Cost of repair Audi BMW Saab...(crossposting)

That's interesting. Since all of the brands of cars which I have owned have had them, I just assumed ...

Anyway, how 'bout educating me on two things. Just exactly what do timing belts do? (Yes, I am pretty dumb in this area.) And what do the BMWs w/o timing belts have which perform that function?

Thanks, Bob

Timing belts or chains connect the crankshaft to the camshaft(s). As the crankshaft turns, the cams are rotated to open and close the valves.

In the old days they always used chains. Chains tend to be a little noisier - not much, just a little. In an attempt to eliminate the sound, very slight additional vibration, and to cut production costs, many manufacturers started using timing belts. Because it's a high stress application, timing belts typically go 60K miles although some now go 100K miles. Chains last well over 100K miles in most engines.

The failure of a timing belt can range from "you stop and call a tow truck" to "you just destroyed your valves, pistons, and are looking at $3-6K in repair costs". That depends on engine design and is related to a whole bunch of other issues. That is, it's not that engineers can't design engines that fail gracefully when the belt goes, it's that it forces other compromises to use that type of design. Replacement of a timing belt ranges from $250 to $600 with most engines.

Better name is cam belt - as it drives the camshaft. It may well drive other things as well like the waterpump on some designs.

They went back to chains with the twin cam engines. The rubber band to drive the camshaft didn't arrive - globally - until about '70 - before that most used chains, although there were other ways.

Bob,

Timing belts operate the "overhead cams", which are the things that open and close the valves that let fuel and air into each cylinder of the engine (the "intake valves") and let the exhaust out of the cylinders ("exhaust valves"). The valves need to open and close in sync with the operation of the pistons and the rest of what is going on in the engine. In some cars this is done using a belt. Belts are quieter and (usually) less expensive, but less durable than the alternative of using a chain. Some engines with a timing chain can be almost as quiet as those with a belt, but it has to be carefully engineered. Chains can wear too, and when that happens they tend to get very noisy. Belts usually give no notice that they are about to break like a wearing chain does. The problem is when the belt or chain breaks, the engine stops. In some engines, the pistons keep moving for a few seconds - just long enough to crash into the now stopped valves which potentially destroys the engine (this is known as an "interference" engine). Other engines are designed so that there is still enough room so that the valves and pistons don't crash together when this happens (this is a "non-interference" engine).

Some engines based on older designs don't use belts or chains, but they usually only have two valves per cylinder (one intake and one exhaust) instead of the typical four valves per cylinder that modern (and usually more efficient), overhead cam design engines allow. (Some of the preceding is personal opinion.)

Walt Kienzle

I do not think HP is a very good indicator of engine efficiency, do you? And mpg will only work if the two cars the engines are in are the same (of the same weight and coefficient of drag).

-Fred

Timing belts go from the crankshaft to the camshaft(s), turning the cams to open and close the valves at the appropriate times. Some cars use timing belts, and are subject to frequent replacements, expensive probelms if the belts break, and so on. They are quieter, though.

Other cars, such as most (all non-V6) Saab engines and apparently some BMW engines, use a timing chain rather than a belt. It will wear and stretch over a few hundred thousand miles, but catastrophic failures of timing chains are very rare...they usually get very rattly for a very long time before anything goes wrong, giving the driver plenty of time (months) to do something about it.

Earlier, Saab used timing gears in the V4 engines, which were again noisier than a rubber band (oops, "belt") but give more positive and reliable timing.

I don't know which Audi uses, but I personally will avoid any engine with timing belts. Internal engine components, which you can't visually inspect, aren't something I'm willing to put up with.

Dave Hinz

A timing belt drives the camshaft and valves, by taking power from the crankshaft. The other alternative is a chain and sprockets, which all newer US model BMWs have. A few cars like Ferraris have gear driven valvetrains.

The only US model BMW engines with timing belts are the "small six" engines, which are in the 80s 3 Series, and some 5 series cars -- the 325e, 325i, 528e, and early 525i. The rare 524td is also a small six w/ a belt.

Matt O.

It might be, coming from someone who hasn't *been here* as many years as I have. You'll notice not many of our regulars have taken me up on that remark.

Hey, compared to most other cars, I *liked* my Audis! It's just that I didn't happen to *own* most other cars. I *do* happen to have owned and/or driven lots of *very* entertaining cars over the years, so my perspective is quite different from most Audi devotees.

-- C.R. Krieger (Still cranky)

Uh ... yeah; whatever. BTW, I don't have an 'Xi. It's an '88 535is. RWD. LSD. If it's *really* slippery, it's a Jeep Grand Cherokee ... because the Audi won't start!

*Drifting*? WTF are you talking about? Either it's that 'Rice Rocket' trend from Japan (for which a response is beneath my dignity) or the last book you read on performance driving was written a decade before Mario Andretti won a world championship. I don't know if I qualify for your definition of a "really good driver", but I *do* instruct for BMW and Audi club driving schools. You don't 'drift' an M3! If you do, you're taking your life in your hands because the recovery runs a surprisingly high probability of snap rolling the car! I've been directly involved in racing and speed events since about 1988 and my experience says that your argument is diametrically opposed to fact.

A stunning non sequitur. Even if it weren't a hopelessly desperate attempt to change the subject, *who the hell cares*? Driving *any* car is inherently unsafe! My BMW doesn't have *any airbags* - and I

*like it* that way! So why don't you just stay home while those of who know what it is to *enjoy* driving (something *not* from Ingolstadt or Neckarsulm or stuffed with more high explosives than a fireworks display) do so? Here's something for you to chew on: BMW 507.

-- C.R. Krieger Life's too short to drive boring cars.

Bentley in the '20s made a 4 valve OHC engine with the cam driven by eccentric connecting rods - rather like a steam railway engine.

"dizzy" escribió en el mensaje news: snipped-for-privacy@4ax.com...

The Accord engine you're talking about is only efficient past redline, and its torque is ridiculous by comparison. The mileage figures you're talking about are only good when you drive calm. If you "nail" the Honda, you'll get not only way less torque and satisfaction but also worse mileage.

"C.R. Krieger" escribió en el mensaje news: snipped-for-privacy@posting.google.com...

With the weight of so much experience on your back, it's plain to see you've got behind the times in this aspect. The Jeep Grand Cherokee is a thing of the past! Knowledgeable people talk Tuareg, Cayenne, Range Rover, and Discovery, when efficiency is concerned - not that I am one of those :) The Audi will start, but then again, so will your 535 if pulled by a Land Rover Defender!

I will never doubt how good a driver you may be, because I live miles apart from where you are and much as I'd like to meet you, this is quite unlikely. Oh, well, I seem to remember you call this "tailback trailing whatnot", only I've seen people who do it for a very long time and even on the wet! I remember this as something really impressive.

Why change the subject? I used to drive an Alfa 75 Quadrifoglio V6 about and I must admit I've never had so much fun, not either when I tried a 325i. Still, I wouldn't replace my Audi with any BMW that was not an M3 (a pure joy) or a 330xd (one of the best all-rounders). My enjoyment is better fulfilled when I see many aggressive BMW drivers can't catch up on a really winding mountain pass even though they have bigger engines. Yeah, maybe the feeling is not the same as that in the BMW behind me, but guess who's got the biggest smile on their face?

I'll dig out my Autocar if my nephews haven't swiped it, but they recently did an article on the most popular cars in the UK once you remove fleet sales, and I think BMW moved up quite a bit on the list. Where I work, you could put up a sign on the parking garage as a German car dealership and no one would bat an eye: Bimmers, Mercs, and Porsches galore. I'm shopping for a Passat just to stand out. :-) Emanuel

They bought snow tires, which shockingly few people do anymore; they assume all-weather tires are good enough, no matter what, then blame the car when it's the tires not gripping that's the problem. I'm guilty of not buying snow tires in decades, but I'm in downtown Chicago and things are plowed pretty quickly here so I can get away with it. Also my winter beater is the 944 - easy to push out when it gets stuck. Emanuel

Let me jump in here real quick. I happen to be a 4x4 enthusiast and enjoy a great amount of offroading out here in the beautiful West. In our club's annual extravaganza's we always hire a tri-roller to the site and always have SUV's and 4x4's of various models, makes and levels of customization compete. And when we go out on trails we have members of every marquee persuasion.

*****the only out-of-box AWD/4x4 cars, SUV's or trucks that ever beat the tri-roller (three vehicle wheels on rollers and one wheel on solid substrate, all which changes from wheel to wheel as the vehicle tries to ascend over the ramp) are the Jeep Grand Cherokee with Quadra-Drive, not Quadra-Trac, and the BMW "x" models in either 3 series or X5/X3 form*****

Nothing else has ever made it over the ramp......nothing, and we have seen every model and make on the road in the USA. Quattro, on various Audis, all the LR vehicles, Land Cruiser, 4Matic, Suburu, 4-Motion, Cayenne, Toureg...the list goes on. The tri-roller is the perfect test of which system offers torque to the needed point(s) at the four corners of the vehicle.

The first measure of capability is how the vehicle tries to power the tractioned wheel(s), the next is what rubber it is fitted with. Outside of that, and before issues like articulation and approach/departure/breakover angles, throttle tip-in, gear ratios etc., nothing else matters yet. On slippery conditions, particularly uphill conditions, how the power is applied is the most important factor (assuming proper rubber).

I like the Rangies, and they are better than stock Jeeps in certain areas, but they don't do well in this type of condition. Particularly given their rather high weights. And the Cayenne and Toureg are pretty fair awd units, but also pretty much hype in real difficult conditions. Don't even think that Quattro is the equal of any of those mentioned. Car magazines don't have a clue when it comes to real 4WD/AWD functionality.

Your test is a valid test of whatever it's designed to test. Perhaps as a discussion of uphill driving with very slippery or loose surfaces it's valid. As a test of street driving, I can't see that it matters much.

I have always contemplated the Land Rover Defender as the most efficacious off-road beast and I doubt it very much it can't make it up your three-roller, if anything else can. Then again, if you'd elaborate on why Quadra Drive and the X could possibly be better than the rest of those you mention, I might get to be enlightened :) In the meantime, I have much more than a fair amount of reasonable doubt that your test is not biased.

In our country roads here in Europe, it is usually Cherokees that get stuck first on difficult terrain, and I have yet to see the Porsches and Tuaregs perform, but I can tell you that just about any Land Rover - except for the Freelander, beats the whole legion of Cherokees hands down.

JP Roberts

"Jess Englewood" escribió en el mensaje news:oySoc.54$ snipped-for-privacy@news.uswest.net...

CRK can always be trusted to come up with something like that... I have no airbags either and I like it that way too...

So does my daughter who can ride in the front in *my* car but not any other one that we or various other nearby family members have owned in the last 7 years.

-Russ.

Oh, I agree, I was speaking only to the specific statement I jumped in on. There's no doubt in my mind a Toureg or Cayenne drives better on the street than a JGC :^)