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1969 Camaro SS350
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Discussion Starter · #1 ·
Assembling new motor. After checking main bearing clearance torqued caps down to spec. Rotating crank there seems to be slight drag in certain spot during rotation. Pulled caps and #2 and #4 main bearing showed these shiny spots. Rest of bearings still have there orignal coatings intact. All bearing had .002 clearance when checked. Any ideas? Crank bore? Poor crank grind? Was hoping to get motor together this weekend but now not so sure.
 

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Bent crank or needs align hone/bore. Machine shop time. Check crank first.
 

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1969 Camaro SS350
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Discussion Starter · #3 ·
Crank just turned 010 rods and mains. Should or would shop have noticed when doing the work? Have tools coming later today to do some crank measuring
 

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Likely block line bore/hone. I know of one motor that has similar wear that was put together years ago and still running after a cheap refresh(not a performance application)
 

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.002 clearance is pretty tight for mains IMO, how did you check clearance? Plastiguage lies, it just gets you close. I always use dial bore gauge and mics that measure in tenths of .001.
Block probably needs align hone the way it’s scrubbing those bearings. If the crank is straight then good chance main saddle bores are out to lunch. Production blocks are all over the place.

Mike
 

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Crank just turned 010 rods and mains. Should or would shop have noticed when doing the work? Have tools coming later today to do some crank measuring
Should have checked for straightness. Could be the block, should have been checked also.
 

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1969 Camaro SS350
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Discussion Starter · #7 ·
Took a bunch of measurements yesterday and looking for a site that has runout + or - for crank mains. and rod and main tolerances + or - Crank has been turned 10 10 rod and mains. Might need a little help from you guys pointing me in right direction. My brother is x-engine builder , aerospace machinist. had all the fancy tools to take measurements. Gave me a lot of dimensions and said now do some homework
 

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Personally I don’t like to see more than .002 on center main for runout with .003-.003.5 bearing clearance. I prefer .001 runout but most crank grinders can’t give you that.
I think the gm specs is probably more . If you think about it if you have .001 runout on .003 clearance it is only . 0005 tenths on each half of bearing shell.
As far as journal taper maybe .0003 tenths to .0004 tenths . Main bearing housing bore size the spec is 2.604-2.641, I pretty much put everything at maximum 2.641 to get .003-.0035 bearing clearance. JMO

Mike
 

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Discussion Starter · #9 ·
Lets see if I can get this right. Runout on mains, worst one was .00075 rest were less than that.
Average on rod journals 2.0891
Average on 1-4 main journals 2.4391
#5 main 2.4385
Didn't write journal taper down but brother said it was good.
Plastic gauge mains 1-5 all .002
Didn't get a main bearing housing bore diameter
Think I've got this posted right, if not will try to correct it
After my brother came up with all these numbers said get it line honed. Call tomorrow to get it set up.
 

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Interesting who ever ground the crank put the rods almost on min size & the mains almost on max size.
I would have the machine shop see where the main bore is now, I bet it’s mid size Or closer to min. Maybe put it on max so you gain some main brg clearance. Like I posted .002 is to tight. It would be better if you had at least .0025 if not .003 on a street application. Again JMO.
Mike.
 

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Check opposite bearing bearing shell is seeing if its shiny on opposite side - block bore problem, or,
shiny on same side - journal may be taper ground - one side larger than other side.
 

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Discussion Starter · #13 ·
Check opposite bearing bearing shell is seeing if its shiny on opposite side - block bore problem, or,
shiny on same side - journal may be taper ground - one side larger than other side.
Bearing shells in photos are from block show more polishing I guess you would call it than shells in main caps. Main Cap bearing shells opposite one in pictures have slight polish area but not close to there other half. Almost exclusively #2 and #4 on crank mains.
 

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Discussion Starter · #14 · (Edited)
Brought block, crank, bearings & measurements we took to machine shop. Owner checked crank for straightness, was OK not bent. Checked crank bores with mic they all measured to the minimum. That with the crank measuring towards the max specs convinced him to suggest .009 bearings instead of .010 bearings. He's going to throw in bearings, check measurements and if no good then goes into line hone. Either way said I would have it by this Friday.
 
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