Product information

For sale in this listing is a set of 8 pistons to suit Rover V8 engines at 3.9L capacity. The pistons here are supplied with the correct rings and gudgeon pins (please use the drop down menu above to tell us if you require standard size or +20 thou oversize pistons). Please also note that 3.9 litre and 4.0 engines have different pistons and they are not interchangeable.

These pistons will give a compression ratio of 9.35:1 assuming all other components are as Rover designed them, however block deck height, head chamber volume, gasket thickness and gasket diameter on the bore all have an effect on compression ratio so all would need to be measured to know the true compression ratio of your engine. However please do not let this deter you from building your own engine as most engines we build with these pistons, our composite head gaskets and re-manufactured heads sit between 9 and 9.5:1 CR.

RPi Advice

• All 3.9 original pistons are non directional, however many aftermarket pistons are so always look for a dot or arrow, which should point toward the front of the engine.
• The conrods on 3.9l engines are all directional. There is a single dimple on each conrod, and the dimples on each big end journal should face each other. This means the dimples on rods 1, 3, 5 & 7 will face the back of the block (towards the gearbox end) whilst the dimples on rods 2, 4, 6 & 8 will face forwards.
• A few hours before you attempt fitting new pistons to your conrods, put the gudgeon pins in the freezer. The cold temperature will shrink the pins slightly, making fitting easier.
• When installing the pistons and gudgeon pins, the small end of the conrod can be heated to assist fitting. As a guide the rods can be heated until they start changing colour slightly, but must NOT be heated to the point of glowing.
• We always fit new piston rings when rebuilding an engine and recommend that you do too.
• When removing conrods, ensure that the big end caps are kept on the same conrod that they were removed from. Mixing up the big end caps will create issues.
• 1st rings are sometimes directional, all 2nd rings are directional. Our advice is to keep the packaging and instructions that the rings are delivered with as this will contain the information you need. Also be on the lookout for a stamped dot or "top" marking, which will need to face upwards (toward the cylinder heads).
• Piston ring gaps should be as follows:
  1st ring 17 to 22 thou
  2nd ring 17 to 22 thou
  Oil ring 14 to 50 thou
• Brand new ARP studs for the conrods are available from our shop here and are not only stronger than standard studs, but cheaper too.