There are many things in and around the timing belts that should be checked when doing a timing belt job, especially if replacements are done infrequently. (Owners who perform timing belt changes on a more frequent basis (perhaps as part of engine rebuilds or other work associated with motorsports) need not necessarily check everything each time, and will of necessity have the experience to judge what to replace and what not to.)
The following is a list of parts that should be checked, repaired and/or replaced during a timing belt replacement. The list is based off of experience with 1G cars. 2G owners can still use this as a guide, but 2Gs may have certain other specific problems not mentioned here.
For more information on why belts are so important on DSMs, read the section Why is it so important to change the timing belt on a [DSM]? in this FAQ.
|Part||Reason for check|
|All 5 belts||Broken accessory belts can hit the timing belt, causing it to jump or break.|
|Timing belt tensioner||Tensioner can wear out or separate, leading to timing belt failure. [Search for 'tensioner']|
|Balance shaft belt tensioner||Same reason as timing belt tensioner.|
|Water pump||Replacing the pump requires removing the timing belts. Do it while the belts are off anyway if there is any chance the water pump might fail, or if it is near the date for scheduled replacement. Read this post to see what can happen if you don't replace it.|
|Oil pump sprocket and nut||The oil pump sprocket nut can come loose, and damage the sprocket. It can also spray oil over the belts, causing them to fail prematurely. Also, loose nuts can chew through the timing belt cover and may eventually hit the timing belt, causing it to break or jump.|
|Seals for the following: oil pump, balance shaft, crankshaft, and the o-ring under the balance shaft plug.||They get old and brittle, and no longer seal well.|
|Timing belt tensioner bearing, timing belt idler pulley bearing, and balance shaft tensioner bearing||The bearings get dried out. They can be repacked, but are inexpensive to replace. You can also replace the pulleys, but there have been some redesigns and new timing belt pulley may not fit quite right.|
|Crankshaft accessory pulley/harmonic balancer||The rubber portion of the pulley can become old and brittle, and can eventually separate, causing the pulley to fall apart.|
Note that after a timing belt job has been performed by an outside source, it is important to check and/or adjust the base engine timing. Not an alignment issue, this involves taking a timing light and double-checking that the base timing has not gotten screwed up.
This is not as straightforward as it may seem, since the ECU generally controls the timing and can 'fool' the mechanic into believing the base timing is ok. It is necessary to ground the timing adjustment connector in the engine bay to disable the ECU control and allow the engine to run at its true base timing. Otherwise, the ECU will do it's best to dynamically adjust the timing to the 'correct' value, even though the base timing is messed up.
Failure to do this check may result in the ECU lacking sufficient range to advance the timing as far as it should go, leading to a loss of power. Some Digesters have (belatedly) checked their base timing only to find that their timing was set all the way back, presumeably when a timing belt recall was done on their car. Once they reset the timing to the correct value, the car 'wakes up' and runs stronger than ever.
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