Main Bearing Clearance on Aluminum Block

[af2]

Just seeing what clearance you guys that have run with a 2.64" main. Limited warm up and going wet sump. Steel main caps. Rodeck block.

[Walter R. Malik]

Just seeing what clearance you guys that have run with a 2.64" main. Limited warm up and going wet sump. Steel main caps. Rodeck block.

I have always used .0012" /.0016" vertical oil clearance on aluminum block, 400 Chevy main bore size and it probably requires careful and controlled warm-up.

[k-star]

Years ago when I was building my first LS aluminum block engine ( Remember those blocks have steel caps not aluminum caps) I was searching the internet for another issue and came across a few discussions on the aluminum block main bearing clearance. The general idea on those threads is that they needed to lose about .0010 clearance cold to make up for expansion. I tried to calculate the coefficient of thermal expansion for the block and the crank, but that got into some calculus formulas that I didn’t understand. So I did an experiment where I measured the Main bores in the block at room temp and then again after I heated them to about 150. (Note: I know that the mains run closer to 230 for temp but could not get the block that hot). I then heated the crank in my jet washer to 180 and measured that. What I came up with both grew about the same amount. The block maybe a few tenths more. So when I built that engine I made the mains about .0005 smaller then what I would usually run them. Kind of a red neck way of doing things, but I never had any issues with that engine.

[Frankshaft]

Years ago when I was building my first LS aluminum block engine ( Remember those blocks have steel caps not aluminum caps) I was searching the internet for another issue and came across a few discussions on the aluminum block main bearing clearance. The general idea on those threads is that they needed to lose about .0010 clearance cold to make up for expansion. I tried to calculate the coefficient of thermal expansion for the block and the crank, but that got into some calculus formulas that I didn’t understand. So I did an experiment where I measured the Main bores in the block at room temp and then again after I heated them to about 150. (Note: I know that the mains run closer to 230 for temp but could not get the block that hot). I then heated the crank in my jet washer to 180 and measured that. What I came up with both grew about the same amount. The block maybe a few tenths more. So when I built that engine I made the mains about .0005 smaller then what I would usually run them. Kind of a red neck way of doing things, but I never had any issues with that engine.

That's actually a good way to do it. How else could you? I have done the same thing. Its amazing how much a rod for example grows on the housing bore from 2 minutes in the jet wash. I personally think the above clearance .0012-.0016 recommended is a disaster waiting to happen. I wouldn't change them really much at all. I usually do what you did above, about .0005 smaller. If I would normally want .003, I would run .0025.

[af2]

Years ago when I was building my first LS aluminum block engine ( Remember those blocks have steel caps not aluminum caps) I was searching the internet for another issue and came across a few discussions on the aluminum block main bearing clearance. The general idea on those threads is that they needed to lose about .0010 clearance cold to make up for expansion. I tried to calculate the coefficient of thermal expansion for the block and the crank, but that got into some calculus formulas that I didn’t understand. So I did an experiment where I measured the Main bores in the block at room temp and then again after I heated them to about 150. (Note: I know that the mains run closer to 230 for temp but could not get the block that hot). I then heated the crank in my jet washer to 180 and measured that. What I came up with both grew about the same amount. The block maybe a few tenths more. So when I built that engine I made the mains about .0005 smaller then what I would usually run them. Kind of a red neck way of doing things, but I never had any issues with that engine.

That's actually a good way to do it. How else could you? I have done the same thing. Its amazing how much a rod for example grows on the housing bore from 2 minutes in the jet wash. I personally think the above clearance .0012-.0016 recommended is a disaster waiting to happen. I wouldn't change them really much at all. I usually do what you did above, about .0005 smaller. If I would normally want .003, I would run .0025.

That is what I am looking at. Thanks They don't grow as much as one would think.

[Newold1]

I agree, I don't think the crankshaft main bores will grow enough under normal block heat levels to require more than an .0005" allowance and I have never tried clearances under .002" on an aluminum block. Over some larger distances and areas of an aluminum block the dimensional growth can sometimes as with decks can grow by .002"-.003" but even that in my experience in adjusting lifters and valve train I have not seen much greater than that.

[engineguyBill]

Adam,
Main bearing clearance in an aluminum block is not critical, use the same clearances that you would use with a cast iron block. What is important though is the housing bore dimension. Aim for the minimum bore diameter, or very close to it.

[needforspeed66gt]

I setup all the LS aluminum engines with .0017"-.002" max main bearing clearance on a 2.559" journal...many are supercharged racing applications with over 1K HP and on tear down the bearings look like new, great oil pressure with 30 weight, 40 if they're really getting the oil temps up.

[af2]

I setup all the LS aluminum engines with .0017"-.002" max main bearing clearance on a 2.559" journal...many are supercharged racing applications with over 1K HP and on tear down the bearings look like new, great oil pressure with 30 weight, 40 if they're really getting the oil temps up.

What I was thinking Frank and Nate!

[af2]

Adam,
Main bearing clearance in an aluminum block is not critical, use the same clearances that you would use with a cast iron block. What is important though is the housing bore dimension. Aim for the minimum bore diameter, or very close to it.

That too thanks Bill!

[blykins]

I set all-aluminum FE's up with .002" main bearing clearance. No issues there.

Also remember that the blocks grow considerably, which will affect your compression ratio, valve lash, etc. Also remember that you need to do something about the cam bearings....pin them, green Loctite them, etc.

[Dave Koehler]

My Rodeck has aluminum caps, no water. Mains set at .002 average, perhaps a touch less on a couple.
Alum Rods are relatively "tight" also at .0025.
Prime oil, Warm up oil, let the heat saturate the engine, bang on it.
FWIW .003 would be ok also, just results in less oil pressure.
I have run it with both NA with nitrous and a mild blown setup.

[Dave Koehler]

I set all-aluminum FE's up with .002" main bearing clearance. No issues there.

Also remember that the blocks grow considerably, which will affect your compression ratio, valve lash, etc. Also remember that you need to do something about the cam bearings....pin them, green Loctite them, etc.

Is that cam bearing loctite deal a FE peculiarity due to the narrow bearings and limited contact area or something you like to do on all engines?
How to you deal with the loctite if you need to freshen the cam bearings?

[blykins]

I set all-aluminum FE's up with .002" main bearing clearance. No issues there.

Also remember that the blocks grow considerably, which will affect your compression ratio, valve lash, etc. Also remember that you need to do something about the cam bearings....pin them, green Loctite them, etc.

Is that cam bearing loctite deal a FE peculiarity due to the narrow bearings and limited contact area or something you like to do on all engines?
How to you deal with the loctite if you need to freshen the cam bearings?

Dave, I don't particularly like aluminum blocks and don't do many of them anymore, but I secure the cam bearings in all aluminum blocks.

Aftermarket FE blocks use wider cam bearings and generally I only use a narrow one on the front journal to keep from having to carve up a wide one for the distributor gear to clear.

With that being said, I've never had a cam bearing spin, but because of the testimonies of a few other FE builders, I started pinning or Loctiting them in. You can still drive them out....I don't slather them up with Loctite.

I had an aluminum LS block (out of a GTO???, I'm not a GM guy) come in for a build and the cam bearings were pinned in it. Don't know if it had been rebuilt before or if they came that way from the factory, but in my mind, it's just added protection. Aluminum blocks squirm.

[Mark O'Neal]

Years ago when I was building my first LS aluminum block engine ( Remember those blocks have steel caps not aluminum caps) I was searching the internet for another issue and came across a few discussions on the aluminum block main bearing clearance. The general idea on those threads is that they needed to lose about .0010 clearance cold to make up for expansion. I tried to calculate the coefficient of thermal expansion for the block and the crank, but that got into some calculus formulas that I didn’t understand. So I did an experiment where I measured the Main bores in the block at room temp and then again after I heated them to about 150. (Note: I know that the mains run closer to 230 for temp but could not get the block that hot). I then heated the crank in my jet washer to 180 and measured that. What I came up with both grew about the same amount. The block maybe a few tenths more. So when I built that engine I made the mains about .0005 smaller then what I would usually run them. Kind of a red neck way of doing things, but I never had any issues with that engine.

Please allow me to correct you.

"redneck" is one work...