because a belt is quieter and cheaper to maintain
Quote, originally posted by Fantomasz » so why vw replace belt for chain in 2.0T if belt is better?
Because a chain does not require a SPECIFIED replacement interval.
But that in NO way implies that it will never need to be replaced. (Ask people who bought early versions of the VR6 engine about *that*!) A belt needs to be replaced at specified intervals. A chain needs to be replaced when it starts getting noisy. Usually this will be longer than the normal change interval of a belt, but WHEN the chain has to be changed, it is normally a much more expensive job. It doesn't HAVE to be - a chain drive can be engineered to be easy to replace if that is on the "design criteria" - but it normally is.
For example, on a VW VR6 or on the 2.5 litre inline-5 base engine on Rabbit/Jetta, the timing chain is on the back of the engine between the engine proper and the transmission. If (or more correctly, "when") anything goes wrong, the transmission must be removed in order to service the lower timing chain and guides. This is an enormous and expensive job, and often happens after enough mileage that the car won't be worth the expense of repairing, so off to the junkyard it goes.
People nowadays don't want to do scheduled maintenance. Another trouble is that dealers and mechanics can't necessarily be trusted to do the job right (a good many VW diesels have been wrecked because people have wrongly installed the timing belt tensioners, for example, or installed the belt a tooth or two out of position).
Using the timing chain removes the first timing-belt change from the warranty period so the manufacturer doesn't have to be responsible for anything if its dealers bugger up the job. But, for someone who DOES do the maintenance properly, a timing chain (that has not been designed to be easily replaced) may send the car to junk sooner than a belt will. It is an engineering trade-off.
Properly-designed chain drives don't have to be difficult to replace. It's just that cars nowadays are designed to be throwaway, rather than designed to be maintained.
Modified by GoFaster at 4:58 PM 4-12-2009
because VW started making water cooled engines like 35 years ago with timing belts. They don't like to change things much.
People that hafta replace the chains in the VR6s say: Why didn't VW put a timing BELT on this engine....
Quote, originally posted by GoFaster » Properly-designed chain drives don't have to be difficult to replace. It's just that cars nowadays are designed to be throwaway, rather than designed to be maintained.
Timing belts are supposed to be relatively easy to replace. Compared to chains, they are... but the VW TDI engine timing belt replacement requires such a large (i.e. expensive) amount of labor, and requires more careful following of instructions that dealers sometimes get it wrong, that it seems that VW gave up most of the advantage of using a belt versus a chain.
I suspect it is the stretch and gear wear with chains versus belts. On motorcycles I have seen the chains stretch enough to throw the cam timing out significantly. Gassers can put up with more variation here than diesels.
I don't think that lowering maintenance is VW's main concern.
i have an 06 jetta 2.5 and while i am not very mechanically inclined recently when i start the car in the mornings and the engine is cold cold i here a type of humming sound that comes and goes constantly, 1 sec on 1 second off 1 second on 1 second off. kinda like that and once the car reaches operating temperature the sound isnt as noticeable but if you listen you can still here it. also last night the sound seems to have been coming and going alot faster than usual. and then sometimes there is no sound. today i havent paid any attention but its been doing this ever since the weather warmed up which has been a few weeks now but it could have started before and i just didnt notice
just throwing this out there but could this possibly be my chain in any way? the car like i said is a 2006 jetta 2.5 trip with about 70,000km on it. the car is completely stock except for rims and i have been anal with the maintainence since i got it. i got it with about 40,000km on it.
sry for the rant but im just throwing this out there
No, a worn chain doesn't sound anything like that, and the sound is continuous and varies strongly with rpm. Also, at your mileage, you shouldn't have to worry.
What you describe sounds more like a fuel pump, and not necessarily abnormal, either (depending on how loud it is). If it doesn't get any worse, just mention it next time you are at the dealer?
Aung San Suu Kyi
I have timing gears on my GM 6.2 turbo diesel. They will never have a problem unless I run it out of oil. Also, the timing ever changes. They are more expensive and create more rotational inertia, but they will never fail. I would like to design a kit for my 1.6 diesel and lubricate it off of the intermediate shaft oil. Too bad it takes time and money...