Tighten .010 main bearing clearances.

[czimpel]

Wondering how to do this. I have a 4.1 block, and just had the crank turned .010 .010. I should have measure my main bores and given the machine shop the size I needed.

I have .002 - .0025 clearance on all of my mains. I would prefer to be closer the the .0011-.0018 that Earl usually talks about. How can I get these clearances with .010 bearings?

Slowly sand down the main cap on a piece of glass like the oil pump cover?

Thanks in advance!

 

[87GN_70GS]

You could have the mains line bored. Ask the machine shop to close up the hole by staying on the tight side of the tolerance for the housings. You should then be able to set any clearance you desire. Will need a slightly shorter chain.

 

[asloan5]

I've never tried but I have read single layer of aluminum foil behind one or both bearing halves. Could send them out and have them coated .. Like calico or one of the others.


Posted from the TurboBuick.Com mobile app

 

[TurboDave]

I've never tried but I have read single layer of aluminum foil behind one or both bearing halves. Could send them out and have them coated .. Like calico or one of the others.


Posted from the TurboBuick.Com mobile app

Sounds like a backyard, redneck mechanic solution to me! Why not just buy a set of -.001 bearings and start mixing and matching until you get the clearance you want. Perfectly viable solution. Many times it only takes one of the bearing halves to bring things into tolerance. This assumes you have a good set of dial bore gauges, and micrometers to check the measurements.

 

[czimpel]

Sounds like a backyard, redneck mechanic solution to me! Why not just buy a set of -.001 bearings and start mixing and matching until you get the clearance you want. Perfectly viable solution. Many times it only takes one of the bearing halves to bring things into tolerance. This assumes you have a good set of dial bore gauges, and micrometers to check the measurements.

Who makes a +/- bearing in a .010 size. I haven't seen one. I would need .011 to get it correct. If it was a standard crank this would be a no brainer.

 

[ek02]

Have it line honed to the smallest dimension in the specs, 2.687. That may help a little. Main clearance of .002-.0025 will work with a good oil pump if you can't get it any tighter. Oil pressure at idle may be a little low, but it should be OK off idle with a modified pump. I am running a 4.1 now with .002 on the mains and pressure is 22 at hot idle with 10-40, jumps to 70 PSI @ 5000 RPM.

 

[m233roller]

I've never tried but I have read single layer of aluminum foil behind one or both bearing halves. Could send them out and have them coated .. Like calico or one of the others.


Posted from the TurboBuick.Com mobile app

Coating will only get you .0002 to .0003 NOT much !! Shimming the bearings ? NO !!

 

[czimpel]

OK. I'll do some more digging. I'm pretty confident that my oil pump will be able to handle it. I'm still going to get them tighter somehow.

 

[Steve V]

By a couple more sets of bearings. I doubt they are all the exact same size, play mix n match. Keep or sell the left overs.

 

[m233roller]

Iv'e always ran .002 on my mains and have great oil pressure, yes I have done all the oiling mods. I don't really care for the .0025 on a street engine but how many are at that? I'd just run the damn thing. Or do as Steve says, try mixing and matching some bearings.

 

[TurboDave]

Who makes a +/- bearing in a .010 size. I haven't seen one. I would need .011 to get it correct. If it was a standard crank this would be a no brainer.

I guess I assumed you already had the clearances down to 2 to 2 and a half thou.

 

[earlbrown]

Torque up the main caps without the bearings in there and take a measurement of the vertical clearance. Hand lap the caps until you get them down to minimum spec (I'm at a sex convention in Atlanta right now and don't have my block book handy).

Once you get them all to size, reinstall the bearings and see what your clearance are. With any luck they won't get bigger. I've seen that happen once on a SBC that kicked my ass.

It's also a good time time make sure the caps are centered while you've got the dial bore gauge out.

 

[asloan5]

This is where I read it from. Ken is very sharp.


Posted from the TurboBuick.Com mobile app

 

[earlbrown]

I measured heavy duty foil once and it was .001" thick. I would imagine you'd have to have some out of spec main bores to get away with losing .002" of clearance.

 

[czimpel]

It's also a good time time make sure the caps are centered while you've got the dial bore gauge out.

Could you explain what "make sure the caps are centered means"?

 

[earlbrown]

Put the dial bore gauge right at the parting line and take two width measurements. If the caps aren't centered over the bore you'll see it. One will read small and one will read big.

 

[Nick Micale]

Everybody has opinions, so here is mine!

On a stock build we normally use .0020" on the main bearings, and up to .0025" on a performance build.

Our engines usually run 25-35 PSI oil pressure at hot idle with non-synthetic oil, and 50-80 psi at RPM.

Over the past 20+ years with over 600+ turbo Buick engine builds, we have yet to see a bearing failure due to too loose main or rod bearing clearance in our builds.

 

[czimpel]

How about the rod bearing clearances?

 

[thadeal4real]

well since everybody's doing their $0.02 without a proper line hone job just sanding the caps typically just pinches the bearings together on the sides not really lowering the clearance where you need it

 

[czimpel]

Too late. I already hand lapped the caps. Everything measured correctly when finished. I guess time will tell.

Thanks for all of the help everyone.