Procedure for tensioning the timing belt

Hi I'm trying to set the tension for the timing belt on my 98 AHU.. every time I turn the tensioner (clockwise) the crankshaft moves off of TDC by quite a bit, but the camshaft and injection pump stay put.. I'm wondering what the correct procedure is to tension the timing belt, or really I just want to know how I can keep the crankshaft from moving.. I was thinking I could have a friend hold a flathead wedged into a tooth on the flywheel while I tension? the belt.

I read that you're supposed to unpin the injection pump.. but when I do that it goes off time, and leave the cam sprocket loose, I've tried this and it makes but like I said earlier while the crank goes way off of TDC the injection pump doesnt move an inch

I place the crank slightly off, so when you tension the belt it pulls it up to perfect TDC. These are different (unfortunately) than the later cars in that the injection pump sprocket is one piece, so it cannot be allowed to move across an inner locked shaft. It is the same as the old IDI VAG diesels.

Lots of cars are like this, actually.

So just set the crank off a little, and then probably leave the IP pinned so it doesnt move off time?

That is what I do, yes. If the crank is moving a lot, you either have too much slack on the non-tensioned side of the belt (between the crank and pump) or the cam sprocket is not rotating freely on the cam when you tension.

Ok I will try it out tonight, thanks for the help

oilhammer said:

the cam sprocket is not rotating freely on the cam when you tension.

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Just checking OP that you've broken the cam sprocket free of the camshaft so that it can rotate on its own, with the back of the camshaft locked with the jig?

I keep the tentioners arm off its hole and out a bit, get it all lined up and were its close as it can be, Keep the cam bolt finger tight. once its all in place put the arm on the tentioner back in its place with a flat head screwdriver, now put the crank at TDC and the IP back to where its lined up again, adjust the cam if necessary and tighten the cam bolt. rotate it though 4 turns and check it all again, it should be perfect, if its not and just a hair off, adjust things via the cam sprocket. this is why there is no key on it and just a press fit.

You are removing the pump lock pin when tensioning the belt aren't you? Not clear if you are or not.

This is required and specified in the manual. I know the PDF on this site has you leaving the pump pinned while setting the tension but it is WRONG.

Removing the pin for tensioning also makes sense. Apply a little critical thinking. If the pump is pinned during tensioning and the crank is "fixed" by the TDC mark or a crank lock there is slack between the pump and crank that can't be taken up by the tensioner.

The pump must be allowed to float during tensioning just like the cam sprocket so the tensioner can pull the slack out of the whole system.

Yes, the pump may move off the pinned position and that's the disadvantage of the AHU design. It may move a lot depending on how careful you are with installing the belt. On mine I usually have to set the pump one tooth advanced from the pinned position when installing the belt.

Once the belt is tensioned check the crank and return it to TDC before torquing the cam bolt. Pump prolly won't be too far off unless there was a lot of slack between the pump and crank.

Yes, I removed the pump pin and left the camshaft loose off of the tapered part. So I got the camshaft and crankshaft perfectly in time but the pump is off time.. when I jammed the pin back in the crank was no longer at TDC

That's the way it is on the AHU and it demonstrates the improvement on the ALH where the pump shaft remains fixed and the pump sprocket floats like the cam sprocket during tensioning.

It should be fairly close. If more than a sprocket tooth's worth of rotation off you should probably move the pump sprocket a tooth so the pin is closer.

Think of the IP pin as a way to get the belt on the right tooth of the sprocket...but that's about it, and that's why you can (and should) remove it before tensioning the belt... no longer needed.

You'll be rotating the pump on its axis to dial in the IP timing, once you get everything back together and the engine running.

So if the IP is off by a tooth can I make up for the difference in VAG? I've tried the procedure at least a hundred times now and I can never get it just right and it's getting really frustrating.. cam and crank are perfectly aligned but the injection pump is off a tooth (according to the marks I made anyway)

Old thread, but need to know, kind of quickly, if all of this also applies to the 1Z?

MarsBar said:

Old thread, but need to know, kind of quickly, if all of this also applies to the 1Z?

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Yea. I always have had struggles with it until I learned the trick of using the cam sprocket to get the final adjustment and using a flathead to push the tensioner arm in its place once the belt it on. If you do that, things lign up much better

MarsBar said:

Old thread, but need to know, kind of quickly, if all of this also applies to the 1Z?

Click to expand...

Yes, they are basically the same engine.