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Old 08-14-2007, 07:21 PM
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400 sbc wiping out main bearings

hey guys, any help on this would be great. i have a 400 sbc (406) built by a machine shop here in pa and have had nothing but problems with oil pressure and keeping bearings in this motor. everything is new in the motor, eagle crank,6inch rods,rods pistons,balanced, etc. the first time this happened, i had 2 quarter mile passes on the motor. oil pressure would be at 55-60 at idle and 85 making a pass. after the second pass, the oil pressure dropped to 30 and started to fluctuate towards 0. pulled motor out and sent back to machine shop, the main bearing were wiped out but rods not that bad. the machine shop had no idea why this happened(and actually still don't) again, they checked everything out and re-assembled the motor. this past week i got 6 passes on the car and once again oil pressure started to fluctuate.took the oil filter off and it was filled with copper. needless to say, after spending $7000.00 on a motor that i can't seem to get a straight answer from these guys, is really getting to be a pain in the butt..

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Old 08-14-2007, 07:27 PM
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Examine the plugs very carefully for evidence of detonation.
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Old 08-14-2007, 08:13 PM
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I agree with tech, Detonation can take out bearings as well as cause other damage and sometimes you`ll never hear it. The signs on the plug usually looks like small little purple specs. Usually when it`s detonation it wipes out the rod bearings before it does the mains but in the point of detonation there`s no way to know what will go, usually it`s the weakest link. While I`m no one to argue with the machine shop that`s doing the job, are they giving you the clearence specs? anything under .0015 is not enough and anything over .003 is too much.
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Old 08-14-2007, 09:40 PM
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400 wiping out main bearings

hi race140, it sounds to me like your main line is out, did the machine shop line bore or hone main line? look at your thrust bearing that controls end play does that have damage to it? if the rear cap is not square you will wipe out the mains in short order. a lot of shops have line bore/hone equipment, very few do the job right. sam-missle
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Old 08-14-2007, 10:25 PM
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Quote:
Originally Posted by sam-missle
hi race140, it sounds to me like your main line is out, did the machine shop line bore or hone main line? look at your thrust bearing that controls end play does that have damage to it? if the rear cap is not square you will wipe out the mains in short order. a lot of shops have line bore/hone equipment, very few do the job right. sam-missle
exactly what i was thinking or the crank isnt straight. the telltale clue is that the OP said the mains are wiped but the rods are ok, the oiling system feeds the mains first then through the crank to the rods. likely causes:
1 warped/bent crank.
2 mains out of line.
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Old 08-15-2007, 07:25 PM
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probably wouldnt be a bad idea to check the flwheel/flexplate as well as the trans input shaft, clutch etc. The imbalance may not be inside the motor.
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Old 08-15-2007, 08:15 PM
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Bell housing run out is very important also. I had a new rebuild that would wipe the thrust bearing out in 15 min. Changed every thing on front of tranny (torque,pump housing,input shaft,ect) still had the problem until i changed the case out. Is your converter balooning? just some thoughts
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Old 08-16-2007, 11:48 AM
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Have the crank checked Eagles are notorious for crank being ground out of round and tapered.
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Old 08-16-2007, 12:53 PM
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I work in York. If you want a second opinion (or another machine shop) I used a guy a few minutes from York.

Email or pm me if you're interested. This guy collects 400's for his personal use, and he knows his way around them.

P.S. The 400 sbc that came in my car was rebuilt somewhere in York (before I bought it)... It died a similar death... very interesting... I'm very curious who did your machining...
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