[email protected] (Dave Williams)
gnttype  22 Aug 1996
- -> > shop.  Most of those guys just do Chevy's which like "loose"
  -> tolerances. > This will eventually lead to a damaged engine sooner
  -> than if it was > built correctly.  Buick's should be tight.  V-6 or
- > I never saw a Cheby that liked loose clearances and never saw
  > anything written that indicated that it was a good idea.
- Building engines to the max side of tolerances was popular in the '60s and 
  '70s, mostly as a result of the more primitive lubricants of the day.  Lots 
  of engine builders still do this, and the engines need 50w or 60w to 
  maintain any kind of oil pressure when hot.  I have a beautiful steel SBC 
  crank that is very professionally finished at .015" undersize...  
  fortunately it will regrind to .020. 
- Callies has some rather interesting charts in their catalog with oil temp 
  vs. bearing clearance.  Their data shows a nice optimum somewhat looser than 
  the usual .0015-.0020 - somewhere around .0020-.0025. That's still tighter 
  than lots of shops like. 
- I like mine tight, and I have my own boring bar and can barter access to a 
  crank grinder so I can ensure proper sizing.  Prior to this all I could do 
  was measure after the parts came back.  Twice I got blocks back that were 
  supposed to have been punched .030, and miked out at .040... 

[email protected] (Dave Williams)
fordnatics  25 Oct 2000
- -> 1:.002
  -> 2:.002
  -> 3:.0015
  -> 4:.0018
  -> 5:.003
- It's common to see the rear main a thousandth or so under the rest of the 
  journals.  I'm not sure if it's a common wear pattern or if they come that 
  way from Ford; I know some local rebuilders take an extra thousandth off the 
  rear main when they turn cranks undersize.  When pressed, they couldn't come 
  up with any reasonable explanation of why. 
- -> The Haynes manual says that .001-.002 is acceptable, am I OK with the
  -> rear main at .003? I am running a standard oiling system on a street
  -> blower motor.
- For a stock overhaul I wouldn't worry about it.  For a blower motor... I'd 
  pop for a set of .001-under mains and use them on the #5 main, which would 
  bring the clearance to .002.  A single shell (block side) on #1 and #2 will 
  close those up to .0015; the blower adds a lot of snout load and you don't 
  really want too much clearance with the blower. 
- It's okay to mix and match standard, .001, and .002 bearings to zero in on 
  the clearances.  The factory manuals for Ford's "Indy" 255, the "Le Mans" 
  427s, and the "Trans Am" BOSS 302s recommend this procedure; in fact, Ford 
  only sold those bearings as singles, not pairs.  I know it *sounds* strange, 
  but it works just fine. 
- You'll have some leftover standards and .001s; put them back in the box and 
  hang on to them, you never know when you might need them. Particularly with 
  a blower motor...