M series bearings vs Coated V bearings

Hurt an engine badly after changing from micro babbitt bearing to the coated V bearing everyone seems to use now? I have used the micro bearing for years but have been out of racing since the early 90's. Two license passes and blackened the crank and broke three rods. Yes should have looked at the filter after the first one, but really no indication of anything wrong...130 PSI oil pressure etc. Engine is a KB olds, dart big chief, 55% over set back SSI, 25 D timing, dry sump, 300" dragster, lenco, crowerglide. Thanks for any input/advice!

 

My first thought is that its likely not the bearing change. If the M brg was in there it would've happened also.

So something else caused it

My $.02

 

Are you new to blown alcohol engines? Are we talking rods or mains? Where these narrowed bearings? Were you running narrowed bearings before? Aluminum or steel main caps? A block with steel main caps will require different clearances than one with aluminum as the rate of expansion is a bit different between the two. Whenever bearings are coated it takes away some of the oil clearance. Bearing surfaces tend to burn because of not enough clearance, then it touches the bearing itself and spins it, usually blocking off an oil hole or two and starving other parts of critical oil. Check the block and the crank to make sure that they are not broken before you put this thing back together. Do yourself a favor and check the cam bearings for anything abnormal.

 

Not new at all. Been building engines since I was 10 and built them for 30 years for hundreds of customers including many blown alcohol engines. So I am very familiar with bearings, fits, radius's, chamfers, oil clearances etc. To clarify, .0045 on the mains and rods and my question is ; are the coated V bearing as forgiving as the micro bearing?
I realize that no matter what bearing you use, provided it has sufficient, cool, quality oil and don't exceed it's film strength, you most likely won't have a trouble with bearings.....but what if you do? I ran a alcohol funny car in the 90's in Maitland Novascotia at a match race with 10 PSI on the leave and made it to the end and the M bearings looked new!

 

I run a KB Olds block and run the M bearings on the mains and V's in the rods. Never ever had a bearing issue. Ran it both wet sump and dry sump. Made one run with no oil pressure as the wet sump distributor drive to the oil pump jumped out. Rods bearings were worn some but did not hurt the crank and I think it was a Brad Penn that saved me on that one. Do you have the restrictors in for the upper end to reduce flow? If not, it may be starving the bottom end without enough oil no matter what pressure you have. Was the pressure you cited maintained for the whole pass?

 

Thanks for the info. .062 restricers to both sides of lifter galley. Oil pressure fluctuates from 130 at start then maintains approx 85 during run. Running 4th stage scavenge from both heads then into pump then one common line (#16) to tank. I must say 4th stage really must have been moving mostly air/mist. maybe aerating oil?? used a peterson tank w 7quarts and 4 in the pan. Lucas oil. Confusing thing is the 3" babbitt main looked good but the rods were completely delaminated, overheated. The most destroyed bearings I have ever seen.. Yes they were in with the chamfer to the radius and clearance checked with sunnen bore gauge and setting fixture.

 

The rods seem tight to me. I've had them on a new crank be .0055. Even seen a Winberg crank have bearing clearance of .0067. I was told the coated bearings didn't expand as fast as a non coated one. That could of made you have a tight tolerance.

 

Thanks guys for your input. I will make adjustments and try again. However, what is the main reason builders have gone away from the Micro babbitt bearing? They always proved to be a forgiving bearing and in the day, a tuning aid to see how hard cylinders were working.

 

I assumed you were talking rod bearings but then you mentioned thrust?

"ripping the centers out", like as in making the bearings into a full groove bearing?

 

Will, good info. Thanks