AEB Engine - Interference Fit?

[stu_rat]

Is the AEB engine an interference fit?

[Crasher]

The 1.8 20v almost always hits and the middle inlet valves get badly bent and damage the pistons. After rebuilding it is not unknown to suffer con rod failure, the powder metal sintered rods don’t take kindly to the shock.

[stu_rat]

Thanks.

The reason I ask is that I changed the timing belt today. I lined up the marks on the camshaft sprocket and cam cover, and on the crank pulley and lower timing cover before the strip down. I also removed the plug from no.1 cylinder and put a long screwdriver in to make sure it was at TDC. After removing the crank pulley, I put a dab of white marker on the end of the crank nose, so I could see if anything moved.

I had to remove the arm that's attached to the tensioner pulley in order to create enough slack to get the new belt on, and I then used an allen key in the slot in the pulley to rotate the pulley clockwise to provide clearance to get the arm in place above the damper. When I did this, the white dot on the top of the crank nose moved clockwise slightly, but there was no corresponding movement of the cam sprocket. Before going any further, I put the lower timing cover and crank pulley back in place, but found that there was some play in the location stud on the crank sprocket, enough to make me lose confidence in the accuracy of the no. 1 crank throw being exactly at TDC. Nevertheless, I turned the crank through two revolutions and the cam sprocket marker came back to where it should have been, but the white mark I'd put on the crank nose was out by approximately one tooth in a clockwise direction.

I backtracked and removed and refitted the belt, but this time I turned the crank a fraction anti-clockwise beforehand (i.e. a rotation of one tooth on the belt) so that when the tensioner took up the slack and caused a small rotation of the crank, the white dot was where I expected it to be. Everything lines up when I turn the crank through two revolutions.

If I've got this wrong, then the belt is out by one tooth at the crank, which I think means it is effectively out by half the pitch of a tooth at the cam sprocket. Will this amount of difference cause a catastrophic failure?

[FrenchAudi]

You should check that the crankshaft and camshaft timing marks line up correctly with the lower cover and the vibration damper in place.

The Haynes Manual has clear instructions for loosening and slacking off the tensioner wheel, and for adjusting the tensioner after replacing the timing belt.

This procedure should be followed to make sure the new belt is properly tensioned.