Originally Posted by stevesxm

im not sure i agree with a lot of this. assuming i understand what you are saying...

you talk about big clearences for thick cold oil but thats crazy... the oil doesn't stay thick or cold for very long and if it DOES then the rest of the motor is taking a real beating. oil... ANY oil needs to be 200 degrees to work as designed... to stay clean and to flow properly for the application and viscosity it was designed for. and once it DOES get hot for any reason, your film strength is gone because of the big clearence and the failures occur...

and you are suggesting that you selectively grind EACH journal differently on the crank to match EACH individual component assembly ? why on earth would you do that ? have the crank ground properly to the correct size within very good tolerence. have the block align honed CORRECTLY so that IT is the right size and STANDARD have the rods done the same way with proper bolts at the correct preload and then, using your dial bore gage as you say, simply set your clearences by using the 0 or + 1 or + .5 bearings or whatever you need to buy for proper bearings... and you are done and the rotating assy is perfect AND all the hard parts are a standard size ... i can not imagine doing it the way you suggest.

as for the piston to wall clearence... this is a discussion we have had here before... i believe ( exluding blower motors etc) that the vast majority of these motors are over cooled... running a carb motor w/out a thermostat at 140 is just wrong and TERRIBLE for the motor. and the piston to wall as well as other clearences are the reason and one significant reason why the service life of marine stuff seems so low compared to other industries... it has NOTHING to do with the mythical " marine" loads... trucks see the same loads over 10 times the hours that any marine motor EVER does... my f 350 towed a 20, 000 lb trailer up and down the mountains with a 460 gas for 150,000 miles... you think your 502 at WOT for 30 mins a month exceeds that ?

no. there is no magic to any of this. any big block correctly machined to nominally correct tolerences and clearences suited for the application and components specified will work JUST fine without any magic or voodoo. more often than not it is EXACTLY the magic and voodoo... the solving of " problems" that you don't really have, that ends up being the root cause of the next failure.

Originally Posted by nocigarette

I Realize That Everybody Has There Point And Good Ones At That, But When I Go Throgh My 540 This Winter And I Send The Crank And Block Out What Should I Tell The Machine Shop About Where I Want My Tolerances At...............

Originally Posted by Reed Jensen

Shoot for .0025 for the rods. .003 for the mains. Some builders like .0035 for the rear main due to crank flex but I set my mains on a 540 at .003 straight across. That is a safe clearance for your engine if you are running a good multi-viscosity oil such as 20-50 or 10-40. These are pretty standard clearances for a big block Chev engine.

Originally Posted by stevesxm

nitriding is a process where the surface is is subjected to a diffused nitrogen process and, as such merely changes the SURFACE properties of the material... no material is added and no dimensions are materially changed altho it is a hi temp process... the point is that it is not a heat treatment in the traditional sense.. where there is material change in dimension and the heat treatment itself extends into the substrate to a measureable depth... with nitriding you start with a perfectly good crank made of perfectly good material that you could run just the way you have it... and make the bearing surfaces a little bit more resistant to scuffing and casual abuse... but if you grind thru it to the next undersize... you still have that same perfectly good crank you started with... it was a very popular system when crank materials wern't very good and you could toughen up the journals and reduce simple wear.

and smittys analysis of the clearences is spot on