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I'm told that the timing belt on my 1.9 TDI should be replaced every 95,000 miles or four years, whichever occurs sooner. It's a very expensive job and since I've done only 32,000 miles, what is the risk of breakage? Any advice appreciated, even if it only confirms I've got to spend lots of money!
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Regardless of the low mileage, belts still deteriorate with age, hence why manufacturers recommend an 'x' miles OR 'x' years change interval (whichever comes sooner).
Risk of breakage - Well how long is a piece of string? You have to consider whether a belt change is cheaper than an engine rebuild or change.
Edited by Dynamic Dave on 06/08/2008 at 13:46
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I'm not going to contradict any advice you may have been given.
Out of interest, see what the belt change interval recommendations are for this car and other VAG vehicles using your engine in other countries. Start with Holland and Norway (both friendly, dealers like to talk) then try the USA (language almost understandable).
I have a 4 year old Skoda (AWX engine) which is not going to get a new belt until next year.
659.
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I had a new cambelt kit plus a new water pump fitted to my 4 year old 1.9TDi Audi (57k miles) last month for £350 inc VAT at an independent in Wrotham, Kent. Main dealers were quoting at around £600 - £700.
I worry a lot and £350 is not bad at all for peace of mind until July 2012.
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I think in your case you did exactly the right thing. PD engines are very hard on cambelts (look at the width of it) and 57k miles is a bit longer than I would care to leave one - for me, 50k miles / 5 years would be the limit.
Likewise, the water pump change was timely - I hope you found one with a metal impeller.
659.
Edited by 659FBE on 06/08/2008 at 19:03
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I had my belt and water pump changed on my 4.5yr old Golf at 120K for £250inc at an independent - that was christmas last year.
It'll be due another one soon - now running at 138K. I'm tending to change every 60K - 1.5 years approx...
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PD engines are very hard on cambelts (look at the width of it)
How much higher is the peak torque necessary to turn diesel engine cams than petrol?
I also have a gut feeling that belts have a harder time with diesels [presumably the valve springs are stronger?] but have never seen any figures quoted - any Mech Engs out there?
P.S. I never change cambelts - just look after them. Quids in so far...the belt on my A6 [10yrs, 98,000 - inspected and squirted with belt dressing last month] looks almost as large as the belt I saw the other day driving the back wheel of a BMW motor bike!
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It's not the valves, it's the extremely high torque required to operate the unit injectors on PD engines. Superficially diesel engines should have softer valve springs since the rev limit is lower.
A bit of belt dressing snake oil is not going to help if the woefully under-engineered plastic tensioner brakes up. In any case on many modern cars by the time you have got the covers off you are only 10 minutes away from changing the belt anyway.
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The engine valve cams (and more significantly the valve springs) are generally much more mild on a diesel than on a petrol engine due to its lower maximum speed which allows a correspondingly lower valve bounce speed.
The killer on the PD is the injector cams. This engine injects fuel at nearly 2000 Bar (about 30,000 PSI) and has cams like brick walls - and roller followers - to generate this. The cams are very wide and the camshaft has shell bearings as used on a crankshaft to take the load.
I haven't done any sums on the PD as the dynamic loading on the belt is difficult to calculate without detailed data on the injectors, but I would estimate that there is about 3 times the stress on the drive compared with a conventional diesel. The belt is correspondingly very wide.
As a measure of the engineering marginality of this arrangement, VAG contrive to make some of the tooth slots on the crank wheel wider to accomodate the instantaneous belt stretch which occurs as the camshft slows down (injector pressurises) whilst the crankshaft speeds up (cylinder fires). It must have taken several sessions in the pub to come up with that idea - unless the guys at Continental thought of it. The PD engine has a steel tensioner wheel and auxiliary roller.
For all that, the "old" PD is about the most efficient diesel going - work within its limitations and service requirements and it's a very effective energy conversion device.
659.
Edited by 659FBE on 07/08/2008 at 16:54
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Thanks Richard and 659....thats v interesting - the more I learn about modern diesels the more I feel like sticking to low revving non-turbo petrol ECDs for my low-mileage cars!
I entirely take the point about grotty pulleys - had to change a metal one once on petrol Passat at around 150,000ish - [beyond my competence to change belt - 10mins or 10hrs!] - when it started whining - belt was OK, sold at 240,000+ still going strong on original [occasionally snake-oiled] belt - just a small squirt every 20,000 or so.....
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