Keep eating #8 Rod bearing

Fordaholic495 Mon 11 Jun 2018 - 12:58

Engine will be perfectly fine if I'm just cruising around with short bursts of high RPM (6-6500). However, when I make a pass down the strip shifting at 6k holding WOT, it eats the #8 rod bearing every time. All the other bearings look fine. I put an 8 qt Canton baffled pan on thinking it was starving it of oil, but after 2 passes this weekend it's ticking again, bearing is toast. I was going to put another bearing in it, but I need to figure out what's going on here. Just too much RPM for the (NEW) stock truck rods with heavy speed pro pistons? Only ever hurts the one bearing though.
What do you guys think? Maybe I'll end up with a stroker sooner than I thought.

dfree383 Mon 11 Jun 2018 - 13:12

Lean cylinder?

Fordaholic495 Mon 11 Jun 2018 - 13:28

dfree383 wrote:Lean cylinder?

Could be. I had plugs with me and everything to tune it, but didn't get a chance to before it was junk again. First time it happened there were signs of detonation on that piston and all plugs looked lean, so I figured that was it. Starting running 110 and put a 1000cfm Holley DP (80 jet primary, 84 secondary, #5 Power valve primary, #3.5 secondary, pulls 10" hg at idle) on to avoid any chances of that. Second time I thought it was oil starvation, so I changed the pan. I will pull the plugs tonight and see if that one looks leaner than the rest.

Thank you for one possibility!

DaveMcLain Mon 11 Jun 2018 - 14:48

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?

Fordaholic495 Mon 11 Jun 2018 - 15:37

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?

After the first time it happened I tore the whole engine down, cleaned everything, had the crank ground .010, rods trued up with all new .010 under bearings at the machine shop. Put it back together and after a dozen passes or so that bearing was trash again. Last time, I just dropped the pan and put a new bearing in it, did a couple oil changes to try to flush everything out and ran it. 3-4 passes later it's junk again. I'll check the crank and all the other bearings again tonight, but I'm not pulling a head off to get the piston out so I can't really check the rod. I realize this isn't the best way to go about this, but I have enough money into this 500hp motor to build a damn stroker at this point and I've cut it off.

rmcomprandy Mon 11 Jun 2018 - 16:54

Is the rod big end round and the correct size ...? Is it backwards on the journal ...?

Is it a different crank .... does the oil hole in the crank actually go all the way through with no restriction ...?

It may also have something to do with the oiling from the number 5 main journal concerning a restriction in the block.

Fordaholic495 Mon 11 Jun 2018 - 17:19

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.

Lem Evans Mon 11 Jun 2018 - 18:23

I'd change the crankshaft.

Fordaholic495 Mon 11 Jun 2018 - 20:43

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.
Keep eating #8 Rod bearing Img_2312

ED468 Mon 11 Jun 2018 - 20:48

I seen a friends 351w that was doing same thing that the block deck was off side to side and sloped which with tolerance stack up that piston was like 20+ thousandths out of hole and was hitting head at high RPM and taking out the bearing.

norm Mon 11 Jun 2018 - 21:37

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.

That place looks familiar

Fordaholic495 Mon 11 Jun 2018 - 21:44

norm wrote:That place looks familiar

It's my favorite place lol

dfree383 Tue 12 Jun 2018 - 11:40

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 Tue 12 Jun 2018 - 11:47

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.

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?

Fordaholic495 Tue 12 Jun 2018 - 12:09

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.

Fordaholic495 Tue 12 Jun 2018 - 12:12

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?

I know I just wanted to see if there was anything of concern from what I considered to be a good bearing. Rear sump Canton 8 qt baffled pan. Oil pressure was steady at 50 psi the whole way. No external oil line.

away Tue 12 Jun 2018 - 12:25

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 Tue 12 Jun 2018 - 12:29

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.

It's a stock 460 crank. I have been using it for years, but just changed to these rods/pistons which bumped my compression a good bit. I'm starting to believe it's a tune issue as well it's just crazy how quickly it takes out just one rod bearing and the rest look okay.

manofmerc Thu 14 Jun 2018 - 5:52

One of my 460s did the same as yours except in my case it was #7 I restricted the crossover and afterwards my bearings looked good .And what type of main bearing are you using? half or 3/4 groove .A 3/4 groove will supply more oil to the rod bearing .And you didn't say which oil pump you have .A high volume pump will suck a std. capacity pan dry in no time .Stock pans work better with stock volume oil pumps .As far as detonation after getting all your bearings oil pumps and pan issues fixed back your timing down two- four degrees see what happens then .If you have been using a half groove main bearing going to a 3/4 groove main will give you more oil to the rods.When they were available I used to run a full groove main bearing it seems these aren't popular any more .Funny though I never had rod bearing issues with them . And why not go up two or three numbers on your jetting .You can always lean it down if your engine doesn't like a richer mixture .

dfree383 Thu 14 Jun 2018 - 6:02

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.

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.

Fordaholic495 Thu 14 Jun 2018 - 14:43

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.

I backed the timing down to about 28-29 degrees, but the weird thing is this gives me like 5 degrees of initial timing. I think maybe the curve in my distributor is just wayyyy off and it's advancing too far for my app. I drove it last night with the timing backed off and it still sounds like its pinging. I put the timing sticker on the balancer so that is another thing that could be messed up I suppose.

I have MSD 6al ignition, blaster 2 coil, duraspark dizzy with vac advance (plugged when checking timing). Pistons have a 15cc dish I belive. Rear main started leaking last night so I'm about done with this thing. I have a 552 stroker being built right now so I may just park the truck until that shows up. I'm done playing around.

stanger68 Fri 15 Jun 2018 - 18:18

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.

Fordaholic495 Tue 19 Jun 2018 - 12:06

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.

When I pull the engine out I may very well do that, just to figure out what went wrong. Right now my carb is in the mail being sent to Scotty so he can dyno-tune it on the new 552, so I can't even drive the truck anyway. I still think this engine is a great combo, but it's just not enough power for what I want & I'm tired of running 110 so it's going to sit until the new power plant shows up.

I appreciate everyone's input and when I tear into it, I should have a better idea what happened here! In the meantime, if there is anybody looking for some fresh D0VE heads or any other parts of this motor, let me know!

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