Timing belt / destroying engine on A8 - S8 .... ?
01-22-2003, 09:12 PM
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Timing belt / destroying engine on A8 - S8 .... ?
Hey guys,
friend of mine has 98 A8 w/70K miles, mechanic told him that especialy on Audi, if timing belt breaks or slips teeth could make serious damage to the engine - valves. Then he said he is not sure about V8 engines, but 4 & V6 happens a lot.
I dont' have to worry yet, but how come does is happens to Audi more than probably to other cars,
or Audi - V8 engines are exeption ?
Any ideas ?
Mark
01 S8 silver / black
20K miles
friend of mine has 98 A8 w/70K miles, mechanic told him that especialy on Audi, if timing belt breaks or slips teeth could make serious damage to the engine - valves. Then he said he is not sure about V8 engines, but 4 & V6 happens a lot.
I dont' have to worry yet, but how come does is happens to Audi more than probably to other cars,
or Audi - V8 engines are exeption ?
Any ideas ?
Mark
01 S8 silver / black
20K miles
01-23-2003, 03:44 AM
#2
Re: Timing belt / destroying engine on A8 - S8 .... ?
Audi has a timing belt, and an interference engine. "Interference engine" means the valves and the pistons inhabit the same space, but at different times. Many (most?) modern engines are of this design, especially any reasonably high performance engines. If the timing belt breaks/slips, "interference" likely occurs, which is catastrophic.
I don't think this happens to Audis more than other cars.
Any ideas? Change the timing belt somewhere in the 75k-90k range.
I don't think this happens to Audis more than other cars.
Any ideas? Change the timing belt somewhere in the 75k-90k range.
01-23-2003, 04:29 AM
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Re: Timing belt / destroying engine on A8 - S8 .... ?
I think the "issue" may relate to the 1.8T belt. The 90k-120k interval (depending on where you read) is about 2x too long based on a number of reported belt failures in the 75k range. Most owners of 1.8T engines that are concerned about engine life now replace the timing belt around 50k-60k.
I am sure there are 1.8T belts that have run well in excess of 120k before being replaced but with the early failure reports, even if they are only one in 10000, the recommended interval isnt good enough for me. I will do the one on my A4 at 50k. Cheap compared to the alternative of a new engine.
I am sure there are 1.8T belts that have run well in excess of 120k before being replaced but with the early failure reports, even if they are only one in 10000, the recommended interval isnt good enough for me. I will do the one on my A4 at 50k. Cheap compared to the alternative of a new engine.
01-23-2003, 04:48 AM
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The never ending effort to achieve ...
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more HP, better fuel economy, and lower emissions with a higher compression ratio and variable valve lift inevitably results in an interference engine. It's common for all high performance motors.
1. The A8/S8 has a relatively high 10.8:1 compression ratio. Since the piston top always tends to be flush with the deck of the block at top dead center, raising compression ratio means reducing the size of the combustion chamber, bringing the valves closer to the piston. All's fine unless valve timing is wrong; and then, as Jim said, the valves and pistons try to occupy the same space at the same time.
2. "Low" valve lift tends to give reduced emissions, but low HP at high RPM. High valve lift results in poor emissions and fuel economy at low RPM but good HP at high RPM. Variable valve lift results in the best of both, but again, the high lift valve will occupy the same space as the piston if timing is off.
more HP, better fuel economy, and lower emissions with a higher compression ratio and variable valve lift inevitably results in an interference engine. It's common for all high performance motors.
1. The A8/S8 has a relatively high 10.8:1 compression ratio. Since the piston top always tends to be flush with the deck of the block at top dead center, raising compression ratio means reducing the size of the combustion chamber, bringing the valves closer to the piston. All's fine unless valve timing is wrong; and then, as Jim said, the valves and pistons try to occupy the same space at the same time.
2. "Low" valve lift tends to give reduced emissions, but low HP at high RPM. High valve lift results in poor emissions and fuel economy at low RPM but good HP at high RPM. Variable valve lift results in the best of both, but again, the high lift valve will occupy the same space as the piston if timing is off.
