I've been putting a 4-71 together for my hot rod. I've just about got it finished up but am not confident on my clearances and am hoping somebody can confirm if this will live. I'd rather not blow up the first blower I've put together as some of them appear to be tighter than the manual but this thing must have been running in a similar condition for a long time? I did coat the rotors with Ezslide as recommended in other threads here. Inlet rotor to case 'D' 0.013 - .0.14 (Spec in manual is 0.016 min but how can you change this?) Outlet rotor to case 'E' 0.003" - 0.004" (Spec is 0.004") Rotor - Rotor 'CC' 0.004" - 0.006" (Spec is 0.002" - 0.006") Drive bearing plate to rotor 'A 0.010" (spec is 0.007" min) Rear bearing plate to rotor 'B' 0.007" (spec is 0.009" min - do I really need to pull this thing apart and machine the end of the rotor to maintain this spec?) I have 0.004" of gear backlash.
What I use between the rotors is 0.011 for timing, this is the most important clearance. The rear plate clearance to rotor seems a little tight, I usually open it up to .014 or so. If it's too tight it will gall or weld together when the blower heats up. The most important is to make sure the manifold dead flat when you install it.