VW Polo 9N3 GTI, 1.8T BJX Engine - Timing Belt Replacement Guide

A major service was due for my MY06 9N3 Polo GTI, which recently ticked over 90,000km.

I ended up changing the Timing Belt, Timing Belt Tensioning Pulley, Water Pump, Accessory Belt and Thermostat as preventative maintenance.

This is the very compact engine bay, where VW managed to cram the 1.8T engine from the outgoing Mark IV Golf (unfortunately detuned) into the facelifted Polo. It is a great feat of engineering tessellation, but it bites when you need to do major servicing.

It was a struggle to find good information on the internet, and I eventually ended up purchasing a workshop manual from erWin. You can buy a 60 minute subscription to all their manuals for 5 euros. Make sure you have all your browsers up to date though - their web interface doesn't seem to like certain versions, and I wasted a good portion of my time switching between computers until one worked!.

I wrote a guide to help others wanting to do the same service:

You will need, as a minimum, the following tools.

• Socket wrenches
• Normal and deep sockets (make sure you have a 5/8" or 16mm one) 
• Ring / Open spanners 
• Torx to square drive bits 
• Hex to square drive bits 
• Allen keys 
• Trolley jack 
• Dead blow hammer
• A lot of patience.

VW Polo 9N3 GTI, 1.8T BJX Engine Timing Belt Replacement Guide

Start by removing the lower engine cover. Removing the plastic shroud in the right wheel arch also helps with access and is highly recommended.
A neat trick that I learnt to avoid having to jack up the car to gain more clearance underneath is to drive it onto thick blocks of hardwood.

Remove the rigid tube that connects to the bottom of the intercooler on the right-hand side. It is held on with two spring clamps.

Here it is removed. 

At the same time, drain as much coolant as possible using the tap at the bottom left of the radiator. You can drain more coolant if you go for a drive first (such that the thermostat is warm and open). This isn't necessary, but it means that more coolant will flood out into your engine bay when you remove the water pump (Ask me how I know!).

Remove the engine cover and coolant reservoir.
I tried to label all the hoses / electrical wires I disconnected with distinctively coloured electrical tape - so I won't forget to reconnect them, and I don't lose any hose clamps).

The upper timing belt cover can be seen in the centre of the photo. It is held on with two clips.

 Remove the upper timing belt cover, exposing the camshaft toothed pulley.

The accessory belt connects the alternator (top middle) and air conditioning compressor (top right) to the crankshaft drive pulley (bottom middle).

Another view, in which you can see the tensioner in the middle.

Remove the accessory belt by releasing the pressure applied the accessory belt tensioner. This is done by turning the "tab" on top clockwise using a 15mm spanner. Remove the tensioner as well. It is held with three bolts. The air intake pipe that connects to the throttle body (shown in the bottom right of the image below), can be removed on one side to give more clearance.

 At this point, I turned the crank bolt clockwise to line up the timing mark on the upper toothed pulley.

I marked the belt surface and the timing pulleys, so I could have additional reference points during reassembly. Put two marks on the upper timing pulley.

Remove the accessory belt drive pulley (which also acts as a harmonic balancer). A 12 point socket is used to prevent the crank from turning when the 4 Socket-head Cap Screws (SHCS) are removed. I put marks on the crank bolt, pulley, and the cover behind it, so I could have additional "check-points" during reassembly.

The lower timing pulley now be seen.  Put only one on the lower timing pulley (so you won't mix up the marks when reassembling).  

The next step involves removing the engine mounts. The timing belt loops around one of the mounting points, so it is not possible to replace it without doing this. This requires one side of the engine to be supported, ideally in such a way that allows you to move it up / down slightly as required to remove the engine bracket bolts.

I also wanted to remove the tensioner pulley (so I could replace it), and the hydraulic tensioner cylinder (so I could compress it). Both these things require the removal of the engine mount and bracket.


The workshop manual calls for an engine lifter bar. I didn't have one, and did not want to make one either. I had an engine crane that I could've used, but that takes up a lot of room (which I didn't have in my driveway), and requires effort to set up.

Instead, I used something a bit more creative. On the engine block casting at the back of the sump, there is an unused ~14mm hole (most likely used for fixturing during manufacture). I put a short M12 stud through this hole (shown in the photo below) and tightened it with nuts. This now gives me a jacking point that I can use with a hydraulic trolley jack to maneuver the engine from below. Note: this is my own technique, and is not recommended workshop practice. Use at your own risk.

After propping up the engine, remove the three large bolts in the "wing" that connect the engine mount to the engine bracket.
Also remove the nut that holds it to the rubber portion of the engine mount.
Also remove the rubber engine mount.

I didn't take any photos at this stage, as I was busy wrestling with the engine bracket (the piece that attaches to the engine block itself). You will have to jack the engine up / down, and use various ring spanners / sockets to undo the three bolts that attach the engine bracket to the engine block. Annoyingly, they used 16mm (or 5/8") hex heads, which really limited the range of tools I had to choose from! 

After removing the bracket, remove the lower and middle timing belt guards, which are held with T-30 Torx screws. The timing belt tensioner and pulley, and water pump, will be visible.

To remove the timing belt, loosen the nut holding the tensioner pulley in place. If this does not give enough slack, then find the 8mm hex hole in the timing belt tensioner pulley (see photos further down), and use an hex key or bit to turn it counterclockwise. This acts to compress the hydraulic tensioner and should get you some more clearance.

Remove the tensioning pulley if you intend to replace it (mine was actually in perfect condition after 90,000km). Do not lose the washer that is under the nut which holds the tensioner pulley.

Remove the water pump if you intend to replace it. Prepare for a flood of coolant.
Apparently on some models, VW used a water pump with a plastic impeller, which would become brittle and break, releasing pieces into the coolant system and reducing the pumping efficiency. I was pleasantly surprised that my car (MY06 model), had a metal impeller, which was in fantastic condition. (I was also slightly disappointed, as I had purchased a new water pump!).
It's worthwhile replacing it for preventative maintenance, as it is a pain to get access to it.

The workshop manual recommends recompressing the shaft on the hydraulic tensioner using the tensioning pulley itself, and locking it in place with special locking plate. You will have to remove the hydraulic tensioner if you are doing this without the special VW tools, as you will need to make a locking plate (see below).

I didn't have that special plate, so I removed the hydraulic tensioner and made a suitable locking plate with a piece of 50x50x3mm steel angle. I bandsawed it to the correct width, filed the sides to get a nice fit in the tensioner, and made a 5mm slot (using a 5mm drill, the bandsaw, and a file).

The timing belt tensioner is a hydraulic mechaism. My guess is that it is of similar construction to the gas struts used in computer chairs. It seems VW intended that the tensioner provides a constant pressure on the belt that would not be influenced by engine loading, temperature or belt condition.

I compressed the tensioner slowly in a vice, and used the plate to hold it in place once fully compressed. I'm not too sure what happens if you compress it too fast - I suspect you may damage the internals by overpressurisation as oil tries to flow through a small orifice. Note: you can feel that less pressure to compress it when the internal oil is given enough time to flow from one compartment to another.

At the same time, you will also need to make a special tool for the turning the cam on the tensioner pulley, which has two 3.3mm holes for a pin wrench. I made one with a piece of scrap steel, and two 3mm pins (cut from a piece of silver steel rod from a CD drive). The pins are inserted into two 3mm holes, drilled 18mm apart. The burrs on the hacksaw-cut pins and made for a gentle interference fit.

Side trip : Thermostat replacement

Now is a good time to replace the thermostat, since the accessory drive belt is disconnected, and there is more room to wrestle with the alternator. And it is exactly that - a wrestle. Replacing the thermostat is not necessary, but I was seeing some slight coolant temperature fluctuations when driving, and decided to replace it just in case.

The thermostat housing (shown in the centre of the photo below) is located behind the alternator. Unless you have very small hands, you will probably need to remove the alternator.

Start by removing the two long bolts that are next to the front face. There is also another bolt on the side, connecting to the intake manifold. After that, remove the alternator from the mounting points using a combination of deadblow hammers with pieces of wood, and pry bars.

Prepare for a flood of coolant and remove the two bolts holding the thermostat housing. Replace the thermostat and the O-Ring. Reinstall in reverse order.

For the alternator, I suggest putting a lot of grease on the mounting points. Use a deadblow hammer with wooden blocks to "massage" the upper bolt hole into the right position. If you can manage to insert the upper bolt, then you can use that as a pivot point and whack the top of the alternator to swing the bottom bolt hole into the correct place. Retighten all three bolts.

Back to the timing belt:

Reinstall the water pump. It is good practice to moisten the O-Ring with coolant first so it goes in easier. I found that twisting it in is more effective than pushing.

Transfer the marks from the old belt onto the new belt. These act as secondary references. Put the timing belt over the upper timing pulley, the tensioner pulley, the lower timing pulley, and the water pump, in that order (as it makes it easier). Match it up with the marks you made on the timing pulleys.

Temporarily reinstall (with one bolt) the lower timing belt cover and the harmonic balancer to see if the second timing mark matches (highlighted in white below). If you've set the upper timing belt pulley correctly, these marks should match (unless you jumped a tooth with the original belt due to jerky gear shifting, or someone botched an install with the belt you just removed). You may have to shift the crank position and harmonic balancer positions slightly to get a perfect match.

Lightly tighten the timing belt tensioning pulley with the nut and washer. Leave the socket wrench in place, as you will have to tighten it up after adjusting the position of the cam. 

Using the pin wrench, turn the cam on the tensioning pulley counterclockwise. This will apply force to the hydraulic cylinder and release the pressure on the locking plate. 

Remove the locking plate. Allow the pin wrench to relax clockwise as the hydraulic tensioner starts pushes against the plate connected to the cam. You want to set the gap between the cam plate, and the body of the  hydraulic tensioner to be 4 +/- 1mm, as per the workshop manual. The manual recommends doing this with a 4mm drill bit as a gauge, and bring generous with the clearance, as it will be reduced when the pulley is tightened. 

Tighten the pulley when you think the cam is correctly positioned. Correct torque is 20Nm + 45 degrees. 

Turn the crank over twice clockwise (which is the direction of rotation of the engine) and check that the timing marks match up. Also recheck tensioner clearance that you set above. Adjust as per above if it is not within 4 +/- 1mm. 

Congratulations: you have passed the halfway point

Reinstall the lower and middle timing belt guards with threadlock on the bolts. Correct torque is 10 Nm (although good luck getting a torque wrench in there). 

Reinstall the harmonic balancer with the 4 SHCS.  Ensure that it is lined up correctly as there is a small pin on the timing pulley. Correct torque is 25 Nm.

Reinstall the engine bracket. Make sure the bolts are already in the bracket before inserting it. Correct torque is 45 Nm.

Install the engine mount "wing" and tighten the three bolts. I used threadlock on these bolts, but it may not be necessary (as the manual does not specify it).

Gently lower the engine onto the stud of the rubber engine mount. You will have to adjust its position as it is lowered.  Reinstall the nut on the engine mount.

Reinstall the upper timing belt guard.

Reinstall the accessory belt tensioner. Correct torque is 25 Nm.
Put the accessory belt over the crank pulley, compressor pulley and alternator, in that order (as it is easier).
Pull back the tensioner pulley using the 15mm box spanner (as outlined above) and put the belt over it to tension it. Ensure that all V-shaped ridges are in their corresponding grooves on the pulleys.

Reinstall the coolant expansion tank.

Reinstall the lower air hose and and all the guards.

Reinstall the upper air hose (where the throttle body is).

Reinstall the engine cover.

Reinstall the wheel arch shroud and the lower engine cover.

Refill the coolant tank with VW G12++ Coolant (the purple stuff). (The green coolant is incompatible.) The minimum mix ratio is 40% coolant to 60% water (use distilled or deionised water). Higher mix ratios are recommended for colder climates.

Double check that everything is connected and that nothing is under the car.

You are now at the moment of truth: 

Cross your fingers, start the car and go for a drive (if all goes well).

Drive for at least 10 minutes to ensure that the thermostat opens. The coolant level will drop and you will need to top it up (a warning will most likely sound after a while).
Note: the cooling system is under pressure - so opening the cap on the coolant expansion tank will cause coolant to be forced upwards and steam to escape. Either wait until the car cools (the proper method), or do this very very slowly (the less proper method).

If you've made it this far you're done - Congratulations on changing a timing belt. 

It took me two afternoons, and saved me at least a thousand Simoleons.

Disclaimer:
It's embarrassing (and expensive) to explain to a mechanic that you need an upper engine rebuild because you've bent your valves, a new sump because your engine hit the ground, or both!

If this anything in this tutorial has you confused and/or intimidated, go to a mechanic.
If you are not confident in your mechanical abilities, go to a mechanic.
If you definitely need to finish the job by a set time, go to a mechanic.
I take no responsibility for what you may do to your car by following this guide. Just because it worked for me, it may not work for you.