Main Bearing Clearance on Aluminum Block

[Warp Speed]

I wouldn't be afraid to run a thou tighter than I would with an iron block. You need to compensate for thermal expansions, but also load driven expansion from the more flexable main web/block. Imo

[John Haskell]

Chrysler offered a paper many years back, on a study they completed through their development on this subject. It covered oil pressure related to oil clearance, to oil temperature, to RPM. All in a cause & effect chart.

They covered thermal changes in oil clearance using steel to aluminum main caps, from iron, to aluminum blocks, to solid to water blocks. The amount of change was remarkable. Aluminum Oval or Road Race had to be Pre-heated, oil & water. If you did not do this, you got 1 main minimum. Try it in a hot tank yourself.

Oil pump clearance, oil pickup diameters, rotor sizing & line sizes. They had it all worked out for their parts.

They also covered oil pans & pretty much showed the world what did what. Some really smart cats over there.

[cjperformance]

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...

Typo ^^ ?

[cjperformance]

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.

Just to add to the dont slather with loctite,, IF you loctite a cam bearing in place always blow thru the oil feed with compressed air to get rid of loctite remnants that could dry and get pushed into the bearing, also particularly if the bearing has a grooved back or groove in the block, the loctite can accumulate, dry and block the oil feed, i have seen this before.

[Mark O'Neal]

Please allow me to correct you.

"redneck" is one work...

Typo ^^ ?

Sure, but the rednecks I know all work pretty hard.

[pamotorman]

GM specs for main clearance on aluminum block. the cam is 2 gear drive so it turns the opposite direction so that is why the cam bearing oil hole is where it is.