TTR250 Valve clearance checking and adjustment

DISCLAIMER: The modifications described in the following text are for educational purposes only. In no way do I recommend that you apply these modifications to your own motorcycle. If you do choose to go ahead and modify your motorcycle based on the information in this document you will accept all responsibility for your own actions. The author(s) of this document, and host(s) providing it for you, accept no responsibility whatsoever. If you are unqualified to make any of the changes described herein but are bent on doing the modification, seek out a knowledgeable friend or professional mechanic for assistance.


Valve clearance checking and adjustment.


NOTE: This is just a guide; it does not replace a service manual, general mechanical knowledge, specific motorcycle repair experience and good old common sense. With the proper tools, some general experience and this guide most users will be able to successfully check valve clearances and if required replace shims to adjust the valves to service specifications. If you have any problems then stop and ask questions on the forum, take pictures of your point of confusion and get your answers before you start.

Basic hand tools, all metric
3/8 Drive socket set, 10mm to 17mm
Allen key set 5mm to 15mm
Spanners 10mm to 17mm
Feeler gauge set that covers up to .30mm
Magnet on a stick
Digital camera
Pen and paper

You will be taking pictures, writing notes, removing the seat, tank, the timing sight plug on the left cover, the crank access plug on that same cover. Spark plug and valve cover. If adjustments are needed, removing the cam chain tensioner  and cam caps. Measuring the clearance between the bucket and cam, reading a very faint number printed on the valve shim, or better yet measuring it with a micrometer. This list is not all inclusive, as stated its basic so if what is shown above is beyond what your comfortable doing then stop and ask for help. 

The e
ngine should be cool to the touch prior to starting the valve check.

Before you start, remove the seat and petrol tank and power wash the area above the cylinder head so that no dirt can drop into the engine when it is being dismantled.

Then make sure that the bike is safely on a stand and at a comfortable working height - if at all possible. Make sure the floor and working area is clean. I tend to rob the recycling bin of old newspapers and lay them around to give a clean absorbent surface on which to put down any parts removed.


Next remove the three Allen bolts and take off the cam cover being careful not to damage the rubber gasket.

Take out the timing access plug. No kick start on this TTR so I put the engine in 6th gear and turned it to the TDC mark using the rear wheel. TDC is the SINGLE mark and not the H shaped mark about half an inch away.

Ensure  the alignment markers and both cam lobes are pointing away from each other as shown in the pics below.

The engine is at TDC on compression stroke now and you can check the valve clearances.

Take a quick look at the timing mark, and make sure the crank has not rotated and the index line is still in the centre of the sight window (this is a repetitive step, but key to getting good readings off valves).

I use a laminated guide with the cam lobe positions and clearance ranges written on it along with an essential bit of kit - a set of metric feeler gauges with individual gauges from 0.02mm to 0.10mm and then in stages of 0.05mm. Stack two blades where necessary.

The OEM service limits for clearance is:
Intake 0.09mm ~ 0.19mm
Exhaust 0.19 ~ 0.27mm

So starting with any valve and bucket, pick the feeler gauge blade of the minimum service limit and see if it fits cleanly, without force between the shim bucket and the cam face.


Starting with an intake valve try a 0.10mm blade, if it does not fit in, your clearances are too tight. Go to the next size down blade in your feeler gauge set until you find one that fits, and write down the size. If the 0.10 blade fits, go up one size at a time until you get to a blade that does not fit. Write down the last blade size that fits.
Do so for the remaining three valves. Bottom line, your job here is to find the blade that fits the valve clearance gap, it should be a slight drag as you pull it though..

If your clearances are too small (below service limit) you will need a smaller (thinner) shim. Swapping to a thinner shim under the bucket will move the bucket farther away from the cam and increase your clearance.
If the clearance was too large (above the service limit) you will need a larger shim (thicker shim) In order to move the valve bucket closer to the cam face.

If your clearances are within the service limit. You’re done, put everything back together and go ride.

Remember as the valve face wears, they recede into the head and the valve clearances get smaller (less) So if you are measuring a clearance close to the minimum service limit,, consider adjusting them now.

Once the hard coating on the valve face starts to wear, the valve clearances will close up in just a few hours. You can adjust them again to service limits, but they will rapidly continue to wear. It’s time for a valve job.

Removing the Cams and Adjusting Valve Clearances

In order to remove the cams to gain access to the valve bucket and below it the shim, you will need to remove the cam chain tensioner.

Loosen the access bolt on the end of the tensioner whilst the tensioner is still fitted. Much easier than when the tensioner is off!

To keep the chain from falling down, use a long spring, piece of wire or zip tie to hold it up. If it falls free, no worry.. Just retrieve it with a hook before you turn the crank. It cannot fall so far down you cannot retrieve it; nor can it fall off the lower sprocket.

Then break loose each of the cam cap bolts working diagonally and remove them with their caps.

Once all eight cam cap fasteners are out, remove chain from the sprocket as you remove the cam. Set the cams aside in a protected location, clean and dust free as you can. Both camshafts have the same part number so the way to tell which goes where is to mark them as you take them off.

To save mess, I remove the oil that sits around the exhaust valves with a syringe.


The valve bucket is now accessible, remove it with a magnet or, as I do, use an old valve lapping tool (suction cup).

CAUTION: the small shim (9.48mm dia) may stick to the underside of the bucket, it may come part way out of the valve top, or it could stay in place.. Be careful it does not come off with the bucket and then drop free to be lost in the engine. Retrieving a shim from the engine is possible, but time consuming, and often requires further disassembly and or removal of the engine from the frame. Many hours may be lost doing this. So spending a few extra minutes to stuff clean lint free rags in the open parts of the head is well worth it till you understand what is happening.

What shim do I need to fix my clearances?

Now that you know what the clearance is for each valve, you have the shims out and know what size each is, and you know the service limits it's time to do some math and figure out what shim you need to install.

The OEM service limits for clearance are:
Intake 0.09mm ~ 0.19mm
Exhaust 0.19 ~ 0.27mm
Shims come in two types, The OEM has increments of 0.01mm (so you could have 181 or 186), and the aftermarket ones come in .05mm increments only. You can use either to correctly adjust the clearances.
The diameter of a TTR valve shim is 9.48mm.. and then the shim thickness is noted on the shim itself.. Typically they start at about 1.80mm and go up to 2.80mm or so. Normal shims used in a TTR are in the 1.90mm to 2.20mm. Less than 1.60 or so will often be so thin that the shim would be below the surface of the valve spring top causing the bucket to push down on the top and not the shim. This will damage the bucket, and often cause the valve colletts to come loose.

Here are some examples assuming you want the clearance to be in the middle of the spec. and you’re using an aftermarket shim from Hotcams

Intake valve, measured clearance of 0 .05mm
Valve shim is a 2.50mm
Service limit is 0.10mm to 0.20mm (you decide you want it in the middle of the spec at 0.15mm)
So you need increase the clearance .10mm
That means you need a 0.10mm THINNER shim.
If you install a 2.40mm shim you will end up with a clearance of 0.15mm. Your desired end state.

One more:
Exhaust valve, measured clearance of .25mm
Valve shim is a 2.85mm
Service limit is 0.20mm to 0.30mm (you decide you want it in the far end of the spec at 0.30mm)
So you need increase the clearance 0.05mm
That means you need a 0.05mm THINNER shim.
If you install a 2.80mm shim you will end up with a clearance of 0.30mm. Your desired end state.

You may find it easier to work from this chart:

Timing the cams

This is a very easy thing to do, but often misunderstood or over complicated.

Set the single timing mark in the centre of the window.
Pull up on the cam chain and install the intake cam with the sprocket timing marks close to the correct position lobes at 10 0’clock.
Install the exhaust cam with the timing marks roughly in their correct position and lobes pointing outward as shown in the earlier photo.
Stick your finger in the hole where the cam chain tensioner goes, and push against the timing chain guide to take up chain slack.. Check the flywheel timing mark and look at the cam timing marks..
Make note of which cam needs to roll forward or backward to get the timing correct. One at a time, remove the cam, lift the chain of the sprocket and rotate the cam, sit it back in the head and do the other.
Check flywheel timing mark again, push against the chain guide, check the cam timing marks. Adjust again if needed. If not, install the cam caps.
Reinstall the cam chain tensioner and it should look like this:


Cams in, caps tight, cam chain tensioner installed. Now turn the engine through one full cycle, until it is back on the compression stroke, flywheel timing mark centred in the window. CHECK the cam timing marks… check the flywheel timing mark, check the cam timing mark. Over kill?? Yes, but compared to destroying your engine because you skipped 30 seconds of checking a few timing marks several times - priceless! Verify your valve clearances. If you measured carefully, your notes were correct and maths was right, the clearances will be dead on where you wanted them. If so, put it all back together, and go ride. 

Job done!

Brian Sussex

Compiled by Brian Sussex, Devon, UK - everything you need (possibly!) for your TTR250 - all you ever wanted to know about TTR250s - the forum for TTR250 owners -
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