I have just over 14,000 miles on this engine since a complete rebuild. The rod journals were ground 0.010 under and the mains 0.020 under about 5 years ago.

Bottom end started knocking and I pulled the pan (I was driving cross country and drove with this knock for about 12 miles to the nearest town) and found that the cam looked suspect and some of the lifters had stopped rotating. I assumed that the metal from the cam had damaged a rod or main bearing. I ended up trailering it home.

I pulled the engine today and tore it down -

I started pulling rod caps starting with cylinder #1 . . . I work my way along and things look pretty good - This is #3 and is typical of what I am finding.




Bearings don't look bad at all and no signs of metal embedded in the babbit. As stated, this bearing has about 14,000 miles on it - much of which was run at ~2000 rpm with quite a few excursions to 4500 - 5000 rpm. Pretty much all the bearings looked like this . . . except one!


I get a surprise when I get to #5 when I see this.



The two bearing halves were bonded together - so I got a stiff scraper and pried the two tangs away from each other.




SO then I look at the crank journal which for the most part still looked pretty decent until I rotate it a little and clearly see a large crack. The crack had a sharp edge that wiped out the bearing and that is what the knocking was all about.







I am pretty sure that if I gave it a good yank that I could break it off right across the middle of the #5 journal.





Upon close inspection, I see another crack forming across the #6 journal, but the bearing on #6 looks good.

I am extremely fortunate that I didn't break the crank in the block and wind up screwing up my block and rods / pistons.

I am going to grab another 6 bolt 302 crank and get it magnefluxed and balanced. I am pretty sure I have one in the pile.

Anyone every had a crank crack like this? These cracks look like fatigue cracks - I am running a rebuilt 270 harmonic balancer . . . was it just a bad forging? The block / mains were line bored when I rebuilt the motor and the work was done by a shop with a good reputation.

I don't want to go through this again.