Posted by Matt C on April 25, 2003 at 21:04:40 from 68.45.177.241
In Reply to: need opinions on my idle rattle ASAP pls help!! posted by Andrew on April 25, 2003 at 18:14:29:
Ok,
Only having heard the explanation of what was happening from the first post, I am assuming you are right about it being the chain or something related to it. Timing chains THEMSELVES dont oftem give any warning. If they fail completely the engine and cam no longer work in harmony and in the case of one of our engines, the pistons and valves will most likely meet causing very serious damage to the engine.
Now that being said, there are items related to the chain that could fail that could make a ton of racket in the timing chain region but not actually indicate a chain failure. The major item would be the guide rail asesemblys that the chain rides in and on. The chain also has a tensioner piston and spring that keeps constant pressure on the movable exhaust manifold side chain guide. This guide or "rail" keeps all the slack out of the chain regardless of engine speed. Now the fact that the tensioner/guide could be messed up would mean that you are a bee's eyelash away from the big boom itself and you should not attempt to run the car until you investigate it further(pull the valve cover, distributor and upper timing cover). Now its not a huge job to look at either but i do recommend that you have a shop manual avaiable to use to help you locate and understand how all the parts work together to achieve the desired result. Timing chains that have tensioner problems often times will skip a tooth or 2 and run like crap. If the car is sounding as such and running the same that may have happened. Just do yourself a favor. If you have any doubts about it stop running the engine. The next time could be the big one. I also don't recommend trying to replace the chain and or re-time the chain if you dont have some pretty solid mechanical knowledge.
Good luck. If there is any more info you can give let us know. Matty 76 530i