Can anyone tell me why the main bearing on my 499 rb look like this? It has 440 source billet steel main caps and ARP main studs. My machine shop fitted the main caps and line bored the mains. The bearings has .002 clearance when Installed.

Looks like de-lamination of the top layer. I would want the clearance at .003-.0035. What assembly lube?

http://kingbearings.com/files/Engine_Bearing_Failures_and_How_to_Avoid_Them.pdf read this info poor balance job, tight clearances,oil break down (alky motor,e-85) etc.

.002 is pretty tight install clearance for a main bearing IMO Cold starts alone (getting the oil there) can play havoc with that tight a clearance. .002" is more appropriate for a rod Bearing IMHO, I typically run .003"-.0035" on a 2.625-2.75" Main bearing.

Needs more clearance. Get around .003"+

Thanks so much for the link, My bearings definately have fatigue overlay. What would cause this. I was supprised how bad the oil looked in the bottom of the pan. There was a little sludge type residue in the bottom of the pan after roughly 100 passes. Could fuel contaminated oil be doing this to the bearings? I'm thinking I need to change the oil more often. I have been running valvoline vr1 20w50 oil. With .002 clearance on the main and rod bearings should I be running a thinner oil? I think I will also switch to synthetic. Any other thoughts would be appreciated. Thanks for the help.

Agreed on too tight and 20w50 is WAY too thick and I don`t run that in anything ever even at my .032+ main clearances and get away w/5w30-10w30 oil forever.............

Is the sludge possibly asembly and ARP bolt lube? I cringe every time when I see guys on here advising running tight bearing clearances like yours on here Those bearings look like they have had the crank almost wiping up against the bearings Not enough bearing to crank clearances I run .003+ on both rods and mains and I always run full groove main bearings with light weight oil, 5W20Wt with those clearances

Looks like fuel contamination and not a clearance issue.We see that a lot with engines that have fuel or coolant getting into the oil.What does the cylinder walls and piston skirts look like?

This engine has deffinately had some cold weather start up also. Would I be ok running thinner oil with this clearance? Also these were clevite bearings I believe and the new ones I installed last night were king. I don't have the pistons in yet so it wouldn't be hard to change the mains now if need be.

The cyl walls and piston skirts had a little very light scuffing. I thought that was maybe from running no air filter and it can get a little dusty at the track.

http://www.summitracing.com/parts/kgb-mb5116hp

These are the new bearings I went with.

Interesting, my #2,4 mains looked like yours. It appears that one of your bearings shows the flaking only on one side, mine look like that. I was running .027"-.028" clearance which I felt was tight. My oil is 5w30 Royal Purple. Rod bearings (.0032") look perfect. #1,3,5 look decent. My feeling is at my power level the crank may be flexing. Block is a Mega-block so the the center bearings are cross bolted. We opened the line hone for more clearance, we'll see the next bearing check.
Doug

These were also the worst ones. The other three don't really show that fatigue coating. They are all the same clearance.

Were these #2,4?
Doug

Why would you switch from a 3/4 groove main bearing to a 1/2 grove main bearing on a motor that will see north of 5000 RPM regularly?
I like my race engine rods to have oil pressure all the time, not 3/4 or 1/2 time
We're nor racing SB Chevys with little tiny rod journals They have a completely different oiling system so the early SB motors could get away with low oil pressure and oiling the rods 1/2 time until they started making a hoop of HP
I hope you will reconsider on your main bearing type choice

How was the .002 clearance determined? Measuring bore with bearing torqued? and measuring crank? Plasti Gauge?

20-50 is not too thick..........I use Valvoline VR-1 20-50 all the time and never have any issues with it, but I don't run .002 on the mains either

Ok so I didn't realize the new bearings were a 1/2 groove rather then 3/4. I measured the bearing clearance with plasti gauge. So now Im just not sure what to do. Do I pull it apart and change the bearings? Just looking through summit I dont see any King 3/4 or full groove bearings. Does anyone know a part number on them? I just did a quick serch befor i ordered the bearings and from what I saw on here most said they recommended king bearings.

Either get or have someone come by w/id mics or at least snap gauges and try to see what that gets ya............