do a bunch of work before you know the details of a part (replacement shims) you need, it requires a trip to the motorcycle shop mid-job, so you probably are forced to take at least two days to do it. Or, you can buy a complete set of shims — one of each size — in advance (about $75 on eBay) to improve your chances of already having what you need.
- Also, check if your bike shop keeps shims in stock. If they have to order them for you, your bike will be out of commission while you await the order. Usually they have a complete set in the service department and will, if you ask politely, sell you stock from their service set. Some shops will also take your old shims in trade.
- Lots of opportunities to drop small parts into dark corners
- Correct torque of engine bolts is critical
- Correct re-installation and alignment of cam chain is critical (only done if actual shim adjustment is needed, not for just checking clearances)
Unfortunately the time I took these photos the valves were in-spec, so no adjustment was required, so this article only covers checking the clearances, not adjusting them. Next time I will probably have to adjust, will take photos, and will fill out that part of the procedure. Meanwhile, there is a reference below to the adjustment procedure for another bike.
First you must
Since this job involves removing a lot of small parts, I like to have a divided parts box on hand, and place the parts in it, in order, as they come off. The 6 screws involved in removing the seat go in the first compartment, then the 4 for the gas tank go in the second compartment, etc.
This makes it far easier to ensure that all the parts go back where they belong and in the right order.
Now the hard part — getting the cover out of there. You must lift the left side and remove the cover out the left side of the bike. You have to lift it as high as possible before pulling it out, so the cover clears the cam timing chain and wheel on the left side of the engine.
You will be sure it doesn’t fit and you’ll need to struggle with various angles for a while. Pressing the nearby radiator hose out of the way may help.
If it is undamaged, you can carefully clean the old silicon off it and use it again. If it is broken or torn you will have to replace it.
For your first time doing this job, you may prefer the confidence of spending the $10 and putting in a new one. (I keep a new one on hand just in case, but haven’t had to use it.)
Standing on the right side of the bike, look into the engine. You can see 4 pear-shaped cams of highly polished metal. Each one presses down on a shim, and on a valve, or releases it, as the cam shaft rotates. The shims are the dull gray disks the size of a Canadian Loonie immediately under the cams. There is one visible under the bottom left cam in this photo.
The two cams toward the rear of the bike (on the left in this photo) are over the intake valves, while the two toward the front are for the exhaust valves.
You will be measuring the clearance between each cam and the shim underneath it.
The cams need to be in specific rotation positions for this measurement. In this photo they are pointing in various random directions, whereever the last use of the engine happened to leave them. This won’t do. Next we will rotate the engine and the cams to exactly the right position for measurement.
The upper one (circled in red here) reveals a rotating disk with some reference marks, called timing marks, engraved on it.
The lower one (circled in green here) reveals a large hex bolt head that can be used to rotate the engine counterclockwise.
Fit a socket to the rotation bolt and gently rotate the engine counter-clockwise while looking through the inspection window.
Only turn the engine counter-clockwise. If you overshoot a timing mark, go around another time, don’t try to back up.
You will see various engraved marks go by. Stop when a line, and the letter “T”, lying on its side, are centred in the window. Click the photo to the right for a large version to see what this looks like.
The “T” is for “Top Dead Centre” and indicates the piston is at the exact top of the engine. This also means all the valves will be fully open, which is what we want.
Unfortunately, my photo of the actual measurement of clearances was spoiled by carelessness. Next time I do this I’ll fill in this photo. Sorry about that.
But what you do is measure the clearance between each cam and the shim underneath it by sliding various sizes of feeler gauges into the gap, looking for one that fits with some resistance.
Here is a photo of doing this on a different bike (a ZX-6R).
It’s easier on the KLR because there is much more space to work in.
Check all 4 valves (2 intake, 2 exhaust) and write down the clearances, carefully recording which one went with which valve. Here is the table I wrote down doing this check just now.
The manual says that the clearances should be 0.10 to 0.20 mm on the intake side and 0.15 to 0.25 mm on the exhaust side, so the numbers measured here are in spec — no adjustment is required.
|Intake||0.12 mm||0.11 mm|
|Exhaust||0.16 mm||0.20 mm|
|Intake||0.10 to 0.20 mm|
|Exhaust||0.15 to 0.25 mm|
If any adjustment was necessary, we would do it here.
Next time I do this service I expect I’ll have to do adjustment, and will document it here. Briefly, the steps are:
- For each valve whose clearance is out of spec, calculate the different shim size that would put it in spec. (Calculate how much out of spec the gap is, measure the thickness of the current shim, add or subtract the deviation to calculate what size the shim should be)
- You can do this by measurement and math. Just measure the thickness of the shim with a micrometer. A thinner shim will make the gap bigger, and a thicker shim will make the gap smaller.
- Or, your service manual will contain a table in which you can look up the current gap size and the code stamped on the shim, and it will tell you what new shim you need. Personally I find that a very complex way to avoid subtracting two numbers, and I prefer to just measure and subtract.
- Buy replacement shims of the needed sizes (or take them out of the set you already have on hand).
- Remove the cam shafts, getting access to the shims (also involves removing the cam chain and the cam chain tensioner).
- Replace the out-of-spec shims with the new ones.
- Replace the cams shafts (also involves re-installing and resetting the cam chain and the cam chain tensioner).
It’s not hard, although it takes a bit of time, and the re-installation and re-synchronization of the cam chain can be a little intimidating until you have done it once.
For now, here is a link to doing this procedure on a different bike (harder) just to give the general idea.
Having checked, and possibly adjusted, the valve clearances, we now need to reassemble the valve cover.Using a fingernail or a soft tool like a piece of plastic or a popsicle stick, carefully clean off any old silicon sealant that may be stuck to the rim around the engine casing. Also wipe away any oil or grit, leaving a clean flat surface.
Carefully install the gasket on the engine head, making sure it is perfectly lined up with the edges all around, and pressing gently down so the sealant grabs hold. Make especially sure that the sealant has sealed the half-moons into the half-moon-shaped depressions in the head.
If possible, take a break for a few minutes to give the adhesive time to grab hold.
Now we’ll replace the cover bolts.
You might not have noticed, when you removed them, that they are not all the same. Two are longer.
The shorter two go on the left side, adjacent to the raised part of the cover where the cam chain is.
Put the bolts in place and snug them up, then use a torque wrench to bring them to the specified torque.
My manual calls for 8 Newton-Metres71 inch-pounds. That’s not very tight — if you’re doing this by hand without a torque wrench (which you should not be) it’s just a bit more than snug with a socket wrench.
That’s it. The rest of the reassembly is just a careful reversal of the disassembly steps: put all the bits back in place around the engine head, then reinstall the gas tank, seat, and fairings.
(While you still have the gas tank off would be a great time to remove and service the spark plug, if that is on your to-do list.)
As soon as possible, test-run the engine and carefully check for oil leaks around the valve cover gasket. The most common problem with this procedure is that if the gasket is not installed flat and clean and well-aligned, oil will leak out around it. It’s not subtle — if you have it wrong you’ll know quickly because the oil will trickle over the hot exhaust header and smoke.
That was a pleasant afternoon, and a saving of a couple of hundred dollars. Thanks for following along with me.