Genuine 1995 Audi 90 Piston

1995 Audi 90 Piston Parts and Q&A

• Q: What checks should be performed on the pistons and bores for signs of damage and wear on 1995 Audi 90?

  A: Check the pistons and bores to notice any glaring evidence of damage and excessive wear; and, finding them satisfactory, proceed with the next checks. The piston diameter should be measured at the position 10 mm (0.4 in) below the lower edge of the skirt, at right angles with the gudgeon pin axis, making sure that there is not more than 0.04 mm (0.0016 in) wear maximum. Install a piston ring into the cylinder bore and press the ring down with a piston so it is square and approximately 15 mm (0.6 in) from the bottom and then measure the ring endgap with a feeler gauge, in case the gap is larger than the top limit, check bore wear or measure the gap with a new piston ring. To measure the direct bore diameter, a dial gauge with an internal measuring attachment must be used and measure each bore on 6 point, compared to the wear limit, 10mm (0.4 in) above the top, 10mm (0.4 in) below the bottom, and at the centre, parallel and at right angles to the crankshaft. In the event that a bore is too wide, all four should be rebore and a new set of pistons must be installed to ensure that the engine remains in balance and connecting rods should be installed as complete sets. Check the clearance of each piston ring against the sides of its groove; large clearances are probably due to groove wear and not ring wear, and a new piston would be required. In case of the installation of new piston rings, then remove the wear ridge on the top of the cylinder bore or apply a stepped top ring.