Can anyone tell me what diameter & thread the exhaust pipe mounting bolt holes in the barrels of a l/s blind head flyer should be (that’s for a siamesed exhaust pipe with three hole mounting – left hand bolt + middle stud + right hand bolt) ? I need to helicoil a new thread into some very stripped holes !!
Just in case anyone revisits this thread, I’ve just checked an unused block and the exhaust threads are 5/16″ cycle and not bsf! It’s possible of course, that Scotts chopped and changed just to confuse!
As Dave says, they were 5/16″ X 26tpi Cycle thread in blind-head blocks, and bolts are freely available from various specialist suppliers. Do thoroughly clean out the blind holes as an amazing amount of swarf and crud always seem to be in the holes, and it can prevent the bolts from tightening down properly onto the exhaust pipe flange.