bellhoushing

Greg Reimer 7376 · 03-13-2019, 02:23 PM

A machinist I knew, one of those guys who must stay up nights thinking about new ideas and stuff, took a very accurately machined,decked, squared, line honed and ready to go block, and just for something else to do, decided to check and see if the rear mating surface of the block was accurate, in this, he meant 90 degrees perpendicular to the center line of the main saddles. He put a ready to go crank in it, then a flywheel which he properly torqued, and checked for run out,it was perfect, but when he checked the distance from the rear face of the flywheel to the surface of the block, it wasn't 90 degrees from the crankshaft c/l. In other words, the bell housing flange wasn't the least bit flat, or accurately machined.Now,dealing with a cast iron block that came from the furnace and was originally machined at the OEM engine plant long before it ever was a seasoned casting, that makes sense. I remember cars when I worked in dealers in the mid-late '70s once in a while you would get one with a cracked flex plate. If it's absorbing run out every revolution,how long can you expect it to last? You 4 speed racers, and I love seeing them, trying to get an accurate result using offset dowel pins and God knows what else it might take to achieve an accurate result from a hydroformed or stamped part like that scatter shield,could have a whole host of inaccuracies to deal with. In short, has anybody ever had clutch and flywheel issues due to inaccurate machining of the rear face of the block on back? I'll bet we have,and don't know it!!

03-13-2019, 02:23 PM	#8
Greg Reimer 7376 VIP Member Join Date: Nov 2008 Location: Glendora,Calif. Posts: 1,137 Likes: 172 Liked 719 Times in 220 Posts	Re: bellhoushing A machinist I knew, one of those guys who must stay up nights thinking about new ideas and stuff, took a very accurately machined,decked, squared, line honed and ready to go block, and just for something else to do, decided to check and see if the rear mating surface of the block was accurate, in this, he meant 90 degrees perpendicular to the center line of the main saddles. He put a ready to go crank in it, then a flywheel which he properly torqued, and checked for run out,it was perfect, but when he checked the distance from the rear face of the flywheel to the surface of the block, it wasn't 90 degrees from the crankshaft c/l. In other words, the bell housing flange wasn't the least bit flat, or accurately machined.Now,dealing with a cast iron block that came from the furnace and was originally machined at the OEM engine plant long before it ever was a seasoned casting, that makes sense. I remember cars when I worked in dealers in the mid-late '70s once in a while you would get one with a cracked flex plate. If it's absorbing run out every revolution,how long can you expect it to last? You 4 speed racers, and I love seeing them, trying to get an accurate result using offset dowel pins and God knows what else it might take to achieve an accurate result from a hydroformed or stamped part like that scatter shield,could have a whole host of inaccuracies to deal with. In short, has anybody ever had clutch and flywheel issues due to inaccurate machining of the rear face of the block on back? I'll bet we have,and don't know it!!