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Bearing damage analysis

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Bearing damage analysis

Postby R.Brown » Fri Apr 06, 2007 10:55 pm

Hi,

I dyno engines for a few shops, and ran a pontiac for one of them on Tuesday that destroyed some bearings. I would like to get some opinions on what caused this...as I am very curious myself.

The engine is a 400 pontiac block, with an EAGLE stroker crank, not sure on the stroke, CID ended up around 450. Eagle H beam rods, and an SRP piston. bearing clearance from their records was .0024 rods, .0028 mains, a Clevite H series rod bearing (BBC size) and P series half groove mains. The crank is cross drilled out of the box.

Engine fired up right away on the dyno, oil pressure was 60 PSI. Has a hyd roller cam, so after 25 minutes of running oil (rotella 15-40) was dumped and the filter inspected. Filter looked like a bit more than average for debris, but not enought that red flags needed to be raised.

Started making some power pulls, 3200-5500, watching the usual stuff. Timing was set at 32, the a/f ratio was 12.3, and the plugs looked fine. This dyno has full exhaust, so you can hear the engine quite well, no noises from the engine during any pull... BUT.... Oil pressure was going from 60-55 during this sweep. That was strange, but not a show stopper. It was not like what you see when the oil is too full in the sump (this is a stock pan, with some sort of windage tray). Oil temps were fine, maybe gaining 3 degrees during each pull, temp measured in a modified oil pan drain plug I use.

Made 3 pulls, power was repeating nice, 580 tq, 520hp. Then after a check for leaks, the next couple of pulls, the engine lost 20 ft/lbs across the board, but the oil pressure and the oil temp did not show a change.

I rechecked timing, and also the Wide band sensors, they were both unchanged. Could hear a bit of noise from the engine when giving it a quick rev, so the filter was removed and there was a ton of bearing material.... end of dyno story.

I had to go into the city yesterday, so I stopped by their shop. It was all apart, and some tremendous damage had occured.

Main bearings 4 and 5 were worn some, but 3 was really bad, 2 was bad, and 1 was just starting to get into copper.

Rod bearings, 1 and 2 were not too bad, but 3 thru 8 were absolutely pounded.

I took some pics and they are here:

Image

Image

After seeing the damage, I was amazed that the engine was not hammering really bad. The oil pressure from the first pull to the last was within 3 psi.

Any ideas from the minds here is appreciated,

thanks,
rb
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Postby Strange Magic » Fri Apr 06, 2007 11:38 pm

Your main and rod bearing clearences are extremely tight. You mention "stroker"? Did someone take a factory replacement eagle crankshaft and offset grind it to increase the stroke? Is this a steel crank or a cast crankshaft? The decending of your oil pressure up on a pull should have drew a red flag and you should have stopped immediately until you diagnosed the problems and then corrected it.

Even a well built engine running to perfection would pick up more than 3 degrees of oil temp from pull to pull unless it rested some time between the pulls. Something does not make sense.

The bearings are definately wasted.

A P series bearing in a performance engine is a no no.
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Postby #84Dave » Fri Apr 06, 2007 11:57 pm

The cross-drilled crank could have hurt the rod bearings? That subject has been discussed here considerably. I believe Darin Morgan, and others, has a good physical explanation as to why a cross-drilled crank should never be used on a performance engine? Dave
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Postby John Wallace » Sat Apr 07, 2007 8:46 am

Eagle makes a 3" main, BBC sized rod journal with a 4.25" stroke for the Pontiac.
It's a cast crank. Usually use a 6.8" BBC rod.

I'd say the clearances were too small.
Also check the oil galleys for 'crud'.
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Postby Engguy » Sat Apr 07, 2007 9:38 am

I second the cross drilled crank. Are you sure a beginner didn't assemble it? How clean etc.

Also suspect line bore, interesting the uppper mains have more wear than the lowers? And its offset to one side. Did it appear to be in balance?
Is crank straight?
And how do you know the clearances they say are correct? I don't think it would run 30 plus minutes if the bearins were installed upside down.
Definatly oil film breakdown for some reason. You say oil was dumped, what was put in?
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Postby Baprace » Sat Apr 07, 2007 10:25 am

R.Brown , pay very close attention to the two oil galley plugs / soft plugs behind the camshaft sprocket. I think a Pontiac feeds the bearings from an oil galley to the crank with a feed hole that is connected to the lifter galley, I found debris behind one once and it knocked the bearings out, perhaps some RTV ? Second thing, I do not see why that engine would require much more bearing clearance than it had already except in a maximum effort engine that is run with cold oil temps, the cross drilled crank is not the hot setup anymore but there are many of them running yet, I do like a 3/4 groove bearing in a cross drilled crank at minimum and have run quite a few Chevy's with the full groove mains also but I don't like the cross drilled cranks. Chevy was very proud of that idea years ago, last but not least is there 1/4 to 3/8 oil screen clearance to the pan floor so the engine can get oil ? Hope this helps.
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Postby Ron C. » Sat Apr 07, 2007 10:54 am

Personally for me, the bearings clearances would be to tight, the crossed drilled crank I would not run. You didn't say what weight oil you put back in it, but 40 weight break in with those clearances(??) I assume something of that weight went back in...??

The bottom line is, insufficent lubrication killed the bearings.
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Postby R.Brown » Sat Apr 07, 2007 10:57 am

Thanks for the replies so far fellas... I should clear a couple of things up. I went and looked at the data again this morning. OIl pressure at 3200 was 61PSI then at 5400 was 58PSI.

What I mean by oil temp is that during the pull, it would raise about 3 degrees... so for example at 3200 the oil temp was 175 and at 5400 it was 178. My rational to looking at the oil temp change during the pull was if there was something causing increase friction, the oil temp would show more of an increase during the pull. Obviously, this is not a sound theory, in this case at least.

The crank is an out of the box eagle, 4.250 stroke, with bbc rod bearing journals, sounds like the one John Wallace suggested.

Yes I agree bearing clearances are tight, but this shop thought that .0028 is plenty on the mains. What kind of clearance would you guys suggest. To be clear, this is a street car, wet sump... nothing trick. Would .0038 on the mains and .0032 on the rods get approval?

The thing that caught my eye is how the #1 and #2 rod bearings look not too bad.

15-40 oil went back in the engine, same stuff, rotella T is what they brought.

Keep the ideas coming please,
rb
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Out of Oil

Postby Hardcore » Sat Apr 07, 2007 11:18 am

Your bearing clearance numbers are fine. No problems there.

It did run out of oil however, possibly a pan, pump, or screen problem. Or the whole combination! Lack of oil is what did all the damage.

List the parts used, pump, pan, screen, etc.

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Postby Strange Magic » Sat Apr 07, 2007 12:16 pm

Yes I agree bearing clearances are tight, but this shop thought that .0028 is plenty on the mains. What kind of clearance would you guys suggest. To be clear, this is a street car, wet sump... nothing trick. Would .0038 on the mains and .0032 on the rods get approval?



If the mains have not been line honed than I would highly recommend that you do so. After the line hone process has been completed take all of your new "performance H or V bearings only" and insert them into the saddles and torque those caps on. Check your main journal size with a good and accurate dial bore gauge or have someone that is competent do this proceedure for you. Take the findings and subtract .0038-.0040 for the mains and .0032-.0034 for the rods. Your going to have to use .010 under bearings to start with this time since the crankshaft can't possibly look too good.

You will not have any problems with your bearings if you choose to go by the guidlines set forth above.

P.S. If you would like to take this one step further than you can subtract another .0012 from the above and have Polymer Dynamics coat the rods and main bearings for you.
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Postby Tuner » Sat Apr 07, 2007 1:43 pm

The clearances sound OK to me. The production tolerance when those engines were manufactured was something crazy sounding like .0005 to .0018 and they all ran fine when they were new.

I’ll bet the journal fillet radius is larger than the bearings are chamfered to clear. The oil can’t flow through the bearings to cool them if the side clearance of either the rods or the bearings is too tight. Naturally, there will be normal oil pressure.

The #1, thrust and rear mains look OK because they have an escape route for the oil. The angular damage pattern on #’s 7 & 8 look like the rods aren’t straight but it’s likely the bearings were edge riding. The photos are good but it’s hard to see the edges.

Scroll down this linked page.
http://www.carcraft.com/techarticles/11 ... ndex2.html
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Postby nich » Sat Apr 07, 2007 2:35 pm

GM crate 502's come, unfortunately, with cross drilled cranks from the factory. They also come with very tight clearances. If I remember correctly around .0012"-.0015" on the rods. A customer brought us one and we increased the clearance to somewhere around .0025". On the dyno, oil pressure exhibited fluctuations during pulls. Everything lived though. We later built another and this time went with factory bearing clearances. This time oil pressure exhibited no fluctuations on the dyno. Possibly because the tight rod bearing clearances helped prevent oil from being centrifuged out of the rod bearings? Niether engine ate the bearings and are still running fine. It's possible that the pontiac's clearance was not too tight, but rather too loose and bleeding off oil pressure. Anyone else ever use tight clearances, by non cross drilled crank standards, on cross drilled cranks?

Also, an improperly cleaned block can very easily be the culprit as has been suggested.

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Postby Milan.. » Sat Apr 07, 2007 5:48 pm

I assembled for a shop about a year or so ago. I build three eagle crank Pontiac's Two 455 and one 400 with a stroker (3 inch mains) all the cranks where ground(out of the box ) on the high side , to get even .002 on the mains , required a high side line hone. There are no + or - .001 bearings for standard main Pontiac's. I feel , all those bearings are big time tight. And most customers will not pay for a crank cut to get the correct bearing clearances. And there might be a little fibbing going on about those oil clearance numbers... Thanks Milan
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Postby sleeper sedan » Sat Apr 07, 2007 10:11 pm

Ryan, here's a thought... It looks to me like there was no pressurized oil getting there, just what ever was "dipped & splashed" and assembly lube is/was present. I'll have to go look at a couple blocks out in storage but wonder if a galley plug (threaded or pressed) was left out during the reassembly process? You may have oil pressure due to camshaft/lifters/filter/and misc. passages etc. and hence pressure and only a 3 degree rise with the remaining oil being "dumped" behind the camshaft sprocket as suggested by BAPRACE. Had the oil gone past/through the rods & mains there may have been a significant rise in oil temp...? Then again, had oil gone through the rod/main bearings you wouldn't be in this pickle.
Bearing clearances numbers, look fine to me. Not a fan of crossed drilled cranks either btw.
One last inquiry, what was the oil pressure during the sweep? Once the engine and oil were fully warmed up was the oil pressure 20-30-40psi and increased with rpm to 55-60psi?
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Postby Strange Magic » Sat Apr 07, 2007 10:32 pm

Just out of curiosity, how many above that swear to the clearences being .0012 per side on the rod (.0024) and .0014 per side on the mains (.0028) being just perfectly fine, have actually built or build Pontiac and Oldsmobile engines that dyno out at 500 plus HP and see frequent bursts of rpms in excess of 5000?
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