Genuine 1985 Audi 4000 Piston

1985 Audi 4000 Piston Parts and Q&A

• Q: What checks should be performed on pistons and bores to assess damage and wear on 1985 Audi 4000?

  A: Examine the pistons and bores for obvious signs of damage and excessive wear; if satisfactory, proceed with the following checks. Measure the piston diameter at a position 15 mm (0.60 in) from the lower edge of the skirt and at 90° to the axis of the piston, comparing this with the specifications. Push a piston ring into the cylinder bore and use a piston to ensure the ring is square and about 15 mm (0.6 in) from the bottom of the cylinder, then measure the ring gap with a feeler gauge. If the gap exceeds the top limit, check for signs of bore wear or measure the gap with a new piston ring fitted. To measure the bore diameter directly, a dial gauge with an internal measuring attachment is needed; measure each bore in six places and compare the readings with the wear limit, ensuring measurements are taken 10 mm (0.4 in) from both the top and bottom, as well as at the midpoint, in-line with the crankshaft and at right angles. If any bores are worn beyond the limit, they will need to be rebored and new pistons fitted. If one bore is oversize, all four must be rebored and a new set of pistons fitted to maintain engine balance, and connecting rods should only be fitted as complete sets. Fit the rings to the pistons and use a feeler gauge to measure the gap between the piston ring and the side of its groove; if the gap exceeds the wear limit, it is likely the piston groove has worn, necessitating either a new piston or an oversized ring. When fitting new piston rings, ensure the wear ridge at the top of the cylinder bore is removed or a stepped top ring is used.