67mustang302

So, barely a few months ago I had a thrust bearing fail for no apperant reason. Everything was set and installed properly, never lost oil pressure, don't ride the clutch etc. The only thing I could seem to attribute it too was poor quality oil. This was with the same crank and block that went for over 100k without any oil related issues, it was a lifter failure that killed it the first time(the people that built it used the wrong springs and it floated, when I took it apart I found out they stuffed the #1 piston in too tight and galled the wrist pin).

So, now it has a new crankshaft and new bearings, and I'm running different oil, and now suddenly the #2 rod bearing failed, for no damn apperant reason. Never lost oil pressure, everything installed properly etc. The only commonality that seems to exist is the crankshaft grinder. The same guy ground both the old crank and the new one(journals ground to 2.100 to work with the 5.7 SBC rods) and I had the second bearing failure in about as many months.

I'm starting to wonder if the guy has just got lazy and decided that surface finish ain't important. I'm getting really freakin irritated about this. The only part in common with all the problems I've had so far is the crankshaft, and the only person to mess with the crankshaft has been the grinder. If all the bearings had failed then it could obviously be attributed to a lubrication failure of some sort, or foreign debris, but to have only 1 bearing fail and the rest be fine is suspect.

woodsy

and the bearing clearance was what on that rod?

67mustang302

Around .0025-.003. Plastigauge is only so accurate. Unfortunately I don't have micrometers. I suppose there's the possibility that it may have been too large, but I'm also running a high volume pump, so I'd assume that even with large clearances it should still last more than 2,500 miles. Wouldn't it have to be so excessive to fail that soon with an HV pump that it could be felt by hand?

I just find it highly suspect that since I've gotten engine machining/rebuilding done at a new place I suddenly have these bearing failures. The guy who does the machining on the block seems to do a really good job, but he sends the cranks out to get ground by an older guy that he knows who gives him a good deal. Never had a single crankshaft/bearing related issue for years, and since I've been getting stuff done by this other place I've had 2 bottom end bearing failures in the last 3 months or so. The thrust bearing seemed to make it for about 10-12k mi and almost a year before it went, but this rod bearing lasted not even 3,000mi it seems.

silver91gt

did you prime the oil system for a couple minutes before firing the motor the first time?

woodsy

ya anything over .002 is fine on that 2.100, BUT the problem is not being able to check taper or out of round with out a mic. Got a pic of the bearing?

67mustang302

Oh yeah, I primed the freakin hell out of it right before I started it(also primed it several days prior to that once it was all back together).

I can try and post a pic of the bearing tomorrow, but basically it's fried down to the backing on the upper and lower halves where most of the load is from TDC and BDC direction changes and the power stroke etc. The side of the bearing closest to the other rod sharing the journal still has bearing material, but it has a flaked off beat up look, sort of like fatigue failure, and the side of the bearing closest to the radius on the crankpin is scored and blackened like from a lack of lubrication. There was also a wadded up plug of aluminum from the bearing in the oil passage on the crankpin, so it seems like the bearing started to fail and plugged up the oil hole, which then just starved it.

I borrowed a mic and checked it today, the bearing immediately next to it is spot on, and both the bearing and journal look new, also the journal and bearing that share the same main(and thus the same source of oil) also looks brand new, but I didn't mic that journal, it was totally clean. I also checked the #8 which also had a brand new looking bearing an journal. Haven't checked the other 4 rods or any of the mains, but my guess is that they're perfectly fine. The journal on the beat bearing is around .001-.002 under spec on average, but there's a low spot on one side(the outter end of the crankpin that would get loaded right at the beginning of the power stroke), and that's putting the journal at that point at around .0035 under spec. I didn't check totally for taper, but it seems like there's at least .001 taper on average, and the part of the journal that has the low spot would obviously have around .002-.0025 taper.

The other thing I'm thinking, is that rather than buying the pricey(ripoff I say) Chevy oddfire V6 bearings(aka 331/347 SBF 2.100 rod bearings), the guy who does the block machining took standard King 2.100 rod bearings and cut them on a lathe narrower(just like with the SBC 5.7 rods). That cost less than buying the pricey ones. One of the bearings had a moderate sized nick in it that was rather deep, not right at the edge though, offset from the middle. He said it would be fine, and it did hold oil pressure up until it failed, but I'm beginning to wonder if that nick ended up being a source of fatigue failure for the bearing. The guy who cut them insists that it had to be a result of lubrication failure, even though the other rods I've checked so far look brand new. I don't see how I could have enough of a lubrication failure to totally destroy 1 bearing, yet have others that look new.

mjr46

my 306 when I sprayed it did something similar...wiped the thrust and the nuber 2 main and the rest weren't in bad shape....and my friend just wiped a main the number 4 one to be exact and the rod right beside is = share oiling passage..rest were in great shape.....the two common things we had in or motors was royal purple oil........I was doing some research and speaking with the amsoil rep and royal purple when put to the test on the 4 ball friction wear test was low on the totem pole and failed under heavy stress.......so who knows if that had anything to do with the probs but no more royal purple for me or him

67mustang302

That may be it as well. It seems that back in the day guys could run their engines without oil at all to try and kill them and they would hold up just on the film that was present. But modern oils are sucking severely these days. It may just be the oil. I lost the thrust running Castrol, which apperantly is some of the worst these days, and this rod bearing just went using Valvoline VR1. I've run Mobil 1 in the past and never had a problem with it, it actually ran in the engine that had the half siezed wrist pin and seemed to keep it from totally galling.

94StinkinLincoln

i hate bearing failure, it killed my day when i changed my oil and i said this isnt normal lol

67mustang302

It makes you want to cry. Or in my case, throw a water bottle at the kitchen window. Good thing it was mostly empty and didn't weigh much.