I'm finally getting around to putting the Chevy II back together, and the bearing clearances are a little tighter than what I'm used to running, but a lot of you have done this way more than I have, so I thought I'd see what you think. It's a factory 2 bolt 400SBC block, with ARP studs; the crank is a brand new Eagle 4340 crank, and I'm running Clevite H series bearings. I plan to shift around 7500rpm. All five mains are coming in at exactly .002", whereas I normally shoot for between .0025"-.003". I'm finding a lot of information that says that .002" will work just fine, but nobody really mentions the effects of RPM on proper bearing clearances. I also find a ton of info that says to run .003"-.004" (seems awful loose to me)! Here's an interesting article where Callies says that .002"-.0025" is ideal for any RPM range: http://www.chevyhiperformance.com/t...tblock/4380_bearing_clearance_info/index.html Once the motor's broken in, I'll be running full synthetic, in whatever weight I need to give me oil pressure numbers I'm happy with. (I usually run 5w20). I haven't checked the rods yet... So, anyway, what do you think? Is .002" acceptable main clearance for a street/race motor that will see 7500rpm? Thanks in advance! Steve
You'll probably be fine with .002, but I'd like to see a little more room there. As a general rule for racing and high RPM applications you want the clearances a little looser to accomodate rapid expansion of the crank. Making HP makes HEAT.
They make extra clearance bearings (rods and mains) and you can spit sets if need be. Those cranks are known to be finished on the large side and I would like to see a little more as well Call me if you need help, Tony
Chevrolet says .002-.003, minimum preferred, on mains in the Chevrolet Power Manual. A very smart man once told me to be sure to check the rods for enough side clearance in a performance engine. Larry T
.002 is about perfect. Is it "exactly" .002 or like.0021-2? Plastigage, snap gauge and mic, or dial bore gauge for measuring? It makes a difference with a dial bore being the most accurate. Sounds obvious, I know. Sorry...
If it's dead nuts on, .002 is about perfect. More clearance requires more oil pressure and volume and /or thicker (higher viscosity) oil, which means more power required to drive a higher pressure/higher volume oil pump and thicker oil - and also, more potential for spark scatter and distributor timing variations at high rpm. Also, looser clearances means more oil leaking past the bearings and flying around the crankcase, causing more windage. Both of these things - the bigger oil pump and the additional windage cost power, *especially* at high rpm. Mart3406 ================
I used my dial bore gauge and mics (but they're all made in China swap meet specials) which show .002"-.0021", and Plastigage, which shows exactly .002".
Also ck your journals across ,as well as round some of their cranks can be .0002-.0004 tapered and out of round Not the end of the world .....just that you need to know that your .002 is the tightest Also a 400 main being larger than a 350 I would lean towards .0025 on both rods and mains on something that wasnt stock Tony
If the journals are round,(lots arent, especially when you start playing around with the cheaper aftermarket stuff)and its not a circle track endurance motor, its dead on.Watch the side clearance .015-.017 is what you are looking for with steel rods. Less pump, wont suck the pan dry, lower oil level=power.
I deal only with race engines and all of ours are set up with .002 - .0025 as is yours. We spin them 10,000 rpm plus and all works well. Perfect clearance for 5w-30 synthetic (after break in oil). You're right on the money !
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