406 SBC eating main bearings! Help!

[Mr408]

I am at a loss. my fresh 406 ate the #4 and 5 main bearings out within an hour of on road runtime....twice now!

The first time, the motor was primed and started, timed etc as normal [solid roller so no cam break-in] run in the garage for half hour or so, oil and filter changed. maintaining 55-60lbs at idle. I went for a easy cruise to town and back, about 30 miles total. On the way back i leaned onit a bit, nothing major, half throttle shifting at 5k and the oil pressure drops. limp it home and dump the oil and its full of bearing material. Out comes the engine for teardown and inspection finding the 4 and 5 mains destroyed. Crank was not scored but copper was transfered on the journals. Checked the crank and measured 5 thou runout!! i could not find anything else wrong, all bearing clearances were checked via mic and bore gauge on assembly. 2 thou rods, 2.5 thou mains.

Engine machine shop was able to straighten the crank and polish the journals. I thouroughly cleaned all the parts and checked for restriction to the mains thinking it was a possible issue. everything seemed good.

I reassembled the engine with fresh bearings, the crank turned smooth in the block and everything went back together smoothly. I went through the startup procedure oil dump the same as above.

Same thing happened again! oil pressure dropped so i limped home and dumped the oil and cut the filter open. Sure enough bearing material was in there.

I have not torn it down yet but i can only assume the mains are out again.

I don't know were to go from here. I have built many SBC and this is a first for me.

Heres my combo
400 4 bolt, studded. fully machined including align honed.
solid roller cam
edelbrock victor jr heads
super victor intake
KB hyper pistons
eagle rods
eagle cast steel crank
fluid damper
fully balanced rotating assy with a balance plate instead of a 400 flywheel.

any ideas??? my first thought is the cast crank flexing under load, but im lost and tired of seeing the inside of this engine.

Please Help
Chris

[zbugger]

My first thought is that the mains oiling passages aren't clean. That, and I haven't really known anyone to shift at 5k after maybe 50 miles. What trans are you running, also? Could it be an issue with the input shaft?

[Mr408]

i thought maybe a blockage or junk in the passage but i yanked the rear plugs and clean as a whisle. the vertical passages to the saddles where clean and clear, cam bearing holes lined up as well.

the rod bearings were immaculate.

[MonzaRacer]

There is a plug that has to be in the block to direct oil to the mains Ill try to find the pic of where it is.
Some machine shops drive them out its somewhere there near the rear of the block.
Ill give my machinist friend a call and reaquire the info I have forgotten.
But there is a small drive in "freeze plug" that has to be there or the mains dont get oil. All so the main webs of previously abused 400s love to seperate from the blocks and the cracks are hidden.

[Mr408]

if the mains don't get oil, either do the rod correct? the first time the rods looked like new. i figured oil starvation would tear the rods out before mains.

I know the small plug you are talking about. its under the rear main cap, its there but i don' t know if they can be driven in too far.

cam bearings where my other thought. the oil holes line up with the feed hole to the mains but i don't know if there is a restriction in the annular groves around the cam bearings. i blew air through the passages with the cam in place and all seemed ok but who knows?

[MonzaRacer]

Yeah its under the main I sort of forgot/brainfade.
If its not there you will have oil psi and oil to cam/valve train but no oil to mains.
Ill dig out a block and double check the depth.

[Mr408]

perfect, thanks.

[Mr408]

added a pic of the damage 2nd time around. #4 wiped out and #5 is starting.

Talked with a reputable builder who suggested align honing the block [turns out my original guy didn't do it because I can use a standard rear seal], and grind the crank.

3rd times a charm

[Steve Chryssos]

......My first thought is the cast crank flexing under load, but im lost and tired of seeing the inside of this engine.

Please Help
Chris

Chris,
"Weird" bearing problems can sometimes be the result of an out of spec crank. The parts come from China and get quality checked. Yours might be a reject that slipped thru the system. The problem is not likely with an Eagle, but it is remotely possible--especially if you didn't get the crank directly from Eagle. Eagle, Scat, all of the brands who buy Chinese cranks will reject bad units and give them back to the original manufacturer. Sometimes disreputable importers will try to float them around to no name discounters at bargain basement prices, who in turn might even go so far as to try and pawn the rejects off as brand name parts.
I'm not trying to alarm you. Just trying to save you from chasing your tail. Have your machine shop make sure the crank (journals, counterweights, etc.) are within spec to rule out this possibility.

[Mr408]

streetfyter68

thanks for the input. the crank is being sent off to a highly recomended crankgrinder tomorrow for a thourough inspection and grind/polish if required/allowable. The block is being alignhoned as well.

I found out after the fact that the imported cast cranks sometimes have poor surface finish on the journals. the builder a spoke with mentioned that he has seen torn main bearings shortly after startup a few times and a micropolish of the crank has always resolved the issue.

hopefully I will 'get it' this time.

[Steve Chryssos]

That Blows! I will sooner go out of business than have my parts made in China. :usa: Keep up the good work. You'll get it right.

[josh@scotts]

whats your clearances on those journals they would have to be pretty tight for it to wipe out the journals that fast and not the others ,just looks kinda inconsistent thats all..

[Mr408]

dial bored and mic'd all mains to .0025". I thought the massive failure on #4 of awful strange myself.

Crank and block went out to be checked by another shop, just heard back today that the main bores were round and alined but my crank is out to lunch [eagle]. took .010" to remove the runout and out of round.

I never even though to check for roundness/runout on a new crank. I just mic'd it to set clearances.

silly me, I figured new parts would be good parts.

[Scott Parkhurst]

silly me, I figured new parts would be good parts.

Well, they should be- That's what you're paying for.

Sorry to hear it! I only run Lunati or Crower cranks for these reasons. I've never had a bad one, and they always check out perfectly.

Will you still run the 'repaired' crank, or are you ready to step up to a forged unit?

~SP~