Main bearing failure-knock issue

[Huffer]

Built this engine about 4 years ago with all the right parts and machining-
Line honed, balanced, girdle etc.
Engine failed recently, started knocking, disassembled and found main bearings 2 & 3 totally destroyed- we are trying to figure out what happened, car was to the track once and was never really run hard-
My question is related to the knock sensitivity of this engine- old engine, 218,000 miles, ran strong little to no knock running 18-20 #'s on 93 and alcohol-
this engine would knock at 16# with 93 and alcohol-
Could it have been this bearing issue all along that caused the knock?
Hope this doesn't sound stupid!
Thanks, Dave

 

[drturbo69]

Got any bearing & crank pics.
Doc

 

[Huffer]

No pictures- according to the Clevite site pictures, it was either a bent crankshaft or a misaligned crankcase- we'll work that out-
I am really curious about the knock sensitivity. Could the knock sensor have been triggered by the crankshaft noise?

 

[RmvBfrFlght]

I am really curious about the knock sensitivity. Could the knock sensor have been triggered by the crankshaft noise?

Yes, it will pick up bearing knock, even before you can hear it. The knock filter is the brains of the ESC system. It detects a high level of noise in a particular frequency band and signals the ECM.

It also detects a rapid change in frequency, such as when an engine is running normally, then the frequency band of noise suddenly changes. Which is what occurs at the onset of detonation, or in this case, bearing knock.

RemoveBeforeFlight

 

[turbodave231]

That really sucks, Sounds like a crank problem.

If the crank is not completely wasted on #2 and #3 mains, Support the crank with only #1 and #4 main bearings in the block and measure the TIR (Total indicated runnout) on the #2 and #3 main journals. If you have more than .001" TIR, your problem was caused by a bent crankshaft.

Can you post pictures?

 

[pacecarta]

id suspect a bent crank , and yes the knock sensor would pick it up under boost
i had one with 4 steel mains that knocked under boost over 20 psi and it and no amount of alky, octane or timing drop would quell the knock
i didnt build it , it was part of a package deal when my buddy bought a car
i tried to run it but it always knocked over 20psi (still managed an 11.20 on it)
motor had higher compression (195psi on compression test ) so i swapped on a stock set of heads with stock height gaskets and that helped a little
it wasnt until it became a noticable bottom end knock at idle (when the oil pressure was low) that i looked at the mains , and sure enough the #2 #3 had wear , went to pop in another bearing set with motor in car but noticed that the clearance for the top shells wasnt good (bearing shell wouldnt just slide in ) , pulled the motor and got it onto a stand and crank check came up at .001 runout knock mystery solved... bent crank


hard to say wether the crank was bent before you ran it or if the mains werent straight before the crank went in or if you did something to cause it to become bent (detonation) , but a check of the fuel and the alky system should be done before firing up a new motor in that car

 

[SloGN]

The real question is how was the girdle installed. If the caps are not machined correctly to accept the girdle correctly. the girdle can actually cause the main bearing clearances. I actually had this same problem happen to me..

also another big problem with girdles is they are not flat and this causes issues when preloading the oil pan rails using the shims. alway check the girdle for flatness.

 

[Huffer]

I don't think the cap machining was the cause. Jason Cramer did the machining for one of his girdles. I hope you guys are right about the crank causing the false knock. It would explain why the engine ran so poorly.
Thanks for all the feedback.
Dave

 

[SloGN]

I don't think the cap machining was the cause. Jason Cramer did the machining for one of his girdles. I hope you guys are right about the crank causing the false knock. It would explain why the engine ran so poorly.
Thanks for all the feedback.
Dave

when the caps were machined was the caps in the block when the machining process was done? how flat was the girdle how flat was the pan rails. this thing can really affect how the pre-load stresses the cap.

If the motor was just tired and you just rebuilt it. I can't see how the crank got bent. Did you have a serious back-fire after the engine was redone and running in the car. if no i doubt the crank is bent .


Did you spin a bearing or just the bearing are down to the copper.

 

[Huffer]

No backfires or anything unusual. This will be the fourth teardown on this basic build. The first three were to resolve a ring seating problem with Total Seal top rings. Did the whole shim thing with the girdle and everything seemed good. Obviously there was something not right. We'll be checking the crank and block later this week. I have another crank that will go in 10/10.
Thanks again Guys,
Dave

 

[Huffer]

As a point of interest the block was line honed with the girdle and head torque plates installed.
The mains were shedding copper big time.(chunks)