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What caused a spun rod bearing?

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Old 06-07-2012, 08:09 AM   #1
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Default What caused a spun rod bearing?

I was driving the car last night, just cruising @ probably 2500 RPM & it started knocking pretty bad. I drained the oil & it was full of metal so I took it apart & Have #6 spun. I just drive it on the street, but when it's time to play I'v been shifting @ 6800 rpm. Any thoughts on what may have happened? Is it a freak occurrenece, or am I just turning it too fast? The engine only has 27000 miles on it from the factory & has 210 lbs of compression in all cylinders except the one w/ the bad bearing which had 170lbs. I'd appreciate some input on where you guys would go from here, I don't really need any more power (but more is never bad!) I'd like to get out of it as inexpensively as possible & as quick as possible, I live in Upstate NY & really only have a few mos to drive every year. Would you guys just turn the crank? or look for a new one? Or is there anything they can do to mine to make it handle the rpms a little better?
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Old 06-07-2012, 08:19 AM   #2
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Oil pressure is most likely the cause. Id have a machine shop look at the crank.
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Old 06-07-2012, 09:38 AM   #3
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Cranks will need to be checked, rod will probably be bad, replace rod, turn or replace crank as suggested by a machine shop.

Some times it happens to stock engines, but when built, improper cap alignment(older sbc) and rod distortion, installing ARP bolts can cause this, but not common, stock or wilder rebuilds need the rods checked, they are usually going to have one to three needing replacement or re sizing, if not done, that can cause the issue.

Low oil pressure should have been noticed even before, but I have ET to spin a bearing on my cam only motors and I hit 7200 rpm.

The LS motors do confuse me, the older SBC engines had cuts in the crank end of the rod, for the bearing to not spin, the LS engines have it, but on matching places onthe cap and rod, this seems not likely to preven bearing spinning, but it does not happen to them any more than any other engine, so evidently I am no engineer.
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Old 06-07-2012, 11:15 AM   #4
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Oil pressure was between 25 & 30 lbs idling, I'm not sure if that low?? Seemed normal to me. Would you suggest a high volume pump when I put it back together? Also, spoke to a machine shop today, he wants me to bring him the block to clean it out, I was thinking I could strip it down & use parts wash or kerosene to clean it out, I just don't want to pay someone to do the stuff that I can. Any thoughts on that?
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Old 06-07-2012, 11:45 AM   #5
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A ported ls6 oil pump from TexasSpeed is the way to go. And 25lbs seems low
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Old 06-07-2012, 11:51 AM   #6
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I daily drive an 07 Classic Silverado w/4.8 and my oil pressure is roughly 45lbs at idle.
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Old 06-07-2012, 01:19 PM   #7
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I had the same issue. I spun the #5. I took the motor in and they checked it out to make sure everything was strait. I bought new main and rod bearings, a new rod, and new rings(optional). I downshifted in to second when I was trying to go to fourth. The stock oil pump should flow at 30 psi at idle. I ended up getting a good deal on an SLP oil pump that pushes 60 psi now. Honestly though, you could clean out the passages in your oil pump and get better psi than to buy another one. It may not be 60 psi but better than 30. Hope everything works out.
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Old 06-07-2012, 01:20 PM   #8
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Oh and if your taking the motor in, dont bother to clean it because a good machine shop will do it for you anyway if your paying to check eveything in the first place.
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Old 06-07-2012, 01:33 PM   #9
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I shim the stockers, 45 pis at idle usually, 100 in the RPM on one. The machine shops usually boil the blocks and they get them cleaner than i could anyway.
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Old 06-09-2012, 05:42 PM   #10
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Thanks everyone, I brought everything in yesterday at the end of the day, the guy ran his finger over the journal & said he was gonna mic it but thought it was probably to much to machine out. Any suggestions on where to get a crank if it needs one? He said he could get a stock one in a day, but couldn't give me a price yet. Oh yeah, and gonna need two rods # 5 & 6 the ones that share that journal.
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Old 06-09-2012, 08:05 PM   #11
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I shim the stockers, 45 pis at idle usually, 100 in the RPM on one. The machine shops usually boil the blocks and they get them cleaner than i could anyway.
Hey Zones, how do you shim a pump to get more pressure?
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Old 06-09-2012, 08:42 PM   #12
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High pressure, not volume.

A spun bearing is usually due to low oil.
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Old 06-09-2012, 08:46 PM   #13
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I personally would look for an lq9 and throw katech rod bolts in it. Mill the 317s.. Will make more power, easy swap, and will be fairly cheap.

There was an lq9 fs a few days ago for a grand..
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Old 06-10-2012, 12:46 AM   #14
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Check the oil pump...the LS I just rebuilt had low oil pressure and I found the cause to be the oil pump, after disassembling and lifting out the gearotor the machined surface below was wiped out causing the lack of oil pressure at idle...
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Old 06-10-2012, 12:42 PM   #15
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Unless I missed it, were the rod bolts replaced with aftermarket ones?
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Old 06-10-2012, 06:18 PM   #16
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Unless I missed it, were the rod bolts replaced with aftermarket ones?
Hey Prorac, I'm the first one that's had the oil pan off it, it just has cam n heads that my buddy put on it in his car. the engine only has 27k on it. I don't know if this is correct or not, but I was tild that the 2002 had better rod bolts in it than the earlier ones. I was looking st oil pumps online & Melling has a pump for $139.00 that is high volume & high pressure, I was thinking about buying that one. Do you think the 2002 needs better rod bolts than the ones that are stock?
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Old 06-10-2012, 06:41 PM   #17
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if your gunna buy rod bolts get arp and since your motor is pretty much stock to upgrade the oil pump shouldnt be necessary just rebuild it stock and mill the heads for a little more compression.

id guess that since the motor has such low miles the crank built up condensation in your bearing and slowly ruined it. such low miles on a older motor isnt always a good thing because all the oil falls to the bottom of the block and everything corrodes. thats why oil actually has a life span in time not only miles
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Old 06-10-2012, 06:57 PM   #18
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The crank can be re-surfaced and I know that it will work with the rods being -.30 and the mains being -.10. I dont know about anymore than that for the mains but you shouldnt go past -.30 on the rods. Someone else might be able to tell you more about the mains but I would guess not too much more than that. And the shop can look at the rods and tell you which ones need to be replaced. I guess I got lucky in that I only had to replace one. Good Luck.
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Old 06-10-2012, 08:45 PM   #19
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Quote:
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if your gunna buy rod bolts get arp and since your motor is pretty much stock to upgrade the oil pump shouldnt be necessary just rebuild it stock and mill the heads for a little more compression.

id guess that since the motor has such low miles the crank built up condensation in your bearing and slowly ruined it. such low miles on a older motor isnt always a good thing because all the oil falls to the bottom of the block and everything corrodes. thats why oil actually has a life span in time not only miles
bwk, the bottom end is stock but it's already got TEA stage 1.5 heads off a 5.3 (862) casting & the cam is a pred Z 230/230 612/591 111+2, turning it almost 7000 rpm. Thats why I was thinking about that Melling pump. The compression ratio with the heads is 10.5:1 . The machine shop told me that he thought the crank might possibly have to be replaced, but wouldn't know til Monday when he can get his mic on it. if that's the case, any suggestions on where to get a crank?
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Old 06-10-2012, 11:28 PM   #20
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http://www.texas-speed.com/p-503-eag...rankshaft.aspx
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