working through the back log of stuff on this new to me 1987 426 cat, it has the perkins engine. i have it all the tin off for other stuff so i thought i would gap the valves. it has sat a lot to say the least. the previous owner says he changed the head gasket at around 1200 hours, it is currently at 2000 hours. my book says .012" in and ex. i found them all at over .020". is my book wrong or was the last guy out to lunch?
Your book is correct - 0.012" with engine cold both inlet and exhaust.
thanks for the response nige, had it running today and it seemed to go good with .012 clearance.