Timing Belt

[Chris_Blue]

the rocket science comes from the muppet behind the wheel, who has full disregard for the owners manual, warning and advice labels on, in and around the vehicle, and then scratches the nether regions when their rocket science, the one day at school when they should have paid attention in basic high school science, fails them.

Sounds like a few people i know, maybe including me a bit.

Ah, us Plebs eh? Or muppets.....

Called humans.

[cyclone]

Sounds like a few people i know, maybe including me a bit.

Ah, us Plebs eh? Or muppets.....

Called humans.

[Bazra]

The car has a full dealer service and with 46000 on the clock I"d be disappointed if a timing belt failed never mind a chain which should have a far longer lifespan and is not mentioned as a service item ,also it seems a recurring problem with many engine variants from different manufacturers.

[Czar]

The car has a full dealer service and with 46000 on the clock I"d be disappointed if a timing belt failed never mind a chain which should have a far longer lifespan and is not mentioned as a service item ,also it seems a recurring problem with many engine variants from different manufacturers.

You will find that many timing belts require replacement at or before 36,000 mile intervals, so a failure of a timing belt at 46,000 should not be much of a surprise.

As for timing chains, we can look at many variables to this issue, however, there are a few key factors to why timing chains appear more susceptible today, than say 20+ years ago, 20+ years ago, a chain would happily offer 100,000 miles of service regularly in various engine designs, some designs were prone to rattling more than others, quite a lot of timing chains could be manually adjusted with ratchet adjusters, all chains stretch.

The degree to which a chain is subject to stretch has changed significantly over the years, we've gone from heavy linked bushed bearing single to small bush and roller bearing duplex back to small single bush and roller bearing linked chains, the smaller the chain links, the less effective they are at dispersing heat, factor in that the chain is only splash fed by oil, and in the THP engine, and many other GDI, TFSI, direct injection engines, which run 20°c hotter than a regular port injected engine, then the poor old timing chain is given very punishing working conditions.

You have to also factor in, that today's engines require to be as efficient as possible, to achieve that, you need to add lightness, removal of material, and when you remove material, for weight efficiency, you impact on reliability, to reduce reciprocating friction, we need the components to be light, and as I've already mentioned, lightness impacts on longevity and reliability, furthermore, when the timing chain needs oil not only to lubrucate, but to cool too, it is paramount that the oil level is always kept to the maximum mark on the dipstick !!

[DaveB]

to reduce reciprocating friction,

What is "reciprocating friction"?

lightness impacts on longevity and reliability,

Not necessarily. Advances in materials & design tools such as FEA, CAD/CAM, etc., mean that much lighter construction is possible nowadays - it's all about efficient use of the materials involved

furthermore, when the timing chain needs oil not only to lubrucate, but to cool too, it is paramount that the oil level is always kept to the maximum mark on the dipstick !!

As the timing chain is lubricated by oil circulated by the pump sump level will have no real effect on how well it's lubricated; as long as the pickup pipe is submerged in oil the pump will supply oil at the design pressure & volume. Arguably low oil level means a smaller volume of oil to dissipate heat & therefore possibly higher oil temperatures, but that would only be a real problem under more extreme conditions than just about any road car is subjected to.

Building down to a price is a more significant factor in engine performance & life than trying to save weight!

[DaveB]

What is "reciprocating friction"?

I should point out that I understand what you mean by that - the non-engineers among us may not. Basically, it's just friction in the reciprocating bits, i.e. those that go up & down rather than round & round.

(Hope that doesn't sound in any way condescending!)

[Czar]

What is "reciprocating friction"?

Directional force loadings.

Not necessarily. Advances in materials & design tools such as FEA, CAD/CAM, etc., mean that much lighter construction is possible nowadays - it's all about efficient use of the materials involved

I agree ^^^.

As the timing chain is lubricated by oil circulated by the pump sump level will have no real effect on how well it's lubricated; as long as the pickup pipe is submerged in oil the pump will supply oil at the design pressure & volume. Arguably low oil level means a smaller volume of oil to dissipate heat & therefore possibly higher oil temperatures, but that would only be a real problem under more extreme conditions than just about any road car is subjected to.

Building down to a price is a more significant factor in engine performance & life than trying to save weight!

Partly true ^^^ saving weight has a direct relation to performance efficiency, the THP engine was designed to be a very light unit, implementing the lost foam casting process was just one of the many weight saving processes, in order to produce a very highly efficient unit.

I should point out that I understand what you mean by that - the non-engineers among us may not. Basically, it's just friction in the reciprocating bits, i.e. those that go up & down rather than round & round.

(Hope that doesn't sound in any way condescending!)

Not condescending at all, it's good to know you and others understand too.