Clattering noise from engine after doing timing belt service

It could be so many things that it would be near impossible to diagnose without actually hearing it. Here is a site that helps you diagnose the problem by sound of feel. http://www.autozone.com/UseCase,S001/UserAction,viewSimpleDiagInfo/Parameters,info/getInTheZone.htm

Dear audiacher, If you haven't already figured it out, your problem is in the inability of the replacement Stabilus hydraulic tensioner to produce enough force to maintain the correct deflection of the belt. They are all defective, right out of the box. You can put in a new one and check the dimension of the shaft extension and you will find instantly that it is not within spec. That part was also used on the '97 A8, but I spoke to the product manager at Stabilus, and I don't think anyone is going to provide a functional part. If it is any comfort, I have driven mine making the noise you characterize, and at least there has been no failure. If you are really interested, I can give you more info, like the bulletin that gives the shaft extension dimension. Walter@cads.com

audiacher, you describe the problem perfectly i must say. I have same question already posted for my Audi 90. 1990. The audi comes valve and pistod are non interference on timing in service.i dont expect valve bend in case of timing bellt failure, or turning the crankshaft will timing belt removed unlike where we have interference as in the valve and piston share. other wise a non firing cylinder(s) as result is the easy cause. If not, the ignition timing will have to be adjusted in view of the job done. This is because rough idling as describe will happen only as result of fault in the HIGH TENSION CIRCUIT of the ignition. As the car was doing fine before the service, re-time your ignition.

Depending on the design of the engine, the piston and valve paths may "interfere" with one another and incorrect timing in their movements may result in the piston and valves colliding. (Such designs are also called "interference head" or "interference engines", and include virtually all diesel engines. Conversely, non-interfering engines, such as the Mazda B engine, are called "free-wheeling" or "non-interference" engines.) In interference designs, regular service is especially important as incorrect timing may result in the pistons and valves colliding and causing extensive engine damage and therefore costly repairs. The piston will likely bend the valves or if a piece of valve or piston is broken off within the cylinder, the broken piece may cause severe damage within the cylinder, often also affecting the crankshaft. Some manufacturers, such as Nissan, have switched back to timing chains for the majority of their engines because of the breakage problems associated with belts. However, in some newer engines, timing belts are designed to last the effective life of the engine. Other manufacturers, such as Toyota, use a mix: timing chains on their interference engines and timing belts on their non-interference engines. When a timing belt is replaced, care must be taken to ensure that the valve and piston movements are correctly synchronized. The usual failure mode of a timing belt is stripped teeth (which leaves a smooth section of belt where the drive cog will slip) rather than an outright snapping of the belt, which is very uncommon. Correct belt tension is critical - too loose and the belt will whip, too tight and it will whine and put excess strain on the bearings of the cogs. In either case belt life will be drastically shortened. All engines feature an adjustable tensioning roller to allow correct adjustment of belt tension. A timing belt is typically rubber with high-tensile fibers (e.g. fiberglass or Twaron / Kevlar) running the length of the belt.[3] Rubber degrades with higher temperatures and with contact with motor oil. Thus the life expectancy of a timing belt is lowered in hot or leaky engines. Newer or more expensive belts are made of temperature resistant materials such as "highly-saturated nitrile" (HSN). The life of the reinforcing cords is also greatly affected by water and antifreeze. This means that special precautions must be taken for off road applications to allow water to drain away or be sealed from contact with the belt. Older belts have trapezoid shaped teeth. Newer manufacturing techniques allow for curved teeth that are quieter and last longer.

Visit this site to know if your car has interference timing or not. http://autorepair.about.com/.../bl_timing_belt_.htm

Your timing belt should be replaced every 50-70,000 miles. Carmakers have specified the replacement intervals for timing belts. In this In an interference engine, the valves and piston share the same air space. They never touch, unless your timing belt breaks or skips, and this is a catastrophic failure that requires removing the head and replacing bent valves. Non-interference engines do not risk this contact if the timing belt goes. Nonetheless, either can leave you stranded

Walter- I had the same thing happen to my '90 V8 Quattro about 15,000 miles ago. My tech replaced the new tensioner and found that the second one was defective also. The parts distributor tested several and found one within specs. They overnighted it out and the part manufacturer paid for all the labor and replacement parts. The shop that does my work had not run into this before, (and they do only Porsche, Audi, BMW and Jaguar work) so they called some colleagues in New Jersey who told them what to look for.

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