Keep eating #8 Rod bearing

dfree383 wrote:Lean cylinder?

DaveMcLain wrote:When this happens are you just taking it apart and putting in another bearing or are you also rebuilding the rod each time?  What about the crank journal is it even close to round?

rmcomprandy wrote:Is the rod big end round and the correct size ...? This I can't say for sure as I had the machine shop do everything. I don't have bore gauges to accurately measure

Is it backwards on the journal ...? Don't believe so, but it's easy enough to double check. Never noticed when putting the cap back on last time.

Is it a different crank .... does the oil hole in the crank actually go all the way through with no restriction ...? I have run this crank with other rods and it worked fine. I brushed all of the oil holes out the first time the bearing went and I had it apart.

It may also have something to do with the oiling from the number 5 main journal concerning a restriction in the block. This could be too. Same crank and block I have used for years but not saying it couldn't have gotten restricted recently.

Fordaholic495 wrote:Here are some pics of #4 rod bearing and #8. Also the crank journal. There aren't any grooves in it, but it doesn't look quite right LOL I blew some air through the #5 main to the rod journal with a rag covering it and nothing came out. Not sure what the best course of action is now. Guess I have some thinking to do.
And just for fun, a pic of my bronco and my buddy's truck that I'm trying to outrun.

norm wrote:That place looks familiar

Fordaholic495 wrote:Here are some pics of #4 rod bearing and #8. Also the crank journal. There aren't any grooves in it, but it doesn't look quite right ... I blew some air through the #5 main to the rod journal with a rag covering it and nothing came out.

dfree383 wrote:That’s not an oil starvation issue, probably detonation hammering the bearing out.

You need to put a better tune on it Before you try again.

Paul Kane wrote:The #4 rod is fed by the #4 main; the #8 rod is fed by the #5 main.

Front or rear sump pan? How is the oil pressure behavior while going down the track? Does the engine have an external oil line?

away wrote:What crank is this?  I had the same issue years ago.  I had one of the 1st forged cranks by RPM or something like that.  The story was that the lightening hole in the rod journal was too big causing the material on the journal to be too thin!  This caused the crank to flex at high rpm and take out the bearing every time.  I changed over to the forged eagle crank stuff and never had any problems since.  During that time I did everything I could to ensure proper oiling, good oil pan, pump, cam bearings restricted, crossover galley restricted , bushed lifter bores, oil accumulator etc.... All the bells and whistles......but in the end the crank change fixed it.  

Fordaholic495 wrote:

dfree383 wrote:That’s not an oil starvation issue, probably detonation hammering the bearing out.

You need to put a better tune on it Before you try again.

I have timing set to about 35 degrees total. It's possible that it may be running lean as I haven't had a chance to check plugs at WOT. I really need to invest in an AFR gauge. 11:1 with iron heads and 110 octane fuel I thought I would be alright with that timing, but I'm a newb lol Also, I have a 160 degree t-stat to put in as it runs about 200 degrees down the strip right now. Little warm for my taste.

dfree383 wrote:What’s the rest of the ignition? And have you Checked your timing marks and light to make sure they are accurate?

35 with flat tops is a few more than I’d expect to see be best.

Could have a vac leak too.

stanger68 wrote:Looks like a clearance problem. Correct me if I’m wrong but. Detonation should only get the top bearing not the cap. Plus I don’t think your making enough horsepower to burn one down that bad in one pass from a little detonation. Before I did anything else I’d check rods and crank real good with a gauge.