Yesterday wasnt the best of days...

I've been rebuilding a 5.3 for my jet boat. A budget build but i did save for a dyno run on it.

Block was a LM7 Gen 3 block. That was magnafluxed, hot tanked, cleaned, decked .016" and new cam bearings put in by the machine shop. (very reputable shop). Specs are
Crank was a stock crank ground .010" and 58x reluctor wheel tack welded
Stock lm7 rods with ARP 2000 bolts – torqued to 45 ft lbs from ARP’s website – Not resized but ran for a year and a half previously
Speed Pro Flat top pistons, fly cut .090” intake and .060” exhaust, press fit, Decking block .016” brought pistons to .010” out of the hole
BTR Stage 4 NA Cam (235/242 .621/.595) and matching springs/pushrods
LS7 lifters
Chevrolet performance high volume pump
243 heads milled .030”
MLS .051” gaskets – Quench came out to right about .041”
Victor Jr intake, Holley 750 carb
Engine was not balanced after tack welds/new pistons

Assembled last week and went to the dyno yesterday (also my birthday). The dyno shop I went to I am VERY happy with. I will go back and anything else I ever build will go there also.
They ran it through a short break in cycle, about 2500-3000 rpm varying for about half an hour. I checked the oil afterwards and it looked fine.
We start doing small pulls (again a very reputable dyno shop) and the engine was making some pretty decent power. We did 2 or 3 pulls from 3k to 5k. Then bumped the upper limit to 6k, oil pressure and afr was good. Could have been a little bit leaner actually. Engine was making some decent power, about 400 hp at 6k rpm. Good oil pressure and low timing (24*).

Bumped the upper limit to 6400 and the engine really started to come alive, did 2 pulls and was making in the neighborhood of 420hp on the soft timing tune and rich jetting. However every single run was different, meaning 10 or so difference in hp/tq between runs. This really worried the dyno operator and we started looking into options. Since the oil pressure was great and there was no noticeable knock we though ignition or fuel delivery.

Tried one of his known good (holley 750 xp) carbs and switch ignition controllers. This is when the runs started to get even more inconsistent. Losing as much as 20 hp per run. The dyno operator was very cautious and concerned, so we drained the oil and cut open the oil filter. It looked a little bit metallic, however it didn’t look excessive at this point.

Changed the oil and put a fresh filter on, and engine started great and ran well, still down on power though. We did 3 more pulls, varying the timing now to make sure that it was not ignition. Ended up pulling drain plug and the oil was copper… looked like I struck gold.

Get the engine home and tear the pan off. All the mains look OK other than the bit of copper that went through them. However, 5 out of the 8 rod bearings had spun and were trashed. Theres a picture below.
Looking at the damage, im trying to guestimate what might have happened. I have a couple guesses, im curious to hear if you have any as well.
1. The pistons/tack welds on the reluctor were to much of a difference of weight and just ended up throwing it that much out of balance and the rod bearings failed.
2. Rods were out of round… Im reluctant on this one, because not only were they torqued 3 times but clearances were checked and were in the neighborhood of a loose .002 on average between all 8.
Im leaning towards the balance theory, but im not sure. Ive never had a bearing spin, let alone 5 of them. None of the rods show signs of stress/being hot. And none failed. Just the bearings. Crank is a little crappy but I think itll easily polish out. No grooving, more of a just dirt situation.

Ideas? Could balance cause it?

In all honesty it does not matter because i picked up a low mileage Gen 4 5.3 last night after this happened. But would still like to have an idea.

 

Only your engine builder knows for sure. What were the rods clearance at and do the pistons have any signs of detonation?

 

i built it and 0 signs of detonation

all the clearances were good, all right around .002 - .0025

 

You mentioned arp rod bolts, did you check for roundness? Added torque will distort caps and become out of round

 

How did you measure the clearance>? If you used plastigauge you have your answer.

 

What do the backs of the bearing look like?
What #cylinder did those bearing come from?
Can you lay them out in order of cyl# showing top and bottom halves?

 

hi

I did not check for roundness because I had run these exact rods and bolts for a year and a half on the previous 5.3

Though I'm starting to think this was my problem. Maybe the old bearings were already "worn" to the out of round. If that makes sense

 

Hi

Thanks for the reply

I used two methods to measure

I used mics and snap gauges and also plastigauge just as a final verification

Both came out to the same or as close to the same as plastigauge can show. Hence why I used mics and snap gauges

 

backs of the bearings looks like crap.

I can take some pictures but I've already **** canned all the rotating assembly. I don't remember what bearings were where

 

We're these arps on the same rod as you're last 5.3? Different rods are different after all, some will distort, some will have luck.

I'm also wondering about oil pressure. U spun 5 bearings, that could be due to lack of oiling. Were you watching oil pressure?

 

Same crank, rods, bolts

New Pistons, crank ground .010 and bearings

But the bolts were on these rods and ran for a year and a half before the rebuild.

Watched oil pressure like a hawk. Never dropped below 60

 

Still looks like an oiling issue. What bearings are those?

And you should check to see if the rods were out of round. If so, then that's your issue. Get the rods resized (although, I'd probably junk them - if the bearings are trash, then the rods were exposed to a lot of excess heat).

 

I'm **** canning everything. I picked up a gen 4 for the rotating assembly.

I will check them though

 

More pictures might help, you checked them properly and had oil pressure without detonation no good reason for this. Is there a pattern to the failure like the bearings in the rear look worse than the frt etc? Some thing bad has bit yer azz and you better find it before you build another. Check the crank journals for round etc,you used the rods before so I can't see them being the cause of your trouble. Is it possible machining dust-debris-dirt was in the oil galleries? The rods get their oil last and will get all the crap tossed at them that's in the oil galleries. Post up pictures of the mains.

 

The bearing in the rear do look worse than the others

I know for sure #7 spun, it was the "first" one i found, i started pulling caps from 8 forward.

All the oil galleys were blown out/scrubbed with bottle brushes. And douced with brake clean.

I've read/heard about clevite bearings "pinching" more frequently. Im not sure if thats what happened

There is no exact reason that i can find. Other than possibly being out of round

Ill try to get the rods measured tonight. BUT that'll be hard to tell since theyve spun in them

 

I've seen this before, with no explanations. Turned out guy who assembled the engine, went crazy with the assembly lube, and got oil BEHIND the bearings. Same scenario as yours, with fresh from shop everything.
Backs of all bearings must be DRY AND CLEAN...NO OIL.

 

Well I've heard that before but after the engine is running some oil gets behind the bearings anyway. But getting assembly lube behind the bearings certainly isn't a good idea. There is something telling in the fact the bearings get worse as you go back...........I have to think on this.


Long long time ago back in the 70's I built a engine SBC and being a novice I dipped all the bearings before installing them. I didn't have any trouble with failure BUT the engine did turn very tight by hand. For sure I never did it again.

 

Agreed, I actually clean the a back of the bearings and the housing bores with Acetone. This is to make sure the bearing seats properly in the housing bore.

BTW, my cyl heads are getting worked on in Dawsonville right now. I was just talking to guy earlier today.

 

Untorquing and retorquing the factory GM Bolts will distort the rod bore housing. I've not used ARP bolts on the LS stuff but the Katech bolts in mine only sent the big ends .0003" out of round. Just a few licks/passes on the Sunnen hone made them right again
Your "ran for a year and a half" was most likely with a worn STD/STD crank and worn bearings Now with new bearings and a fresh .010"/.010" grind. Simply measuring from top to bottom is not a true indicator of what's going on.
Lastly I see ZERO reason to run a high volume oil pump
A ported factory pump with shimmed up spring is more than adequate.
You can't pump more oil if you don't have more oil. Assuming you're not running some sort of 8 quart marine type pan

 

I am thinking you are on the right path. I measured one of the spun rods last night, and i had about .003 out of round.

At this point i am thinking there is a damn good chance i got assembly lube on the back of the bearings, and the out of round just didnt jive

I do run a 9 quart oil pan, so no worries with volume.

I went ahead and bought brand new Scat rods for the rebuild, have a low mile gen 4 crank that will be polished and new bearings

Having a good friend of mine who is a professional engine builder check all my clearances for me, as well as check out the new rods to make sure they are round.