Why a timing belt?

I don't understand the concept of a timing belt, why not gear or chain driven? Is there an advantage to a belt? I'm just curious as to why they decided to put timing belts on tdi's like my 1.9 instead of using a different safer way to move the cam?

Because VW thinks you will get bored and sell the car in five years, or the lease will run out and you'll give it back. Then it will be someone else's problem.

You're not supposed to want to keep the car long enough to care. It's not good for business. Didn't you see the low low financing offer?

Oh, and it was the cheapest way they could make the engine work. Is there a cheaper way to get it past the warranty period? If you can think of one, they'd like to hear from you.

I'm pretty sure it really falls in line with it's what they have always done... if you look at the VW motors for the last 20 years they have always been timing belts.

This has been discussed endlessly here. Short answer is that VW sees a belt as superior, as do many other manufacturers. Less expensive, quieter, provides reliable performance. Chains are neither trouble or maintenance free. And with current change intervals (120-140K) most initial owners won't have to change it. And when it is due the expense isn't that great relative to other maintenance costs, like brakes, shocks, etc.

IndigoBlueWagon said:

This has been discussed endlessly here. Short answer is that VW sees a belt as superior, as do many other manufacturers.

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The silly thing about that is that all they need to do is look at the Cummins 6BT engine to know that that isn't true. Not a single chain or belt, except the serpentine belt, from the crank pulley to the road. It is all gears: timing, trans, and np205 transfer case, not a single belt. Any clear thinking engineer that is worried more about longevity than cost knows that this is a bomb proof setup. There are many million mile examples and mine has 350k with no major engine work. A belt is only superior when one is considering profit and nothing else, IMHO of course...Mark

On an engine like a 4 cyl VW Diesel, a belt is superior in every way. 1.Completely silent. 2.Maintains near perfect cam timing until the day it is replaced. 3.Easy to service.

Ask anyone who works on overhead cam engines with chains. The amount of slop and cam timing error they develop even after 50k miles is significant. Chains aren't bulletproof either; particularly on overhead cam engines. Guides fail and tensioners usually require attention around 150k to 200k miles and it's much more labor to service that stuff because it's buried in the engine.

scdevon said:

On an engine like a 4 cyl VW Diesel, a belt is superior in every way.

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In reliability when compared to all gears? I don't think any setup is more reliable than gear to gear...Mark

all gears is expensive and NOISEY.

Yes the timing belt (as used in TDIs) is VERY reliable, and simple compared to the alternatives. If it is replaced when scheduled (and the rest of the parts with it) - reliability is maintained AND it holds it timing better.

As for longevity - I think 316,000 miles speaks volumes (latest tank) - and I don't even have the longest running one around....

Gears are heavy, noisy, much more expensive to machine, require lubrication and require more space.

That said I do appreciate that my V4 Saab has geared cam and balance shaft. The rotating masses make the engine smoother, but then having flywheels at BOTH ends of the crank would......

Timing chains are noisy. The link components are cheap to stamp, but there are too many moving parts (at least 8 per link) and when any one fails or wears the entire set is useless. Chains stretch as they wear out requiring tensioners that also require lubrication and slack adjustment fo rmore moving parts. Short chains (cam in block push-rod engines) have fewer links to fail or stretch, but overhead cam engines require longer chains and have more stretch. The cost of chain replacement is multiples of belt replacement do to the chain due to the oil lubricated chain and tensioner being 'inside' the engine.

Belts are quieter, lighter, cheaper to produce, have no moving parts, can be snaked to drive the cam AND the injector pump AND the water pump, are 'external' by not requiring lubrication.

And the Touareg 2.5 R5 with gear driven water pump - due to lubrication there is a neat path for oil through the waterpump seal to get into the coolant system. Extra failure point and a nightmare to replace - these pumps are no more durable than our TDI's.

this is what I am talking about...

Bombproof:

...Mark

scooperhsd said:

all gears is expensive and NOISEY.

Yes the timing belt (as used in TDIs) is VERY reliable, and simple compared to the alternatives. If it is replaced when scheduled (and the rest of the parts with it) - reliability is maintained AND it holds it timing better.

As for longevity - I think 316,000 miles speaks volumes (latest tank) - and I don't even have the longest running one around....

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I'll agree with noisy, but it is not expensive when you never have to replace them. My Cummins is a rattle box, very noisy, but it always starts and it always gets me there and is relatively cheap to fix, because I do all the work on it myself. I can understand why belts are used, but I'll never agree that they are in any way more reliable...Mark

Jebus get off it.....sell the damn thing if you hate it that much...

There is always an expert who can't see the vast forest for the pretty trees.

Noise, need for lube, size (length) of engine, weight, cost, Etc. are some of the reasons to choose one or the other means to drive a camshaft.

All of engineering is a compromise, when you obsess on why didn't they do this or that, it usually means you don't fully understand/recognize/consider all the issues the engineers tried to juggle.

It's a personal problem.

Bill

maybe368 said:

The silly thing about that is that all they need to do is look at the Cummins 6BT engine to know that that isn't true. Not a single chain or belt, except the serpentine belt, from the crank pulley to the road. It is all gears: timing, trans, and np205 transfer case, not a single belt. Any clear thinking engineer that is worried more about longevity than cost knows that this is a bomb proof setup. There are many million mile examples and mine has 350k with no major engine work. A belt is only superior when one is considering profit and nothing else, IMHO of course...Mark

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I love my tdi but I see what you are saying, same goes with powerstroke or duramax it's gear driven. How many threads do you see that a cummins, powerstroke or duramax's valves collided with pistons because of a rubber belt failure vs our tdi's.. Anyway I'm doing the first timing belt replacement I have done on my tdi since I have owned it, belt, rollers, tensioner,all seals, gaskets, bolts and waterpump. It just had me thinking, why on earth a belt with all these things that can cause it to fail at anytime and possibly grenade your expensive motor. But all I can do is take care of it do routine work and drive it untill it finally dies, who knows when that will be, might be tomorrow or might be 40 years from now with a million miles on it.

Timing belt failure is relatively rare. Timing belt failure because someone installed it wrong, timed the car wrong, ignored the change interval, or bought inferior parts are somewhat more common. Avoid those situations and it's doubtful you'll ever have a problem.

Only issue we've ever had with timing belts after owning 8+ TDIs, with some approaching 300K, is my son's water pump seized after the car sat for eight months without starting it. Stripped the teeth off the belt. But the engine didn't lose time. New belt kit and the car was on its way. Still running great.

Blackjedi said:

I don't understand the concept of a timing belt, why not gear or chain driven? Is there an advantage to a belt? I'm just curious as to why they decided to put timing belts on tdi's like my 1.9 instead of using a different safer way to move the cam?

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Yes, there are advantages to a timing belt: it's less expensive to manufacture, and therefore less expensive to purchase initially; it's quiet; it's quite reliable if maintained properly. What more could you want?

Gears are ideal but it would be very complex to drive a OHC engine with gears. The other solution is chains but VAG has a bad history with those and I can tell people you should be kissing the engineers that they did not stick the TDIs with their fail-o-chain setup. Of course VAG usually puts the chains on the back of the engine so when they fail, you either have to pull the trans or the engine.

Why an overhead cam on a relatively low rpm engine ?
Pushrods are pretty reliable in low rpm operation.
Of course the "high speed" Diesels are based on higher rpm gas designs so they follow that direction.
Pushrods with roller tappets would be the ticket.
The one required gear would be neither expensive or noisy.
It would be more expensive than using the existing tooling to manufacture.

The extra weight and resistance would kill fuel economy in a small engine. The duramax.....he don't care. He'll spin 20 pound weights around all day long and get 17mpg and it will seem a wonderous thing.

jasonTDI said:

Jebus get off it.....sell the damn thing if you hate it that much...

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Personally I agree with this ^^^ enough said

bajan

Asked:

redbarron55 said:

Why an overhead cam on a relatively low rpm engine ?
Pushrods are pretty reliable in low rpm operation.

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And answered:

...
It would be more expensive than using the existing tooling to manufacture.

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VWAG is already set up to do OHC bloacks and heads, and the TDI engine is run down the same line as the gasser inline 4 engines. Hence, to set up an entirely new line just for pushrod TDI engines? The bean counters, stockholders, board of directors, upper managment, among others would all be lining up to cast rotten tomatoes and cabbages at your head while it is locked in the public stocks.

Cheers,

PH

I believe belt is an issue for those of us who have experienced a tb failure !!

And there seem to be a lot of people who have suffered this costly "experience"

Btw, my other Euro cars have never broken a timing chain (double row)
and I really don't "hear" them, may hear fan/serpentine belt, but while
I have owned around 50 of these motors, they don't have the sweet sound
of a little 1.9L diesel motor !!!

Best part of this forum - helps teach us how to avoid tb catastrophe !!!!

It's not the belt that scares me, its all the things that can go wrong and cause it to break and jam valves through my pistons... Any of the rollers, tensioner, and waterpump could seiz and cause the belt to break, scary thing is even if these parts are brand new they still could fail... Maybe I'm just a nervous wreck Lol I'm having my mechanic install my timing belt kit with all the goodies... I'm going to be there watching and learning. Then all I can do is pray it all holds together untill next time.

scdevon said:

On an engine like a 4 cyl VW Diesel, a belt is superior in every way. 2.Maintains near perfect cam timing until the day it is replaced. .

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Or jumps a cog

bollweevil said:

Best part of this forum - helps teach us how to avoid tb catastrophe !!!!

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I'd like to think that this forum has saved a head or three over the years.

Right, timing chains are definitely simpler and lower maintenance.

The engine in the picture on the left is from an Audi S4 4.2L V8, the one on the right is the 4.2L V8 from an RS-6. When (not if) the chains need to be replaced (sometimes as early as 100K miles, same as a TDI timing belt) you have to pull the motor, as they are on the rear. Conversely, the timing belts are on the front of the motor in the RS6. Evidently they used chains on the S4 because the belt driven motor was too long to fit the engine bay.

Compare the two setups and then tell me that the chain drive is simpler and more reliable. The chain driven version has 4 chains, 4 tensioners and at least 10 guides. The belt version has 1 belt, 1 tensioner and 3 idler rollers. No contest in my book.

Plastic chain guides crack. Tensioners fail. Sprockets and chain links wear. All of these things lead to loss of timing accuracy and eventual catastrophic failure if not addressed in time.

Personally I'm not looking forward to servicing the chains on my '05 S4. At the same time, I'm not at all sweating doing the TB service on my '10 Golf. I'm much happier with a defined change interval than a "fix it when it breaks and hope it didn't take anything more expensive with it" scenario.

Jim

maybe368 said:

Bombproof:

...Mark

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lol... bombproof but not dowel pin proof.

JLMurphy said:

...I'm much happier with a defined change interval than a "fix it when it breaks and hope it didn't take anything more expensive with it" scenario.

Jim

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ditto

The new EA288 engine uses a belt for the oil pump.