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Old 05-15-2011, 11:44 AM
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Spun bearing on 406, but why?

I built a 406 a year ago, and Tuesday, after 450 miles on the engine, it spun some bearings. The rear main bearing looks good. The next cap is where the problem started and it looks like the debris from that bearing cause the rest to fail. Only the bearings under caps 4 and 2 actually spun in the block. The crank and block are both killed and I haven't torn it down to find out what else needs replacing.

I was at about 5500 RPM when the oil pressure suddenly dropped and by the time I was able to slow down and stop the engine was knocking. I had it towed from there, but obviously it was too late.

I have a standard volume oil pump that had no prior issues keeping up with my oiling demands. It appears that all of the bearings, including the ones that spun were still getting oil. The bearing that started the failure looks very bad. The copper is ripped half way off the bearing and is delaminating from the other metal. These bearings were not coated or race bearings, but they were name brand (Clevite).

When I built the engine I checked all of the clearances with a dial bore gauge and micrometer set, then doublechecked with plastigage. All of the mains had .0025 of clearance and the rear main had .0027.

I'll find another block eventually, but this was a virgin 509 casting that I had a ton of machine work done to (bore/torque plate hone, line bore, decked and balanced). If I did something wrong I'm not seeing what it was, but when I find another block, I don't want that one to self destruct either.

Any ideas?
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Old 05-15-2011, 12:05 PM
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Quote:
Originally Posted by Pre-Tuner
I built a 406 a year ago, and Tuesday, after 450 miles on the engine, it spun some bearings. The rear main bearing looks good. The next cap is where the problem started and it looks like the debris from that bearing cause the rest to fail. Only the bearings under caps 4 and 2 actually spun in the block. The crank and block are both killed and I haven't torn it down to find out what else needs replacing.

I was at about 5500 RPM when the oil pressure suddenly dropped and by the time I was able to slow down and stop the engine was knocking. I had it towed from there, but obviously it was too late.

I have a standard volume oil pump that had no prior issues keeping up with my oiling demands. It appears that all of the bearings, including the ones that spun were still getting oil. The bearing that started the failure looks very bad. The copper is ripped half way off the bearing and is delaminating from the other metal. These bearings were not coated or race bearings, but they were name brand (Clevite).

When I built the engine I checked all of the clearances with a dial bore gauge and micrometer set, then doublechecked with plastigage. All of the mains had .0025 of clearance and the rear main had .0027.

I'll find another block eventually, but this was a virgin 509 casting that I had a ton of machine work done to (bore/torque plate hone, line bore, decked and balanced). If I did something wrong I'm not seeing what it was, but when I find another block, I don't want that one to self destruct either.

Any ideas?
It's hard to say whether the bearing failed because the oil pressure dropped or the oil pressure dropped because the bearing failed. The causes of this type failure covers a broad range of potentials from a manufacturing defect of the bearing; through machining or measuring errors of the block, caps, or crank; improper crank balance; failure of the oil pump or system; lack of oil in the sump; and on and on.

The only place I use a stock Chevy oil pump is in stock Chevy GG engines. I have felt, contrary to popular opinion, for the better part of the past 60 years that the SBC oil pump, sump, and pick up is marginal at best so when I build something like a 406 the oiling system gets a lot of my attention.

Bogie
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Old 05-15-2011, 01:32 PM
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Quote:
Originally Posted by Pre-Tuner
I built a 406 a year ago, and Tuesday, after 450 miles on the engine, it spun some bearings. The rear main bearing looks good. The next cap is where the problem started and it looks like the debris from that bearing cause the rest to fail. Only the bearings under caps 4 and 2 actually spun in the block. The crank and block are both killed and I haven't torn it down to find out what else needs replacing.

I was at about 5500 RPM when the oil pressure suddenly dropped and by the time I was able to slow down and stop the engine was knocking. I had it towed from there, but obviously it was too late.

I have a standard volume oil pump that had no prior issues keeping up with my oiling demands. It appears that all of the bearings, including the ones that spun were still getting oil. The bearing that started the failure looks very bad. The copper is ripped half way off the bearing and is delaminating from the other metal. These bearings were not coated or race bearings, but they were name brand (Clevite).

When I built the engine I checked all of the clearances with a dial bore gauge and micrometer set, then doublechecked with plastigage. All of the mains had .0025 of clearance and the rear main had .0027.

I'll find another block eventually, but this was a virgin 509 casting that I had a ton of machine work done to (bore/torque plate hone, line bore, decked and balanced). If I did something wrong I'm not seeing what it was, but when I find another block, I don't want that one to self destruct either.

Any ideas?
Hard to tell what went on and itt would be interesting to see what the other bearings look like, Could be debis for a poorly cleaned block, The oil filter bypass no plugged letting unfiltered oil through the byass and getting to the bearings who knows.

We build alot of circle track engines with standard volume pumps with zero problems, In fact we have one engine with 9 years of racing and nothing has ever been touched since it left the shop 9 years ago and its a top runner in its field.

If your clearances are correct a standard volume pump is fine and the biggest pump we use is the 10% volume from mellings.

You might look at the webbing of the mains and make sure they are not cracked.

Steel or cast crank?? and what series clevite bearings
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Old 05-15-2011, 02:50 PM
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I will check the webbing.

The bearings were Clevite 77 H-Series tri-metal. The crank was a cast GM that had been turned .020 on the mains and rod journals. I bought a set of engine brushes and cleaned with soap, water, and some laquer thinner after it had been machined and hot tanked. Maybe I missed something.
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Old 05-15-2011, 02:54 PM
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Quote:
Originally Posted by Pre-Tuner
I will check the webbing.

The bearings were Clevite 77 H-Series tri-metal. The crank was a cast GM that had been turned .020 on the mains and rod journals. I bought a set of engine brushes and cleaned with soap, water, and some laquer thinner after it had been machined and hot tanked. Maybe I missed something.
Don't clean the inside with lacquer thinner. It is a high energy solvent any that gets trapped in a passage and doesn't evaporate will destroy the lubricating quialities of oil it comes in contact with. Use a very light oil to wash and flush the interior with.

Bogie
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Old 05-15-2011, 03:00 PM
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I did the initial scrubbing with the thinner and then scrubbed it again using soap and water followed by a coat of light oil on all of the important areas. I think I read how to do it in one of the book I have.
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Old 05-15-2011, 03:43 PM
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Be interesting to see what the cam bearings and lobes look like too.
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Old 05-15-2011, 03:55 PM
406cu.in. of tire smokin' fun
 

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I haven't taken it apart any further yet. I'm looking for parts now. The cam is a roller cam, so I hope the lifters are salvagable. I'll look at the cam bearings when I pull the cam.
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Old 05-15-2011, 10:11 PM
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Why do you say the block is "killed"? You think it's trashed over a spun bearing?? Not likely, unless there's more to the story.
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Old 05-15-2011, 11:18 PM
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Which direction was the crank polished? If the guy who did the polishing doesn't know there is a right and wrong direction to polish the crank...you could have your culprit.

I've seen this over a dozen times, usually happens when the crank grinder takes the crank to a different machine to have it polished and its chucked backwards. Usually because the snout makes a good spot for a tail stock center when there is a pilot bearing in the flywheel end of the crank which makes it more difficult to center.

SBC V8 engines rotate CW so if you use a motorized crank polisher and polish it in the wrong direction you get a raised edge that grabs the bearing everytime it fires up and tears a little off. Imagine the crank surface like the scales of a fish, in one direction the scales allow easy movement from head to tail, the other way and you get a sharp edge.

It only happens at startup when the journal is dry, once its running it usually doesn't matter. Might be the reason why it lasted 450 miles before it spun, once the material on the bearing wears off the clearances open up and then you lose lubrication, then whammo you get a spun bearing.

Google the phenomenon, its widely known.

http://www.google.ca/#hl=en&source=h...a234feeac9d081

http://www.enginebuildermag.com/Arti..._polished.aspx
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Old 05-16-2011, 04:50 AM
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Make sure the plug under the rear main cap was in place!!!
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Old 05-16-2011, 05:23 AM
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Since the pressure was good right up until it dropped due to the bearing(s) spinning, I'd imagine that there wasn't anything missing. I'd be taking a close look at the pump pick up, though. If there was a used pick up reinstalled on the new pump, this can allow air to be sucked into the pump because the press fit is never good reusing a pressed in pick up, IMO. What was the distance of the PU off the floor of the oil pan?

In the absence of an obvious cause, detonation may be the root of the failure. I'd be interested in knowing how the bearings now fit into their caps- if the ends of the bearings are above the caps and feel loose, this can be caused by the pounding the bearings receive when under detonation. This sets a mode of failure into motion that can end w/the bearings being spun. This bearing looseness would show up on the rod bearings, too.

If you can show some pictures, it will help a lot. Otherwise, look at the bearings shown HERE to see if you can match yours up w/any of them.

I'd be interested in seeing what (and how much) debris was in the filter. If you're careful you may be able to see what was being trapped before the bearing started shedding metal into the oil, and if it's a large amount of dirt or iron (magnetic) debris it may show you there was leftover junk in the engine prior to start up. There's also the chance that the majority of this could have been trapped in the break in oil filter and was tossed out w/it, but it would be worth a look, in any event- but it sounds like you did a very thorough job of cleaning. Were the cam bearings removed for cleaning?

Usually the mains do not need bored- just honed. Even w/good oil clearance if the crush was insufficient because the line bore and hone was off, the bearings can spin. If they were bored, this has to be done right or the bearing crush can be lost or excessive and this also changes the crank/cam C/L distance and can require a shorter timing set.

These weren't 360 grooved bearings were they? I don't care for them, some do, though. IIRC the H series bearings are narrower to allow for a bigger radius at the crank cheek, but this isn't an issue ordinarily.

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Old 05-16-2011, 07:42 AM
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You didn't say what power level this things was at but it's common to have the caps moving in the registers and spitting out bearings.
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Old 05-16-2011, 03:55 PM
406cu.in. of tire smokin' fun
 

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Let me see if I can answer some questions. I appreciate everyone's input. Thank you.

This was a new engine will a new oil pump. The pickup was welded into place when I got it as it was a oil pan/pump combo from Summit. I did check the distance, but I can't remember what it was off the top of my head.

It has a 276HR cam and 195cc AFR heads. I haven't dyno'd it yet but am guessing around 450hp/475tq.

I'm only running 34 degrees of timing and hadn't really experimented yet with running more. All of the plugs looked go though, so I really don't think detonation is the cause.

I can't say for sure about the way the crank was polished, but I took it to a well known shop who I was referred to by several people.

The bearings looks like they were wiped if I had to call it.

The block has been line honed once already and I was told that you really don't want to do that again. I wondered if maybe there was a problem with the line hone process and perhaps the saddles were excessively ground. It's to late to tell now on the ones that failed, but I could measure the ones that didn't fail if I knew what size they should be.

I don't know how much was in the filter but the pan had an incredible amount of bearing material (chunks) in it.

The cam bearings were removed for the initial cleaning, then the block got machined and new bearings installed, then I cleaned it again with the bearings installed.

The bearings were 180-degree grooved.
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Old 05-16-2011, 04:15 PM
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Of the 'best' bearings that were left in the caps (a relative term, "best"), were there enough left to get an idea of how they now fit into the caps? Have you seen the rod bearings yet? And I'd ask the same question regarding the fit- if it was normal or loose. Detonation might not have a thing to do w/it, but if nothing else you might be able to dismiss it as a cause.
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