ABY/AAN Camshaft pulley key failure

[skibruce]

I have an ABY engine with a damaged camshaft drive pulley. The cast-in key in the pulley has failed and I have some bent valves to sort out. Does anyone have a fix for that pulley or is a replacement the only solution? Does anyone know what the actual failure mechanism may have been? This pulley is the one with the little window for the cam position sensor.

[scotty33]

From your description, the pulley is the same design as a 7A non turbo 20v part. The key is part of the pulley body and being alloy is not designed to transmit torque like a conventional key would be. It is only for positioning the pulley while the bolt is torqued up. The clamping action of the bolt/washer against the front of the cam (has a built in flange for the pulley to seat against) is what should provide the integrity of the cam/pulley interface. I think a threadlocking product should be used on this bolt (you can see why this would be important) so my guess is either insufficiently tight or no threadlock and it shook itself loose?
I guess you could get a keyway cut into the pulley and make a small key to suit the keyways, buy a new pulley, or if you are confident, you could use a retainer/bearing fit type product to 'glue' the pulley to the cam in the correct position, then torque the bolt.

[skibruce]

Thanks for the input. I am aware that the clamping action is what actually transmits the torque. I had torqued to spec. The cast in key is reasonably brittle (not alloy). At the moment I am thinking that the key was cracked when I rebuilt the head and the torquing, etc. when being assembled finished it, resulting in enough misalignment to bend valves. I should have turned the engine over by hand before cranking the starter. This is my usual practice that I frustratingly didn't do this time ... damn confidence when working on a simple engine.

I may try to cut a key way in the pulley but I am more inclined to use the Tommi's Billet pulley from EFI. It is adjustable to compensate for head planing or for fine tuning.

As you appear to have a couple of 20V Coupe Quattros you may find it of interest that this ABY engine is in a 1990 Coupe Quattro along with it's 6spd transmission. It keeps company in my garage with my daughter's 1991 Coupe Quattro that is running a 3B engine.

[scotty33]

Ooh, would be a good excuse to get a vernier jobbie.
My coupes are 20v 2wd not quattro, they are available like that in europe. I toyed with the idea of uprating them but not much point with only 2wd to put down the power. I take my hat off to you guys that manage to build the cars the way you want them. These days I would prefer a tdi in my coupe to be honest!