Main Bearings

[2wheeler]

I was just measuring up my block and crank mains and they measure 2.644 - 2.445 I measured my standard size clevite bearings out to .095 each leaving me with .01. A bit tight so I think I might want different bearings? Same thing with the rods?? 2.220 - 2.100 and a standard size .06 clevite bearing leaves me with 0.00!

[Josh454]

What are you using to measure? 

[VileZambonie]

Be a little more specific on what you are measuring. What engine?

Measure your Mains
#1
#2
#3
#4
#5

Rods
#1
#2
#3
#4
#5
#6
#7
#8

[2wheeler]

Sorry... I was vague on the post as I'm trying to get my crank installed and I keep running back and fourth.  It's a 4 bolt 350 that I had bored .030 and decked, I'm going to throw in some flat tops and use 64cc Double Humps.  I ordered up standard clevite bearings to get me started...  I used a mic to measure the crank and block mains.

I cleaned everything this morning and set the crank into place. I plastigauged using red and came out almost bang on .076. If these bearings measure .095 then I'm pretty sure ones that measures .09 would work... .085 might even be better?  Thanks for the reply guys! 

[o2man98]

Sorry... I was vague on the post as I'm trying to get my crank installed and I keep running back and fourth.  It's a 4 bolt 350 that I had bored .030 and decked, I'm going to throw in some flat tops and use 64cc Double Humps.  I ordered up standard clevite bearings to get me started...  I used a mic to measure the crank and block mains.

I cleaned everything this morning and set the crank into place. I plastigauged using red and came out almost bang on .076. If these bearings measure .095 then I'm pretty sure ones that measures .09 would work... .085 might even be better?  Thanks for the reply guys! 

Seriously, with .09" of clearance you will have no oil pressure and a rattle trap of an engine. You want to be somewhere in the .0025" range.

[2wheeler]

o2man, the .095 is the thickness of the standard clevite bearings I'm using.  I guess it helps if I read the right side of the plastigauge... right now I'm sitting at .004.  The crank has been polished so that makes more sense.  Now I'm thinking I should use bigger bearings?  I can see I'm going to have fun when it comes to the connecting rods also...  

[eventhorizon66]

LOL, so that was .095 mm.

[o2man98]

o2man, the .095 is the thickness of the standard clevite bearings I'm using.  I guess it helps if I read the right side of the plastigauge... right now I'm sitting at .004.  The crank has been polished so that makes more sense.  Now I'm thinking I should use bigger bearings?  I can see I'm going to have fun when it comes to the connecting rods also...  

About .001” clearance per inch of shaft diameter is a good rule of thumb for clearance. Increasing that by about .0005” will add a little margin of safety when starting out, especially for rods. Example: .001” X 2.100 = .0021” then add .0005”, so starting out set clearance at .0026” for a 2.100 shaft.

[2wheeler]

Thanks guys!  Yeah, at first I kept using metric AND imperial... doesn't work too well.   I didn't want to spend the time going two hours round trip for bearings .002 thicker. Sooo I used the original crank that came out of the block (not the polished one I had) and the standard size bearings measured up within specs. I got it together with lots of assembly lube and it turns over without heads at about 30 ft/lbs. I just need to pick up my cam but nobody's open tomorrow! 

[malibu795]

for mains #1 is max .0025" 2-5 is max .0035"

#1 main i run .0015-.0020"
2-5 .0020-.0023"

on a fresh build.

if you got the mics... you can mic the cleance.. journal OD form bearing installed ID will get a more accurate numebr then plaisti guage

if they are too tight for you liking... you can get soem scotch bright pads and clean up the strong back of the journal and clean the shoot out of the bearing seat area... i have seen up to .0003" gain there..

[o2man98]

for mains #1 is max .0025" 2-5 is max .0035"

#1 main i run .0015-.0020"
2-5 .0020-.0023"

on a fresh build.

if you got the mics... you can mic the cleance.. journal OD form bearing installed ID will get a more accurate numebr then plaisti guage

if they are too tight for you liking... you can get soem scotch bright pads and clean up the strong back of the journal and clean the shoot out of the bearing seat area... i have seen up to .0003" gain there..

I am sorry but Scotchbright pads should not even be in the same room as an engine being built let alone used in one. The abrasive in the pads will destroy new internals. Do it right, not band-aid.

[malibu795]

then what do you use to clean the back side of the bearing?

the babit side i clean with lint free rags. and i dont mess with at all.

and naturally.. i clean everything again once im done...

this doen by hand not with any powered tool.

[VileZambonie]

Nothing should be put on the backside of the engine bearings and no abrasives should ever touch the bearings. In fact you should never even touch the bearing surfaces with your bare fingers.

Most of your replacement bearing will not be Babbitt bearings anymore btw. They're most likely aluminum

2Wheeler, are you measuring the crankshaft journals or the bearings? If the crank isn't within spec send it to the machine shop and go with an oversize aluminum bearing.

[malibu795]

sorry learned that from some succesfull circle track engine builder....

gues they are wrong..