Genuine Volvo S40 Piston Ring

Volvo S40 Piston Ring Parts and Q&A

• Piston Rings
  30731512
  Q: How should the end gaps of piston rings be checked and fitted to ensure proper assembly on Volvo S40?

  A:

  At this stage it is presumed that the pistons have been correctly assembled to their respective connecting rods and that their piston ring-to-groove clearance has been checked. Before fitting the rings to the pistons the end gaps should be checked with the rings fitted in the cylinder bores. Lay out piston assemblies and new ring sets to ensure that the components are kept together during and after end gap checking. Place the cylinder block on the work surface, on its side, so that it is possible to access the top and bottom of the bores. Take the No 1 piston top ring and insert it into the top of the first cylinder pushing it down the bore by using the top of the piston to help make sure the ring stays square with the cylinder walls, it should be near the bottom of the cylinder bore at the lower limit of ring travel. Note that the top and second compression rings are different, the second being recognisable by the step on the lower surface. With feeler blades measure the ring gap and repeat the process at the upper limit of the cylinder bore and compare the results to the specification. If new rings are being fitted, it is unlikely that the end gaps will be too small but if a measurement is found to be undersize, this needs to be corrected to avoid the risk of the end of the rings coming into contact with each other during engine operation, leading to possible engine damage. Ideally it is best to fit new piston rings with the correct end gap, but when it is impossible, the end gaps can be enlarged by carefully filing the ring ends with a fine file. It is also unlikely that the end gap will be too large, if gaps are too large check that the correct rings for the engine and cylinder bore size are being used. Repeat the checking procedure for each ring in the first cylinder and then for the rings in the remaining cylinders making sure that rings, pistons, and cylinders are matched up. Once the ring end gaps have been checked and corrected if necessary the rings can be fitted to the pistons using the same technique as for removal but starting with the bottom scraper ring and working up. Note the markings of the text on one side of the top and bottom rings which should face upwards when fitted, whilst the middle ring, which is bevelled or stepped, should have the bevel or step facing downwards. Don't expand the compression rings too much to prevent breakage, or follow any instructions that came with the new piston ring sets, as different manufacturers may have different instructions. Do not confuse the top and second compression rings, as they have different cross-sections and when all the rings are in position, arrange the gaps in the rings at 120deg from one another except for the 3-part oil scraper ring where the two plain rings should be 90deg from each other.