engine and drivetrain spun bearing....

[gone002]

ok need help here

rebuilt engine like 1 yr ago

since then only like 2hrs running time

(been working on the e30)

i pulled the engine because of a crazy knocking at low idla

turns out bearing 1 and 4 are shot!

4 is like half as thick as it should be

the little tabs that hold it in place broke off

and 1 is spun and stripped down to the copper

any thoughts on how and why this happend?

and is my crank toast?

[john_a]

Cranks looks bad, I'd find another. These cranks are pretty durable unless someone goofs up the works, so there's plenty of used ones to pick from.

What went wrong here is hard to tell without knowing more details, but it looks like the oil film was wiped out on those rod journals. This is sometimes seen shortly after a rebuild where someone tossed in new bearings without proper measurements. Using Plastigauge does not count, that is no substitute for measuring the big end bore of the rod to ensure it is not pinched tight across the parting line.

The BMW rod is pretty stout, but the bearing bore does stretch in the thrust axis which will make tight across the parting line. The shape changes from round like O to narrow 0, and because of where the Plastigauge reads clearance, you don't find where it is too tight when the old worn bearing is replaced by a new bearing shell. New shell at full thickness in a pinched bore wipes out the oil film even though the Plastigauge showed OK clearance.

Of course, there's pleanty of other things that could have gone wrong. But if you do not check the rods & recondition them as needed, this can be the result.

How clean was everything going together?

How was the oil pressure?

[aa/fd]

I believe the previous post covered most of the important and obvious details on why you can loose a rod bearing.

I especially endorse the recommendation of not utilizing "plasticgage" as an absolute to determine correct clearances. It is simply not a substitute for measurement with proper instruments.

Another possibility is the main bearing clearance was way more than allowed, hence little or insufficient oil supply to the rods.

Or simply a dry start-up with no assembly lube and or no system pre lube.

[gone002]

Or simply a dry start-up with no assembly lube and or no system pre lube.

i used lucas all over during assyemble...

[gone002]

[quote="bearings without proper measurements. Using Plastigauge does

How clean was everything going together?

How was the oil pressure?

does platigauge = bullshit calipers? didnt use those i got starrette

however i didnt measure the bearings out of the box...really didnt know i needed to

oil pressure? is qusetionable ...stock gage took a dump long ago

i have a vdo that runs anywheres from 20psi to 40 psi

clean? well not in a hosiptial but the best i could in a drive way =)

[c.d.iesel]

....and take us back in time - WHY was the motor 'rebuilt'

in the first place ?

prior abusive behavior?, over heated?, lubrication problems?,

reused old oil pump?........... ?

o-rings for oil pump old?leaking?cut on assembly??

crud in oil passage?

blocked oil flow?

take your pick

you need to give more details to get more accurate

cause and effect , solution

[gone002]

....and take us back in time - WHY was the motor 'rebuilt'

in the first place ?

prior abusive behavior?, over heated?, lubrication problems?,

reused old oil pump?........... ?

o-rings for oil pump old?leaking?cut on assembly??

crud in oil passage?

blocked oil flow?

take your pick

you need to give more details to get more accurate

cause and effect , solution

quote]

wow i had to think about that for a minute...

i had a catastrophic failure of the front pully ( in other words the front pully came off)

caused the crank to warp...

cracked the keyway and jammed up the crank

i decieded it was a good time to go through the whole engine...

i cant really recall when the oil pump was replaced....its out of an 84

from the outside its in good shap. not so sure about the internals...should i rebuild it? is that possible?

and yes over the years i have been gulity of all of the above charges...lol =)

thanks for the diagram btw

[Guest Anonymous]

an additional small point: when you put it back together did you keep the backs of the crank and rod bearings dry? Only the fronts, the bearing surfaces, should be lubricated.

[gone002]

an additional small point: when you put it back together did you keep the backs of the crank and rod bearings dry? Only the fronts, the bearing surfaces, should be lubricated.

honestly i dont think i was that specfic ...

i just lubed everything

so what youre saying is that only the inside of the bearing ( the part that touches the crank) should be lubed and not the outer surface that touches the rod?

[c.d.iesel]

....you DO NOT 'rebuild' the oil pump.

You replace it with a NEW pump.

[gone002]

....you DO NOT 'rebuild' the oil pump.

You replace it with a NEW pump.

quote]

so wait what you are saying is....

[1972fritz]

if you need a crank give me a hollar i got a few here at home. adampybas@ yahoo.com

[gone002]

just read this at :

http://www.aa1car.com/library/ar797.htm

"Misalignment is another condition that can accelerate bearing wear. If the center main bearings are worn more than the ones towards either end of the crankshaft, the crankshaft may be bent or the main bores may be out of alignment."

since 1 and 4 took the dump this would be my best guess..

found this too...

http://www.crankshaftco.com/steel-crankshaft-hardening.html

Nitrided crankshafts can easily be welded and ground without concern. A .010 undersize grind will cause some of the benefits of nitriding to be lost. At .030+ undersize, nearly all of the nitriding benefits are lost. Therefore, it is recommended to have the crankshaft hardened again after grinding.