I R Gunnr

I just got off the phone with my engine shop and it's going to be $1600 to rebuild my freshly rebuilt LQ4, for the 3rd time.
​​​​​The main and rod bearings are wrecked, but other than that the engine survived whatever this issue is. I cannot for the life of me nail down the cause of why a newly built engine could rip through bearings in only 2000-3000 miles. I'm going to list symptoms below and please give any insight you have.

Engine has been reassembled TWICE, the first time this problem was blamed on improper cleaning of the block, which trashed the bearings, opened the clearances, resulting in lower pressure and so on. However, the second set of machine work and assembly was on a new block and done with an intense amount or care to cleaniness and oil priming, by a very reputable shop.

1. Idle oil pressure never below 40, at 6K RPM well above 80.
2. Using melling 10296 high volume pump with correct o ring, no pinching etc
3. Slight valve noise at idle, significant valve noise at RPM (initially blew it off as long tube header noise, don't think it was)
4. Oil pressure gauge always had a 5 PSI tick. The gauge would just bounced up and down 5 PSI, whether at idle or cruise. After a lot of research, I also wrote this off as a normal indication.
5. Oil cooler line had a slight leak, didn't think it was an immediate threat.
6. Small air bubbles on oil dipstick after I knew I had a problem when I found glitter in my oil filter.

Here's my theory: the pump was sucking a little bit of air intermittently. The high volume pump would fully prime, then the increase suction would let air past o ring or maybe in a crack in the pickup(can't find one visually). The pump would momentarily lose prime (the oil gauge tick), but not long enough for the gauge to fall to zero. This cycle would repeat over and over very quickly and the oil was full of bubbles, destroying the bearings and causing lifter noise.

Am I out to lunch thinking you can be sucking air with strong indications if oil pressure?

Going with a new pump and pickup tube this round as insurance. Pic below is a rod bearing.

Thoughts please.

RockinWs6

1st thing you should know the oil pump CAN NOT suck air. What actually happens is air gets pushed into the oil before the pump SOMEPLACE. How the pump actually works is it creates a low pressure area, atmospheric air pressure acting on the oil in the pan pushes the oil into the pickup tube up to the pump. The pump then pressurizes it and forces it out into the block.

So any small void etc where air can get into the oil before the pump can cause trouble. The most likely spot is the o ring at the oil pump inlet. I would add a oil pickup bolt truss that allows 2 bolts to attach the pickup tube. Of course when you get this all together if you see alot small bubbles in the oil you need to go back in and find where air is getting into the oil pump pickup.

Your bearing look like that because they were riding on oily air bubbles. Simply overheats them, you can have 100psi oil pressure but if its full of air its worthless.

Sure signs of a air leak is lots of tiny bubbles in the oil and a noisy top end. The air bubbles in the lifters cause them to run noisy because they are not full of oil because of the air bubbles.

G Atsma

Being that pumps have both a SUCTION and PRESSURE side, if the oil SUCTION tube O-ring is pinched/improperly installed, it will indeed SUCK air into the pump, causing the problem(s) mentioned above. The above is about semantics; YES the atmospheric pressure pushes the oil into the pump, but we laymen call that "the pump sucking oil"

Che70velle

iTrader: (6)

What oil pan are you using? Do you see a lot of rpm and cornering at the same time?

I R Gunnr

Is it possible to still indicate pressure with a suction side leak though? I worked on industrial fluid pumps for a while and they would lose their prime almost instantly if an upstream leak was introduced. Granted they were pulling a suction from 100s of feet away.

Truck oil pan and no cornering and probably never about 5K. I considered the possibility of pumping all the oil to the top of the engine, but don't think it's the case here. The pressure gauge twitch was there even at idle.

G Atsma

You would get pressure, but some of it would be air pressure, with all the bubbles.

gMAG

iTrader: (1)

A similar thing happened to me....once. I found that the O-ring had been pushed onto the pickup tube, too far. The ring should only go as far as sitting ON TOP of the metal ridge (NOT below it) on the pickup tube. Oil pressure had been great until the failure.

RonSSNova

iTrader: (3)

Assembling the pickup into the pump is dirt simple on the engine stand.
hard to believe a guy could screw that up.
I’m assuming the correct Oring was used.

I’d most certainly replace the pump at this point.

G Atsma

^^^This, or the high pressure one. NOT the high volume unless you have DOD/AFM.

RockinWs6

Absolutely, these pumps will not lose their prime. I had 60+ psi and the oil was full of tiny bubbles, Lifters were noisy as hell. I was thinking like you at 1st how could I have 60+ psi and a air leak. After repairing the o ring leak the pressure is about the same but the engine is QUIET.

Another member had 80+ psi and noisy lifters....same deal o ring was damaged. But it the o ring its self may not be the problem, might be the way the pickup tube sits in the pump etc. Like I posted go with a tube truss.


Another thing to know is cold engine oil will have some bubbles in it but as it warms up to normal temp they should be gone. Another simple way to know you have lots of air in the oil is the lifters will never quiet down as the engine warms up. If I were you I would not put load on the new engine until you are sure no air is in the oil. Just run it at idle which will be safe, I drove mine easy until I figured out what was going on for quite a while. But I had a worn o ring which gives a little different symptom's. Mine would start loud them quiet down as it warmed up BUT when the engine was revved above 1500 rpms the air leak would start filling the oil with bubbles. Let it idle for a few mins and it would quiet back down. You just have a LARGE air leak but with new engine clearances you are not seeing a pressure drop like you would on a worn engine with a o ring leak.

I R Gunnr

So along the lines of a worn o ring, here's another theory. I first installed the oil pump using the green o ring from melling. The factory o ring I removed had a kinda squared off edge from being squeezed. The melling o ring also looked like this when I pulled it 10K miles later when I rebuilt the engine, before any of these issues. After the rebuild I used a red o ring, it fit, but not nearly as snug as the melling and when I pulled it was still nice and round on the edges. Is it possible I used an oversized o ring, which ended up just barely crushing the oil pick up neck, so that the factory red o ring made a seal when cold, but once warmed up was just loose enough to let some air get sucked by?

I know it's a stretch, but I can't find any cracks or problems with the pickup tube. I have a new one on the way and I'm going to measure the necks when it gets here.

Thanks for all the input, I feel confident now that is was definitely aerated oil that destroyed the bearings. Now would just feel better if I can really nail down the cause.

Is there any chance of a venturi effect being created downstream of the pump that would suck air? Either internal to the engine or in the oil cooler Iines?

01ssreda4

iTrader: (96)

When I had oil pickup to pan clearance issues (causing cavitation), I had 70 psi of oil pressure but the motor ate the rod bearings in about 20 miles. Never saw any indication on the gauge there was an issue.

I R Gunnr

So the oil pickup was too close to the bottom of the pan? That would make sense for this situation.

bammax

Back in the old days running a high volume pump meant making a few changes to oil passages and bearings so the oil could drain down as fast as it was pumped up. I wasn't sure if it applied to ls engines so I did a quick search and found this link.

https://ls1tech.com/forums/generatio...ease-come.html

tech@WS6store

iTrader: (2)

Stop using the 10296 unless you have need for the extra volume. In a stock build, you wont.
Aerated oil can be an issue as well and agitate issues more esp when used in conjunction with a high volume pump.
How did the O ring look? What pan? What filter?

RockinWs6

Another good point, cavitation will cause big problems quickly. Only thing keeping bearings cool and alive is oil flow, Aerated oil is useless. Be sure to check Pan clearance.

RockinWs6

Hey its possible, I would use the updated blue o ring from GM.

Che70velle

iTrader: (6)

What was your pan to pickup clearance? Good info...

A.R. Shale Targa

iTrader: (2)

Many variables here. Don’t know the clearances and could they have been even larger the second time around even though the block was new since crank had an additional polishing procedure ??
I’m of the belief that you simply can’t pump more oil unless you have more oil
Pan designed for stock volume pump should not be used with a high volume pump. Most builds are just fine with a ported and shimmed factory pump.
Every single street engine I’ve ever seen where a high volume pump was put into a stock capacity oil pan ended with bearings that looked like yours. Within a few thousand miles

01ssreda4

iTrader: (96)

Yes, lifters were quiet and all seemed well. The easiest indicator was a lack of oil to the top end. As oil comes out of the upper galley, it is fed up the pushrods, and down to the rods. Oil at the topend=oil at the bearings. I didnt catch this in time and spun a rod bearing. On a new engine it started doing it AGAIN which prompted me to dig deeper. I found the pickup was on the pan floor. Raised it 1/2", and now the pushrods/rockers have oil slinging out of them.

0. It was against the pan floor.