Hi, I have a 1988 Volvo Penta AQ151B marine engine with a cylinder head problem. This engine is basically the same as the Volvo 240 car engine, but it is stoked to 2.5 litre. The cylinder head is a SOHC alluminium unit with a steel insert ring in No.4 exhaust port. Is this common?. All the other exhaust ports are just plain cast ports, but No.4 has been counter-bored round and a quarter inch thick steel ring inserted to make it round (looks kind of like a big valve seat!!). I have checked other Penta engines and they are the same!. Do the car engines have this?. My head is cracked around this ring and I need another head!!.