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Cambelt on SDI. What a horrid job!


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I just read 221. Really interesting, and very similar to the smart car gear system. Thanks for the heads up lupogtiboy. I am surprised that they opted for potentiometers and microswitches (both prone to failure), and didn't use hall senders for everything (much more reliable). The system runs at about 800psi with- and, this is my favourite bit- an electric pump. Brilliant! I'd very much like to know how the pressure accumulator works. On the fsi system they used little metal frizbees stacked together that could flex to sustain fuel pressure. I wonder if it's the same system. Does anyone know of anyone on this forum who's worked on a vw electronic manual unit?

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You don't 'need' locking tools, but they are handy. The difficult bit is not making sure the timing relationship is correct (you can simply count belt teeth if you must...), but undoing and tightening the hex bolts that hold the pulleys on. That's when I usually reach for a locking tool.

You cannot use the teeth for this for a very obvious reason. To tension the belt, you need to loosen the two bolts that secure the cam wheel to the camshaft and then tension the belt, with the crank and camshaft locked. You then re-tighten the two bolts. Therefore the relationship between the camshaft position and the position of the teeth on the wheel would have changed. If you don't do this operation you cannot tension the belt correctly.

As an aside, the 3L gearbox is a lightened automated manual gearbox. The clutch is a normal manual clutch controlled by a hydraulic actuator, using a cable. One mode is called Tiptronic simply because the driver doesn't need to operate the clutch! It has no relationship whatsoever to what is commonly known as a DSG. My advice to certain people is don't write about subjects that you know nothing about!

RAB

Edited by RAB
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Wikipedia?

The font of all the wrong knowledge!

It does have a 'tiptronic' mode, but essentially its a automated manual gearbox

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To tension the belt, you need to loosen the two bolts that secure the cam wheel to the camshaft and then tension the belt, with the crank and camshaft locked.

The penny just dropped. Everyone has been talking about two different things. Me included.

On a PDI engine, you do 'need' the cam timing setting tools (which RAB been refering to as locking tools), and on regular SDI and petrol engines you need the crank locking tool (which I've been refering to). There is no facility on the majority of VW engines to adjust the belt to camshaft timing relationship since the cam belt pulley is locked to the camshaft with a woodruff, feather or peg (or whatever you like to call it). On a PDI engine it is critical to set the camshaft to crank timing relationship since the camshaft is what is used to set the ignition (injection) point. Get that slightly wrong and the engine would run incorrectly (timing out by perhaps only a couple of degrees). Knocking or late injection....

When you set the ignition timing on a PDI, VW specify the temperature it should be set at (I can't remember what it should be), to allow for block expansion, which changes the timing. I had a 1.9 that I worked on a while ago and we were perplexed why it wasn't running 'just' right, even though the person who'd changed the cam belt did everything by the book. Except that he did the belt change outside in freezing temperatures. When the engine heated up to normal running, the injection point was about 4 degrees advanced. It knocked and pinged like an impact driver! (The belt shrinks very slightly when heated= shorter belt. Block expands slightly increasing the distance between belt pulleys = bigger gap so cam pulley has to rotate to get back where it should be= combined error of about 3.5 degrees!!!!).

So everyone is right! (this thread is about the SDI) :) Sorted.

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The official VW instructions for changing a PD belt (Elsawin) don't contain any reference to temperature whatsoever. On a SDI you need to lock the pump, not the camshaft. That is because on a PD the camshaft determines the injection point whereas on an SDI, the pump determines the injection point. I've not seen any reference above to a pump locking tool.

Instructions here:http://www.ccw-tools.com/uploads/images_products/PDF/Instructions/VS4740.PDF

RAB

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I don't bother locking the pump... Just use the paint mark (quicker). Never failed me yet.

I guess what this thread does show is how everyone has their favourite method to work on a car. There is the manufacturer recomended method, and then there is the creative way.... I like the creative method, but then automotive engineering design is my job and I don't like following rules :)

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Snap, I've been in the trade quite a few years now and you find your own way of doing things, sometimes you need to do things by the book, sometimes you just need a bottle of tippex and a buzz gun.

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Well if you know what you are doing then I'd expect you not to pay a garage to do the job anyway, surely that's the biggest false economy ever, getting someone else to do a job you're capable of doing yourself.

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