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This maintenance tutorial addresses TT250 valve adjustment.

You’ll need the following tools for this operation:

• A pair of pliers
• 14mm socket with ratchet and extension
• Spark plug wrench
• 10mm wrench
• Long handled Phillips head screwdriver
• Large bladed flat head screwdriver
• 6mm Allen wrench

The TT250 has a two-valve engine.  The intake valve opens to admit the fuel/air mixture, and the exhaust valve opens to expel the exhaust.   When the engine is at the top of its compression stroke, we want both valves closed.   That’s because we want to compress the fuel air mixture, ignite it, and then allow the resulting high combustion pressures to drive the piston down.   If any leakage occurs around any of the valves while this is occurring, the engine will lose power and it could “burn” a valve if the combusting fuel/air mix escapes around the valve while it is still burning.

When engineers design an engine, they want it to do the above, but they have to account for the thermal expansion that occurs as engine temperature increases during normal operation.  In order to compensate for this thermal expansion, the engineers design in a gap in the rocker arm/valve train.   As the engine warms, this gap approaches zero, and everything works the way it is supposed to.

On the TT250, the valve train looks like you see in the photo below (this photo shows the exhaust valve, but both the intake and the exhaust valve have similar valve trains).   The valve gap (also referred to as the valve clearance) is what the lower red arrow points to in the photo below.

As the wear described above increases, it has the effect of reducing the valve gap (i.e., the clearance built into the valve train to account for the thermal expansion as the engine warms up).   What happens is that as this wear occurs, the valve actually moves higher into the cylinder head and the valve gap decreases.   If this wear goes beyond acceptable limits without adjusting the valves, the valve gap grows smaller and smaller.  Ultimately, this wear will result in the valve being held off the seat when combustion occurs.   This is bad, because when this condition exists, hot burning gases escape around the valve sealing area.  Ultimately, these burning gases will destroy the valve and the seat.   That’s what happens when we “burn a valve.”   It’s also bad because the valve needs to cool, and it is cooled primarily when it is closed against the valve seat.   That allows heat to escape from the valve and flow into the cylinder head.  If the valve never fully closes, the valve will continue to heat, and the valve stem will expand diametrically so much that it seizes in the valve guide.   That’s really bad, too, because when that happens, the valve will stick, the piston will hit it, and you’ve just bought yourself a new engine (or you’ll have to pay for expensive repairs on the current engine).

If the above sounds really bad, relax.  We avoid it by adjusting the valves.  All we are really doing is keeping the gap in the valve train within an acceptable range over the life of an engine.  As the valve and the valve seat wear, we keep everything adjusted so that when the engine is at operating temperature we still form a good seal around the valve seat.   That’s the whole idea behind this valve adjustment business.

Different engines use different approaches for adjusting the valves.   Your TT250 engine uses the best approach for easy maintenance and high performance:  It uses a threaded adjustor shaft with a lock nut to set and lock the valve gap.   In the photo above, that’s what the upper two arrows point to.  These adjustors are located in the ends of the rocker arms that interface directly with the valve stem.

So, with all that theory behind us, let’s consider what we’re going to do here:

1. We want to gain access to the valve rocker arms and their adjustment screws.
2. We want the engine to be at a point in its rotation such that the rocker arm is on the cam’s base circle.  This means the cam is not actuating the rocker arm.   We want the engine to have the piston at (or very near) top dead center, which means the valves should be closed (which is another way of saying the rocker arm is on the cam’s base circle).
3. With the engine in this position, we want to loosen the threaded adjustor lock nuts, we want to set the valve gaps to the specified gap of 0.04mm to 0.07mm, and we want to tighten the lock nuts to lock the threaded adjustors at this gap.  We always make the adjustment to the 0.07mm setting.  As the valve and the cylinder head wear, the gap will grow smaller.   Setting it to the 0.07mm setting allows us to keep the valve adjustment interval (the number of miles you can ride between valve adjustments) at a reasonably high number.   Initially, we’re establishing this interval to be 500 miles for the first adjustment, and every 2500 miles thereafter.
4. When we’ve completed the above, we want to put everything back together.

Got that?   Okay, here we go….

Most of the work in adjusting the valves is associated with just getting access to the adjustors.   The adjustment operation (once we have access) takes only a few minutes.

When you adjust the valves, you have to start with a cold engine.  Dead cold.   Let your TT250 cool down completely.    Don’t cheat on this part.   I always let the bike set, without starting the engine, for a day.   If it’s even a bit warm from running, your adjustment will be wrong, and all of your work will be for nothing.  Let your TT250 cool down completely.

Remove the rear body panels on the left and right side of the motorcycle.

Remove the seat.  It’s secured by 10mm bolts on either side.  Once the bolts have been removed, the seat slides to the rear.

Close the fuel petcock and remove the fuel hose from it.

Remove the hose from the right upper hose boss on the carbon canister.   The other end of this hose remains attached to the fuel tank.

Remove the 10mm bolt at the base of the fuel tank.  You’ll see it after you have removed the seat.

Remove the two screws that secure the left and right fuel tank body panels to the frame.   You do not need to remove the body panels from the fuel tank.

Slide the fuel tank to the rear.  After you have lifted it partially off the motorcycle, disconnect the electrical connector that runs from the fuel tank sending unit to the fuel gage.

When you remove the fuel tank from the motorcycle, two hoses will hang down.  The longer one is the fuel tank overflow line.  It simply hangs down from the fuel tank; the other end is not attached to anything (it vents to atmosphere).   The shorter hose is the one that attaches to the carbon canister.  You’ll have to reinstall the end of it on the carbon canister boss when you reinstall the fuel tank after adjusting the valves.

At this point, we have what we want, and that’s access to the valve cover.

The valve cover is attached to the cylinder head by three 10mm bolts.  Note that there is a fourth 10mm bolt on top of the valve cover (it’s the one in the photo below just beneath and partially behind the hose).   Leave that bolt alone (do not remove it from the valve cover).   Do remove the three bolts that attach the valve cover to the cylinder head.

Detach the large diameter hose from the exhaust gas recirculation valve shown below.

Tap the valve cover gently to break the seal between it and the cylinder head.

Remove the valve cover.   It will remove to the right side of the motorcycle.

The valve cover seals to the cylinder head with an o-ring type seal.   Place the valve cover where this seal will not be contaminated by dirt or debris.  Prior to reinstalling the valve cover (after you have adjusted the valves), apply a light coat of motor oil to the rubber seal.

Remove the spark plug.

Remove the left crankcase engine cover.  It is secured with three Phillips head screws.

After you have removed the cover, you will see a 14mm bolt head.  By placing a socket wrench on this bolt head, you will be able to rotate the engine (it’s why we removed the spark plug).   If you have the bike in the vertical position (straight up and down), only a tiny amount of oil will escape.   If the bike is on the sidestand, more oil will escape.

Remove the timing port cover on the left side of the engine with a large blade screwdriver or a coin.

When you remove the timing port cover, take care not to lose the o-ring that seals it.  Place the o-ring in an area where it will not become contaminated with dirt or debris.

Rotate the engine by hand by attaching a 14mm drive to the crank bolt.

There are three timing marks on the crank shaft indicator wheel.  One is a double scribe line that shows when the ignition is fully advanced.  We’re not interested in that one for the valve adjustment operation; this information is included here for reference only.

The next mark is a scribe line with an F.  This shows when the spark plug fires.   We’re not interested in that mark, either, for the valve adjustment operation.  It’s mentioned here for reference only.

Here’s the mark we’re interested in.  It’s a scribe line with a T.   That shows when the piston is at top dead center, which is where we want it to be for the valve adjustment operation.

This business of aligning the T mark and its scribe with the slot in the threaded area is a little tricky.   You should manually rotate the engine so that this T mark and the scribe line are aligned with the slot and both valves are fully closed.    Rotate the engine’s crankshaft through the full 360 degrees at least twice to understand what it going on here.   On one rotation, you may see that one of the valves is not fully closed.   If that’s the case, DO NOT adjust the valves with the engine crankshaft in this position.  Rotate the engine another 360 degrees to bring the T mark and scribe line into alignment with the slot in the threaded area.   Both valves should be fully closed, which is to say that the rockers should be in the full up position and the valve gap is fully open for the both valves.

Once the engine is at top dead center as described above, we’re ready to make the adjustment.  We’ll do so by loosening the 10mm nut (shown by the middle arrow in the photo below) enough to allow us to rotate the threaded adjustor (shown by the upper arrow in the photo below).   By doing this, we are changing the valve gap (shown by the lower arrow in the photo below).

Loosen the threaded adjustor enough to allow insertion of a 0.07mm feeler gage into the valve gap, as shown below.

Hand tighten the adjustor so that it is snug against the feeler.  You don’t want to overtighten the adjustor or you will start to open the valve and your adjustment will be incorrect.   Just make it snug so that if you try to pull the feeler out, you feel slight resistance.   Tighten the 10mm adjustor lock nut.

Repeat the above process for the other valve.

After I’ve done this, I manually rotate the engine two complete revolutions, align the T mark and the scribe line again, and check the clearance just to make sure I did it correctly.

Assembly is the reverse of disassembly.

Once you’ve reassembled the motorcycle, go out and put some miles on it!

The maintenance tutorial addresses TT250 front wheel removal and installation.

You will need 15mm, 17mm, and 10mm wrenches for this operation.

Start by securing the motorcycle on a lift such that the front wheel is off the ground.

Unbolt the front brake caliper by removing the two 10mm bolts that secure it to the front fork.  Allow the caliper to hang by the hydraulic brake line.  Do not loosen or remove the hydraulic brake line.

Loosen the front axle by using a 17mm wrench on the axle nut and a 15mm wrench on the axle’s bolt head.

This is the right side of the motorcycle showing the 17mm axle nut.

This is the left side of the motorcycle showing the 15mm axle bolt head.

Remove the axle nut.

Pull the axle out of the forks.

There is a bushing between the left side of the front hub and the left fork.  There is no bushing on the right side of the motorcycle.  The speedometer drive mechanism is on the right side of the motorcycle.  It is located between the right fork and the right side of the hub.

Front wheel installation is the reverse of front wheel removal.

Prior to installing the speedometer drive mechanism, it is best to disconnect the speedometer cable.   You should apply grease to the inside of the speedometer drive mechanism and the right side of the wheel hub.   Note that the speedometer drive mechanism has two tabs.   Take care to align these with the front hub slots when installing the front wheel.

Reinstall the front axle, the front axle nut, the front brake caliper, and the speedometer drive cable.   The front axle should be torqued to 35 ft-lbs.  The caliper bolts should be torqued to 22 ft-lbs.

Check the front brake prior to riding to assure proper operation, and you are ready to ride.

This maintenance tutorial addresses adjusting the TT250 motorcycle’s chain and aligning the rear wheel.  You will need 13mm, 18mm, and 19mm wrenches, and a screwdriver for this maintenance activity.

You don’t have to get the rear wheel off the ground to adjust the TT250’s chain.   We had the rear wheel elevated in this tutorial to make the photography easier.  We do chain adjustments all the time with the motorcycles on their sidestands.

When the chain is properly adjusted, it should have about 15mm (or 3/5 of an inch) slack at its midpoint.

You can check this adjustment easily, and you should perform this check on a regular basis.   On long rides, we check and lube our chains every day when we are out on the road.  After you’ve done this a few times, you can adjust your chain in about 3 minutes.  A lubricated chain will require adjustment every 500 to 1000 miles once the motorcycle is broken in.

Adjusting the chain involves loosening (but not removing) the rear axle, loosening the adjustor nuts and lockuts, using a screwdriver between the chain and the rear sprocket to remove all kinks, aligning the rear wheel, tightening the rear axle, and tightening the adjustor nuts and locknuts.

The rear axle is loosed by loosening the rear axle bolt and nut.  The rear axle bolt head on the right side of the motorcycle takes an 18mm wrench; the rear axle nut on the left side of the motorcycle takes a 19mm wrench.  If your chain requires adjustment, loosen the rear axle.

Here’s the left side of the rear axle.

The rear axle adjustor nuts and locknuts are located behind the adjustor plate on both sides of the swingarm.  These are 13mm nuts.   Loosen both nuts on both sides of the swingarm.

The intent is to position and align the rear wheel such that the chain has 3/5 of an inch slack at its midpoint.   This is the amount of slack the chain should have with the motorcycle on the ground and the rider on the bike.   If the bike is on a lift such that the rear wheel is off the ground, you should increase the amount of slack when you adjust the chain such that when you are on the bike, the slack is 3/5 of an inch.

If the rear wheel must move forward to increase chain slack, back off on the adjustor nuts and locknuts and manually push the rear wheel forward.  If the rear wheel must move rearward to decrease chain slack, tighten the inner nuts as required on both sides of the swingarm to move the axle to the rear.

After moving the rear wheel, put a screwdriver between the chain and the rear wheel sprocket (as shown below) and sharply rotate the rear wheel.  This will remove any kinks in the chain.

Check the alignment of the rear wheel by comparing the scribe marks on the rear axle adjustors with the scribe marks on the swingarm.  You can see these in the photos below.

When we adjust the chain, we don’t fully unbolt the rear axle.  We just loosen it and use the adjustor nuts to drag the wheel to its required location.

When the rear wheel is aligned and the chain slack is correct, tighten the rear axle to 35 ft-lb.   Tighten the rear axle adjustors’ 13mm positioning nuts, and then tighten the rear axle adjustors’ locknuts (the outer 13mm nuts) to lock the adjustors in place.

We always lube the chain every time we adjust it.  You can use either a wax-based or an oil-based chain lube; we stock both types.  You can call us at 909 445 0900 if you need chain lube.

That’s it.   You are ready to ride!

This tutorial addresses TT250 front and rear brake maintenance.

General Information

The front brake master cylinder is located on the right handlebar.  It has a fluid level indicator on the master cylinder that shows the “low” level.  When the front master cylinder fluid level is at the low mark, it is an indication that the front brake pads should be replaced.   Do not rely only on this indication; you should check the pad thickness regularly and replace them when they are worn below acceptable limits (to be described below).

The rear brake master cylinder is located under the seat and behind the carburetor.   It is visible from the right side of the motorcycle, but it is easier to check the brake fluid level if the left rear body panel is removed.   The left rear body panel is secured by a screw and two grommet snaps, as shown in the photos below.

This is the rear master cylinder.  Note the upper and lower fluid level marks.

It is possible to check the thickness on the front and rear brake pads without removing the caliper from the motorcycle, but you have to get below the brake calipers to do so.  It is better to remove the caliper to better see the pads.

Front Brake Pad Inspection and Replacement

The front brake caliper is located on the left side of the motorcycle.

Loosen the front brake caliper’s two 5mm Allen pins.

Remove the caliper’s two 8mm mounting bolts and then remove the caliper from the front rotor and fork.   You should not remove the hydraulic brake line or loosen it.

Completely remove the caliper’s two 5mm Allen pins, and remove the two brake pads.

The front brake’s pads are interchangeable left to right (the rear brake’s pads are not).  Note that the brake pads have wear grooves machined into the pad surface.   These are the three vertical slots you see in the photo above.  When the pads are worn on either pad such that the wear indicators are no longer visible, replace the pads with new pads.   We keep these in stock, so call us at 909 445 0900 if you need to order a pair.  Note that it is normal for the front brake pads to wear much more quickly than the rear brake pads.

Push the caliper pistons all the way into the caliper.

Assembly is the reverse of disassembly.  Install new front pads , install the two 5mm Allen pins, place the caliper over the rotor, and install the two caliper mounting bolts.  The 5mm Allen pins should be torqued to 3 to 5 ft-lbs.  The caliper mounting bolts should be torqued to 15 to 18 ft-lbs.

Rear Brake Pad Inspection and Replacement

The rear brake caliper is located on the right side of the swingarm.

Loosen the rear brake caliper’s two  5mm Allen pins.

Remove the caliper’s two 8mm mounting bolts and then remove the caliper from the swingarm.   You should not remove the hydraulic brake line or loosen it.

Completely remove the caliper’s two 5mm Allen pins, and remove the two brake pads.

Note that unlike the front brake, the rear brake’s calipers are different.  The one with the extension on it goes on the inside of the rotor (the side closest to the spokes).

When the pads are worn on either side such that the wear indicators are no longer visible, replace the pads with new pads.   We keep these in stock, so call us at 909 445 0900 if you need to order a pair.  Note that it is normal for the front brake pads to wear much more quickly than the rear brake pads.

Assembly is the reverse of disassembly.  Push the caliper pistons all the into the caliper.  Install new rear brake pads , install the two 5mm Allen pins, place the caliper over the rotor, and install the two caliper mounting bolts.  The 5mm Allen pins should be torqued to 3 to 5 ft-lbs.  The caliper mounting bolts should be torqued to 15 to 18 ft-lbs.

Front and Rear Brake Rotor Inspection

Both the front brake and rear brake rotors are 4mm thick when new.  If either rotor thickness drops below 3mm, the rotor should be replaced.

The front and rear brake rotors are each retained by Allen head bolts that take a 6mm drive.   These should be torqued to 22 ft-lbs.   Take care when removing these for the first time; they are Loctited in place at the factory and it is easy to strip the Allen drive socket (we recommend heating the head of the bolt first to soften the adhesive).  We keep replacement rotors in stock; if you need a new rotor please call us at 909 445 0900.

Flushing and Replacing the Brake Fluid

It is a good idea to bleed the brakes every year, and to flush and replace the brake fluid every two years.  Use only DOT4 brake fluid.  We sell brake fluid suitable for use in your TT250 motorcycle; if you need brake fluid please call us at 909 445 0900.

To drain the brakes, open the master cylinder.   Attach a hose to the caliper bleed port and route it to a suitable container.  Open the caliper bleed port with an 8mm wrench and allow the brake fluid to drain.  Note that the drain hose is not shown in the photo below to allow clarity in identifying the caliper bleed port.

After draining the brake fluid, add fluid to the master cylinder and bleed the brakes as described below.

Bleeding the Brakes

To bleed the brakes, attach a hose to the brake caliper bleed port and route it to a suitable container.

Open the master cylinder.  The front brake master cylinder cover is removed with a Philips head screwdriver.   On the rear brake master cylinder, it is best to gain access by removing the left rear body panel (as outlined earlier in this maintenance tutorial), unbolting the master cylinder from the frame, and temporarily securing the rear brake master cylinder in a vertical orientation with a zip tie.

Open the caliper bleed port with an 8mm wrench while applying the brake lever, and before releasing the brake lever, close the bleed port with the 8mm wrench.  It’s important not to allow the bleed port to remain open while releasing the brake lever or you will suck air into the system.   Repeat this open-the-bleed-port, apply-the-brake-lever, close-the-bleed-port, add-brake-fluid process until the master cylinder is full.   Reinstall the brake master cylinder cover.   For the rear brake master cylinder, reinstall the rear brake master cylinder in its proper location and reinstall the left rear body panel.

Prior to taking the motorcycle on the street, operate it slowly and apply the brakes several times.  Once the system is appropriately pressurized, you’re ready to ride!