ok so i have a 2000 f250 with a 6.8l v10 4x4 automatic trans, i recently rebuilt the motor and she maybe has 250 miles on her. i developed a lower end knock that sounded like it was in between the motor and trans. so i pulled the tranny and the flexplate had a hairline crack, i thought ok cool so i replaced the flexplate, made sure everything was tight , started her up and same sound. nothing rubbing in between motor and trans. trans is full on fluid and torque converter was inspected.

the original problem when i first rebuilt it was a crank bearing failed and i lost oil pressure. when i rebuilt her i replaced with a new crank w/matching bearings, new rod bearings, new piston rings, new timing chains, basically a complete bottom end with the exception of the old pistons , which were fine.

now with this new problem my oil pressure is a constant 40-65psi with a manual gauge. the knock sounds like a deep knock and it started out just intermittent, then became more frequent . it began only knocking after it was warm, but now does it upon cold start up and continues, it also gets louder with acceleration but then disappears sometimes under a load, then it knocks pretty loud when the you let off the throttle. the only thing i can think of is a failed wrist pin, but they were thoroughly inspected for tolerances, all were fine 250 miles ago when i put the motor back in. running royal purple oil with a motorcraft oil filter.

this problem has me baffled , just thought id get some input before i tore it back apart.

 

using a mechanic stethoscope the sound is loudest on rear cylinder of motor and also on bell housing of trans, but all flexplate and torque converter bolts are tight and locktighted with the brand new flexplate

 

really? no input?

 

What caused the initial bearing failure that required the rebuild? Was it a main or rod bearing that failed?

If a main bearing, did you line bore (or have checked) the main journals in the block? If out of true you might be destroying the new main bearings.

If a rod bearing, did you have the big ends of the rods resized? checked?

 

sounds like something in the rebuild isnt either assembled right or worse yet has failed already.

 

Sounds like it has to come apart again. Normally engines don't throw crank bearings .EVER..Did you find out why? Rod bearing more popular to goe bad..Either way maybe you have a blocked oil passage or something else going on...Bummer..


Dick

 

In all the engine rebuilds I have done, when a rod knock occurs, its the result of a lack of oil welding the bearing to the crank and spinning it around, then it eventually breaks loose and the damage is done. In 100% of the cases , the spun bearing connecting rod, and the one directly next to it, has been damaged and both of them should have been replaced. Also both pistons should have been thoroughly been checked for damage, as well as cleaning all the metal particles from the engine. You have no mention of the connecting rods being replaced.

 

Ok guys come on...yall are not completely reading my post.. the truck spun a main bearing ( crank ) from loss of oil pressure, i had the block vatted, and replaced the crank with a rebuilt one with matching main and rod bearings.. no journals in the block were damaged, only the bearings. Im very detailed when building and engine.

Problem was a wrist pin that failed...the only part i inspected but didnt replace. So it was my deal in the end, but thats ok. If im going to rip it back out im not putting the old engine back a second time

Just buying a performance long block tomorrow

 

who makes a performance long block for the 6.8 ???

link plz.