gpr

iTrader: (6)

Had a very loud knock in my LS1, pulled it down and a rod bearing spun. Now I'm wondering why this happened, and how do i prevent it in the future? Even after it spun there was decent oil pressure. Is it from over powering what the rod bolts can handle, they stretch and allow the bearing to spin? Maybe some trash got in the bearing?

My other question is do they make oversize rod bearings? I quickly measured the crank with a set of calipers, and it looks like the diameter of the crank is about .010" smaller where the bearing ground into it. I plan on going with aftermarket rods and pistons, but I'm wondering if i can have the crank ground down and polished, then run oversize bearings? If so, does this weaken the crank?

KCS

iTrader: (20)

There's a lot of things that can cause it, so there can be a number of fixes. The bearing companies say dirt and debris in the oil are the number one cause of bearing failures. Lack of oil and too tight of clearances are pretty common too.

speedtigger

iTrader: (16)

Oiling system failing to deliver oil to that journal, contaminants in the oil and the connecting rod starting to lose it's clamping force on the bearing shell due to heat, fatigue or stress can all be reasons for a rod bearing failure. Close inspection is the only way to determine which were at play in your case.

Crankshafts can be ground to smaller journal size to correct surface damage. The LS1 crankshaft can be ground down for use with undersize bearings. Just be sure that the rolled fillet radius on the sides of the journal were not damaged when the bearing failed. Here is a picture that depicts the rolled fillet radius:



Also, make sure that whomever grinds your crank has the proper knowledge and correctly radiused grinding stone so that this area is not ground during the refinishing of the crankshaft.

If that area of the crank is damaged, I would get another.

Toss the connecting rod that had the failed bearing in the recycling bin. Have the remaining 7 connecting rods checked for size and roundness. Since you had a bearing failure, you may consider replacing the rod bolts in the remaining 7 connecting rods. If you do, have them all resized after the rod bolt installation. Some on here may tell you that is not neccessary, but I personally recommend that the connecting rods are always checked and or resized for proper size and roundness after replacing the fasteners.

gpr

iTrader: (6)

speedtrigger, thank you for your advice. I will have to check the radius on the crank, but I'm guessing it is bad. The bearing got flattened out and actually widened to the point it got into the rod next to it. Why is this radius so important? is that what controls how much oil can escape from the bearing? thus regulating pressure etc...

You mention close inspection will help figure it out. What do i need to inspect and look for? I will probably be replacing the crank, rods and pistons but am curious to the cause.

When i get home tonight I am going to retorque the rod cap and check to see if it is out of round. Will probably check the other rods as well.

This leads me to more questions, once going with aftermarket rods and bearings (or even aftermarket stroker crank) do I need to increase the clearances? If so what is recommended? Will the crank manufactures have recommendations on their cranks?

Also if the clearances are increased I'd assume I need to upgrade to either a high pressure or high volume pump. What is recommended for which application? If i stick to running stock tolerances, I'd assume run a replacement LS6 pump?

speedtigger

iTrader: (16)

The rolled fillet radius increasing strength to the crankshaft by organizing the metal's grain structure and increases density around the journals. It is a similar effect to what forging does for a connecting rod.

That may be a little easier said than done. Some experience in inspecting carnage helps in the diagnoses. If you post up picture I would be glad to give an opinion. Many times what is happening on the other rod and main journals gives some insight. Also knowing what was going on when the rod failed can give insight. For example: Was there some high RPMs involved? Was the oil pressure getting lower leading up to the failure?, Did the engine get hot? Was there audible detonation (spark knock) or visible signs of detonation on the spark plugs or on the pistons/combustion chamber? These are all clues.

This takes precision instruments to do this correctly. Many times the more inexpensive bore gauges are too inaccurate or fussy to give good enough measurements. The high quality instuments that professional machinists use like Sunnen gauges will give you much better information.

That is true in general. I just built an engine with slightly larger clearances. About .002" mains and about .0023" average on the rods. This engine has 40+ at idle and 70+ at high RPMs with a Melling 10295 oil pump and 15-40 conventional oil. Oil weight can play a part in the equation too.

gpr

iTrader: (6)

I finally got some pictures of the crank and the bearings. It looks like the crank radius is find and didn't get touched, so I think the crank is okay to be ground down. Let me know what you think.

Looking around it seems as if most people suggest bearing clearances between .002 and .0025" on the mains and rods for an aluminum block. With the larger clearance I was thinking about running the Meiling 10295 high pressure oil pump. Is this recommended with an f-body oil pan? its not going to drain the oil pain with a high pressure pump is it?

thanks for all the help. I want to make sure going back together this thing is built right and won't have issues in the future.

gpr

iTrader: (6)

Here are the rod bearings

speedtigger

iTrader: (16)

Hard to tell from the picture because it appears there is debris on the radius, but that may not clean up on a 10 cut anyway.

Old Geezer

iTrader: (3)

If the .010 you measured is accurate, that crank won't clean and polish at .010. More like .020 is the next dimension for brgs. @.020 under you will be into the lower area of the heat treat.
For the cost of a new piece, I'd trash that crank and start fresh.

KCS

iTrader: (20)

The 10295 probably won't do much. The 10296 is the higher volume pump. I've had one in my Trans Am with the stock pan and never had any problems. You might if you do a standing mile event or something, but I've never heard of that actually happening.

gpr

iTrader: (6)

I believe it was Martin at Tick performance that told me a high volume pump would suck the f-body pan dry, and to not use one... I guess I'm curious when and where should a high volume pump versus a high pressure pump be used?

Looking at the crank and measuring it looks like it will need a .020" cut and polish for it to work properly. I know you can get bearings for this, but at this point I was concerned with the strength and integrity of the crank.....

gpr

iTrader: (6)

I got the rest of the motor torn down and found two more rods with bad bearings. However I have never seen a bearing like this. They are pitted instead of scared or scratched. What would cause this? I’d almost think it was detonation, but the top of the pistons looks fine, and if the detonation was bad enough to cause that you would think the stock cast pistons wouldn’t hold up.

The other odd thing is the bearings that look like this almost seems as they shrunk... If you hold the bearing in the rod the bearing is way too small as seen in the picture. It is the oddest thing i have ever seen.

gpr

iTrader: (6)

No body has an idea of what would cause the pitting on those bearings?

SuperSport01

Pitting of the bearing is usually caused by oil contamination like air bubbles, water, or fuel.

KCS

iTrader: (20)

Normally when you have looser bearing clearances, you will want to use a higher volume pump. More oil gets pumped per revolution of the crank, so oil pressure is increased from idle on up the RPM range, unlike a "high pressure" pump which generally just uses a spring to create higher peak oil pressure.