Its a sb 406 thats giving me a real headache.The main bearings keep failing.It had a stock crank in it and never gave me any trouble until i took it apart last winter to freshen it up.I put new rings, bearings valve springs and anything else that it needed.It started knocking the first weekend at the track.So i took it out and got the crank cut and new bearings and still had trouble.Then i got another block ( had it line honed) and the crank cut again and this time i did'nt stop until a spun a main bearing in the block.Then i said that the crank must be bent and the machine shop is not seeing it in their machine.Now i got a new scat crank and a new dart little m block.Had it running for about 10 minites and the oil is like gold metellic paint just like every other time i had trouble.Both cranks were balanced and everything else looks good when i take it apart.I don't know what to do with this thing,i got a few bucks spent now and can't get no where.Anybody got any ideas about what could be causing this?
P.S JUst found this site about a week ago and i think its great.Lots of good info on here.
Its killing all the main bearing but some are not to bad and the others are all copper.They are clevite 77 bearings and i have the h series bearings in it this time.Its the same combination that i've run for years without trouble.When i rebuilt it last winter i replaced bearings,rings,cam,valve springs and gaskets.I always use mobil 1 5w30 and the rpm is usually kept under 6500.The oil pressre was always good.70 pounds or so going down the track and around 20 hot at idle without trouble.I did change from a 350 to a 400 transmission this winter but i used the same converter.The converter has the proper clearance from the flywheel and slips in and out of the crankshaft freely.The engine runs smooth with no vibrations and still runs the same et.
I forgot to say that its a 7 qt pan with a hv oil pump.The bearing clearance on each build was between 2 and 3 thou.Its not having a detonation problem.Its 11 to 1 with 34 degrees total timing on 114 octane fuel.
Does it eat the back side facing of the trust bearing out? I feel like there is something going on with your tranny/convertor that is causing this.
The last engine you built, are you saying it has gold metal oil before you even go to drive it?
It seems I have seen something like this & it turned out to be a problem in the tranny that was causing massive fluid pressure at the convertor. This made the convertor act like a hydrolic piston & it would shove the convertor forward with extreme pressure after the engine was started. I dont remember the real cause, but it was something that effected the fluid curcuit that causes it to do that way. May not be this causing it , but it is the only thing I can remember happening like this. One of the signs is the first think it wipes out is the back facing of the thrust main bearing.
Is it wiping both the upper and lower bearing shells the same way?
Are you seeing signs of over heating that indicate loss of oil?
Is the bearing damage concentrated on only one side of the bearing shells, like the crank is bent or the journals are tapered ?
Are the bearings showing signs of walking in the main bore on the back side of the bearing shells?
Are the bearings flaking out pieces of metal or just getting wiped.
Have you been thoroughly cleaning up the oil pump and oil passages before you replace the bearings? If you have junk stuck under the pressure relief valve it could be holding open or closed or sticking.
Have you checked to see if the oil pickup is not bent down so it gets sucked to the bottom of the oil pan? Is it so high in the pan it sucks air?
Do you have a crack in the oil pickup tube so the pump does not prime properly and kills the bearings on first fire up? Are you filling the pump with petroleum jelly to help it prime?
I'm assuming your doing the build. How are you measure things? If you are still using plastic gauge, get a dial indicator, micrometers and dial bore gauge set and start looking closer. Make sure the main and rod big ends before bearings are round. Than add the bearings. Measure the crank pins and read from that on the crank and round journals. Use the TQ method recommended with a verified and test Tq wrench. Measure the crank pin on V blocks to make sure it's straight.
All installed bearings you have should open up as you measure from the 12:00 out toward the parting line. if the do not, you have an issue. If they are not round all the way around without the bearings, you have an issue.
You say a main spun? That sounds like something only a thrust problem like Lucky13 mentioned can cause. If thrust did eat the bearing face it would be likely to keep going into the steel shell and then you have steel particles in the oil.
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Hendrens Racing Engines wrote:Main bearing clearance on a 400 main with an iron block should be .003/ .0035 .002 is far to tight and will cause your problems. Bill
I agree, also change to an oil that has not had the zinc (Mobil1)drastically reduced lately.
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