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Why Would We Need To?
A phenomenon incorrectly called “chain stretch” is the main reason for requiring a new chain fitting. The thickness of the slide rail, the maximum movement of the chain tensioner and an excessive lengthening of the chain eventually causes issues. Once the tensioner has run out of travel, the chain cannot be properly tensioned.
What Happens Then?
You’ll normally hear more noise coming from the chain, usually a ticking noise which will eventually turn into a rattle. If you continue to ignore it, the amount of deflection in the chain will increase and it will start grinding against the side of the timing chain cover. When you get to this point, it’s not long until it chews all the way through the soft aluminium. Then you start losing oil and it won’t be long until the chain jumps off the sprocket.
Thanks to Michael L who sent these photos just as I was writing this page. Great timing.
It’s a misnomer. It doesn’t stretch but it does lengthen. If the chain was truly being stretched, once the chain tensioner ran out of travel, there would be no more pressure on the chain to stretch it. The transfer of energy between the crankshaft and the camshaft isn’t enough to stretch a chain.
The chain does lengthen over its lifespan however. How? It’s all about the wear. A roller chain contains hundreds of moving parts.
Due to incorrect viscosity, low quality oil, irregular servicing, poor quality oil filters, snapped chain oiler, a seized chain tensioner and general wear.
The pins, bushes and rollers wear against each other causing slack in the mechanism. This means that the inner and outer links pull apart by thousands of a millimetre. These combine throughout the entire chain, making it too long for the tensioning system.
Removing The Chain
The slide rail can be pushed back or the chain tensioner removed and then the chain can be unhooked from the crankshaft sprocket. A new chain can be fed in from the top of the cylinder head and placed around the sprocket before everything is rebuilt.
When it comes to buying new parts, when it’s important like the timing chain, don’t buy cheap shit. Buy it from smart. Since you are there, you may as well change the oil pump chain too.