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So I think I can make the 60/30 pulleys work if I make the end crank diameter .375, once I bore the id some. So to attach the lower pulley I could just machine a flat in the crank and have a setscrew in the pulley like in the pic?Also tensioning the belt is a little tricky because it has to go around the water pump passages in the front cover. I'm thinking one idler at the inspection cover in the head and a tensioner closer to the crank?
Quote from: theeoracle on February 12, 2019, 04:48:02 PMSo I think I can make the 60/30 pulleys work if I make the end crank diameter .375, once I bore the id some. So to attach the lower pulley I could just machine a flat in the crank and have a setscrew in the pulley like in the pic?Also tensioning the belt is a little tricky because it has to go around the water pump passages in the front cover. I'm thinking one idler at the inspection cover in the head and a tensioner closer to the crank? The hub dia. of a 30T cog is about .550in. You will be catching about 4 threads of a #6 set screw with a .375 in. overbore. Dual setscrews with a flat seat on the crank "may" be enough. A solution to inadequate hub diameter is to make a collar to press fit / epoxy around the existing hub and re drill for a longer setscrew and more thread area. You can pre- drill the collar to line up with the hub setscrew holes and drill the next thread size up.Your water pump box is an issue working a belt around by idlers. You would need to be dead nuts on the belt tooth count too. What I would think about, looking at your photo, is eliminate the water pump box section under the cam drive cog for an external cam drive set-up with idlers on engine mounted brackets to give you more lead way as well as a sprocket guard bolted to the engine or as part of the valve cover.
I think I might even be able to use a 42/21 pulley if I bore the 21 pulley out to .375. That leaves .047" of wall thickness, I think that will be enough, what do you think?
If you are determined to an authentic recreation, then that decision is made for you! Which Nissan engine are you modeling and how did they drive the cam?
Quote from: theeoracle on February 12, 2019, 06:19:23 PMI think I might even be able to use a 42/21 pulley if I bore the 21 pulley out to .375. That leaves .047" of wall thickness, I think that will be enough, what do you think?If the wall thickness refers to the cog hub on the crankshaft....you are now down to less than two threads.
They look great Let me guess - you have access to a nice CNC mill ... - don't get me wrong, as this still requires creating a good tool path in order to avoid some not very nice mishaps (if you haven't got a clue about those, you don't know CNC yet ).