Sooo this one has me a bit puzzled... Foxbody 302 build, has maybe 5-7k miles on it. Re-ring frankenstein build, block I got out of the junkyard and rotating assembly I got from another fox motor. Everything was cleaned properly, crank polished by hand and on lathe, block dingle ball honed, all clearances checked (bout 1.5-2 thou on mains and rods).

Had a vibration develop at 4k plus RPM recently so stopped driving it and took it out. #5 main is toast, all the rods are fine though, none of the bearings look great but #5 is definitely the culprit. Usually with oil starvation a rod dies first so not sure what to think about this one, it clearly is a 50z crank and I had 50 oz weights on the flywheel and balancer... (SB fords have a 28oz and 50 oz external balance depending on year etc)

2 things that stick in my head:

1 - The starter bendix sticks for a couple seconds after starting then retracts... This actually started with the last motor (which blew up) I actually had drilled the starter holes out when I first put this motor together to get the bendix to return properly, just firing the bendix manually with a "lone wolf 3000" it would pop back immediately but when the motors rolling it takes a couple seconds... But perhaaaps it has been shoving the crank into the main during cranking...

2 - I had raced some audi looking mercedes a couple nights before the vibration developed... it was a deep freeway pull soooo it's possible the pan was sucked dry... that said it was full on oil, and I'm only spinning it to 6k on with a stock oil pump and pan... surely stock SBFs can handle 6k with a stock pan/pump right? It's always been my experience though that rod bearings die before mains sooo *shrug*

The .0015-.002” on the mains would concern me, I run more than that on my rods. Remember what Monte Smith always said, “build a loose engine, only you’ll know, build it tight and everyone will know”.

I know nothing about Fords...but did you check the bearing clearance on EACH journal? Crank is straight, yes? So runout was checked and in-spec?

Beyond this, perhaps looking at restrictions in the oil feed is the next place to go? What does that routing look like on the 302? Where in that feed sequence is #5: start or end?

Last, visually it just looks to me like #5 was simply too tight, or there was a pile of dirt that got dumped into that somehow??? (maybe stuff was trapped in the oil feed passage and when things came up to pressure it all went straight out)

The .0015-.002” on the mains would concern me, I run more than that on my rods. Remember what Monte Smith always said, “build a loose engine, only you’ll know, build it tight and everyone will know”.

that looks like crank to bearing rubbing, not enough clearances or not enough oil flow on start up

I think there are 2 or 3 different external balance specs on the SBF, aren't there ?
Never had my stock '89 5.0 to 6,000 - ran out of pull long before that.
.0015 sounds too tight to me, regardless of make & size.

You guys are crazy, .003" crank bearing clearance? This isn't the titanic

You guys are crazy, .003" crank bearing clearance? This isn't the titanic

Says the guy with an engine that ate a bearing.