I have a TM 86 magna that has had a slight timing chain rattle since I got it. only when warm for some reason! I've had it since about 96 and apparently the chain had just been replaced. My question is, How do you know when to replace something without being able to acctually see the guides ect? As far as I can attain, they don't normall fail until the guides wear down to metal, that chewing the chains down unitl they break, thus you would expect that you change them when the rattle changes in sound suggesting that the guides are shot, and you change it then.

Surely most of the time people would just have them break, but wouldn't that mean that every magna would end up with a engine thats not worth replacing, as the valves would go through the pistons, or is this not ALWAYS what happens, and the engine just won't run? Do the valves always go through the pistions when the chains fail, or just sometimes?

**EDIT**
Damn wrong forum!

Rattle when a first start up is no real concern

Rattle at idle is getting to the point that you need to replace it

The myth is that the timing chain is the culprit, it is actually the balance chain that causes most of the trouble, with exception to the start up rattle which is the tensioner for the timing chain filling up with oil. The valve on these gets weak and will not hold pressure, another good reason for frequent oil changes with good quality oil.