I think i may start this 572 Hemi project over the winter getting into it over the holidays. I have the BM aluminum block with steel caps. What bearing clearances are needed on the main bearings? I will be using Callies steel rods, so i assume .030 on the rod bearings is fine?

I like my engines a little loose, but I think .030 is way too much. Lol I am pretty sure you meant .003 which i would be fine with.


Joe

Yes .003 with an aluminum block is what I have mine set at. Be aware that when an aluminum block warms up you will see a drop in oil pressure at idle, lot more drop than an iron block. As far as I know that is normal and does not hurt anything.

Yes .003" oops, .030 would be a bit much. I currently have my 511 at .0029 and everything seems fine after several seasons of street romping and a dozen trips down the track. Thanks for the correction.

Yeah, the steel cap with the aluminum block had me guessing on clearance. Want to be sure to get that right.

The rods and crank are both steel, aluminum has nothing to do with it.
.003" is too loose for the rods, .0025"

I have .0022-.0025 on my rods and .003 on my mains on my Hemi.

>003+ on the rods and .004+ on the main bearing in iron block with steel rods work well for me, I'm in the middle of assembling a new KB aluminum wedge block that has .0040+ on the mains and around .0027 + on the rods, I would feel a lot better with .003+ clearance on the Scat steel H beam rods. This motor has a set of CNC ported B1 heads with a sheet metal tunnel ram with two Mark Sullens E85 prep Dominator carbs, I'm going to try NOS on it starting with two kits, 150 on the small kit first and then, maybe, another 300 HP on the second kit if it will (the chassis) take it
I've never used any power adders so this will be the first time
My thinking on any HP or and race motors bearing clearances it is way better to have way to much bearing clearances than a TINY bit too little

OK, so .003 on rods is good and .003-.004 on mains?

You betcha, works good, lasts a long time with 0W20WT standard Valvoline on the street making north of 700 HP and on the track with 10W30Wt (making near 800 HP) VR1 racing oil
The new NOS motor will get those clearances and thin (VR10x30WT) oil also, I'm hoping it will make north of 1000 HP on E85 and then add another 150 to maybe 400 HP of NOS

Ok, Thanks cab. I was under the impression that the 2 different expanding metals in the cap and the block would require something out of the norm for bearing clearance.

Thanks guys

I guess I run my bearing clearances tighter than some racers. 10W-30 racing oil
My previous KB aluminum block had almost identical clearances and never an issue.
BMP aluminum block, steel rods, Callies magnum crank.

Do aluminum block engines require additional main and rod oil clearances? If so, can someone explain why?

I've built a lot of (iron block) engines throughout the years and typically shoot for .002-.0025" on my Mains and .0015-.002" on my Rods. Obviously application and rod journal sizes matter here. I'm talking hot street engines, not full race.

On a race engine I wouldn't be afraid to run .003-.0035" on the Mains and .002-.0025" on the Rods, but I don't see a need for more oil clearance than that.

No

Mine has .0035" on the mains and about .0027" on the rods (steel), if I recall correctly. Don't have my folder here where I keep everything written down.
Mine is a KB block FWIW. Been running it that way since 2006.

I suscribe to the .001"/1.00" clearance/diameter theory. Any tighter is an experiment. Like trying lower oil pressure. Will it work? Maybe? But what advantage is it? As far as going larger. I see no trouble with that either. Oil needs to take away heat and provide a hydro dynamic wedge between the parts. As long as the pump has enough volume to keep a steady flow it's good. At worst .001"-.0015" larger will reduce idle oil pressure. Oil pressure reduction will be far more extreme with loose lifter bores, large push rod holes (pushrod oiling), and large oil feed lines(indy head) than from bearing clearance. Years ago I built and engine with .004"/.004" bearing clearnce. It only would reach 45psi hot with a high volume pump with a external adjuster turned all the way in. So I took it apart andinstalled .001" tighter bearings. The result? no change. Turned out the pushrod holes were so large (.090") that the pump couldn't keep up. Reduced the pushrod size to .045 with roll pins. Had to back the screw all the way out. Then cut a coil off the spring.
Doug

I setup my aluminum Indy Maxx with 0.0035" - 0.0038" on the mains with 400 journals. Number 4 main(0.0038") was not happy when I tore it down after about 100 passes and that journal had about 0.0008" runout. The rod bearings looked perfect and the rest of the mains(except the back half of #3) looked very good considering the number of passes and street miles I had on it. I talked to Molnar and they said 0.0038" might have been a bit too much with the expansion of the aluminum block and allowed the crank to whip killing the #4 main. Given Molar's good reputation, I couldn't argue his logic. This time around I went with a Callies crank and had the block line bored for 440 mains. It's clearanced at 0.003" on the mains now.

FWIW I would shoot for .0030" ish for main clearance. Will depend on the final application, mainly street, street/strip, strip/street or just a race car. Rods depends again on material being used. And by all means restrict that oil going up top. I have my stuff down to .029" restrictors and there is still PLENTY of oil up top. And yes you will loose oil pressure when its warm. Just like an iron block will how much is a guess at best as they all seem yo vary and I have used nothing but aluminum blocks pretty much for the last 12 years.