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Tackle timing belt changes

By autotech-nath on July 5, 2017

You may love them or hate them, but timing belt changes are not getting any easier. We can probably all admit to having got it wrong at least once and being presented with the obligatory blown up latex glove labelled ‘bag of compression’. Here are some hints and tips from INA, the largest belt component supplier in Europe, useful to avoid costly mistakes.


The engine should be at room temperature when setting the belt tension. When the engine gets hotter it expands, so setting the belt tension of a cold belt on a hot engine will mean it is loose when it is cold and not as tight as the vehicle manufacturer’s process specifies when hot. A cold engine is what we call in the trade a datum, a constant that we should all stick to. It sounds easy, but getting the engine at room temperature before you set the belt tension can be tricky, especially if it’s a quick job and the customer has driven 10 miles to get to you. So, make sure you get a tea break or lunchtime in the process or better still, get it on the ramp the night before.
Always change all the pulleys and tensioners. INA tensioner sets and kits are original equipment components and include all the bits you need to change the timing belt. You have to remove most of the Front End Auxiliary Drive (FEAD) components to do the job, plus they have done the same mileage as the timing belt and can do as much damage as the belt if they fail, so why not change them at the same time?
Some garages believe that vehicle manufacturers dream up a complicated process to deter independent garages from doing the work. It is certainly working but they don’t do it for that reason. VMs will start from the position, “I need X tension to make sure the belt doesn’t fall off until the scheduled belt  change,” they will then develop a process that gets them there as quickly and as accurately as possible, repeatedly. Remember, they must do the same as you on a moving production line and are doing it hundreds of times a day. Admittedly, you have a car hiding all the bits you need to get to, but think of it like this, if it will be OK if you miss a few bits out of the process don’t you think the VM would have done it like that?
This time, thinking about if it actually tells you how to replace all the pulleys and tensioner. Rover KV6 is a good example for this – if you follow the OE instructions with a new tensioner, it comes loose and you bend valves. Another good example is the Vauxhall Corsa 1.7 CDTi, where it says retract the tensioner from the belt and lock it and after fitting the new belt just let it go, but if you have the new tensioner in your hand, which way do you turn it? If you have not got enough information call our technical hotline.
For the same reasons in Step 2, VMs will develop an accurate timing process and tools that produce repeatable engine or fuel pump timing in a production environment, to give maximum performance and minimum emissions every single time. If that involves some expensive special tools then that is what is required and a bottle of Tippex just won’t give the same results!
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Timing belts and tensioners that use friction washers to damp out vibrations don’t like oil or water, leaving a leaking oil seal or a leaking water pump is not doing your customer any favours as you are risking total engine failure. A £2 seal and a few minutes work would be doing your customer a favour.
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STEP 6: FIP pulley banana slots
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One of the most common mistakes, usually due to lack of timing pins or tools, is to not lock the cams and loosen the cam pulleys, instead using the ‘universal timing tool’ Tippex to guess the valve timing. Unfortunately, when it comes to tensioning the belt, not having loose pulleys means you will have a loose side of the belt and a tight side of the belt. The tensioner is usually on the slack side so setting the belt tension in this condition will result in an over-tensioned belt.
With the camshafts locked and the pulleys loose you have an even tension all around the belt, which is how the VM intended you to tension the belt. The same can apply to fuel injection pumps – when pinned, the pulleys can be slackened on banana slots allowing some free movement of the belt.
Relates to Step 3, but some tensioners are not marked and weirdly, you turn it one way and the pointer goes in the opposite direction, just to confuse you. Read the instructions carefully and if you are not sure, or it’s not clear, ask.
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Torque wrenches and torque values are vital pieces of kit when it comes to replacing timing and auxiliary belts and their associated tensioners and guide pulleys etc. With belt loads increasing and space reducing, some of these components are expected to perform harder than ever before. Not using a torque wrench can prove fatal to an engine if the bolt breaks.
Always turn the engine over by hand after the process to make sure it turns OK. If possible, it’s also a good idea to leave the belt cover off so you can see whether the belt sits nicely on the pulleys when running before rebuilding it fully.
REPEXPERT Technical Hotline: 01432 264 264 


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