Car when leather belt, how does ability know to should be changed?

when leather belt serves as engine distributing gas when the transmission belt of system distributing gas, everybody knows its value, if when leather belt appears rupture, drop tine to will affect engine valve work directly, and the consequence that still can cause a piston to carry spiracle on the head, like if engine carried spiracle on the head to also be equivalent to,heavying repair, upkeep costs is very tall. We are at ordinary times cannot be judged from the exterior when leather belt needs to change, because a lot of when leather belt ruptures or drop tine to disassemble later, we also have what problem without discovery from the exterior, use year is only too much when the sign that leather belt just has flaw, so pure will look from the exterior is inaccurate. We are changing when interval must change to do according to what manufacturer asks when leather belt, we can change than what manufacturer asks interval changed ahead of schedule a little, can prevent so a certain when leather belt has quality problem to damage ahead of schedule, accomplish no risk at all. So when how long does leather belt change after all? Because this different brand is used when the reason that leather belt sort differs and the locomotive condition of engine differs, change interval has certain difference, model of very much old money uses before us when leather belt is requirement 4-5 year or 8-10 10 thousand kilometers change, but what as the progress on the technology a lot of models are used is macrobian life leather belt, some models ask 10 years or 150 thousand kilometer changes, return some requirements to be able to use 180 thousand kilometer at most, change so interval did not unite a standard. Ask to undertake maintaining changing according to manufacturer to ensure we had better return safety is, actually when leather belt use time is not short also, the price also is not very high, do not have so necessary select penny take a risk to save this, lest cause engine,attaint thed loss outweights the gain.