Just wanting to expand my knowledge. What is a "Spun Bearing" and "thrown rod" and what can cause both of these? I've seen these 2 things quite often in the classifieds on peoples used short/long blocks. Thanks in advance for helping a newb!

 

First of all, here are some pictures of LS1 engine bearings. The half moon metal pieces are the rod bearings, the full circle pieces are the crank bearings, I think. And since I don't know how much you know already I will keep it simple. Someone else may come along later with better pictures and explanations.

http://www.google.com/search?tbm=isc...20l900l7j2l9l0.

There are no moving parts in engine bearings like the rollers or ball bearings you might find in a wheel bearing. The bearings fit into the engine block and the smooth bearing race of the crankshaft spins and floats on a very thin layer of oil between the bearing and the crank. The bearing does not move. The tolerances (gaps) between the bearing and the shaft are very tight and depend upon the oil layer to keep both metals apart.

If the bearings wear and the tolerances become too big or the lubrication between the crank and the bearing is lost, the bearing will come out of the dowels or notches that hold the bearing in place in the engine block and it will 'spin' and begin to burn up and melt. The crankshaft grabs it and spins it and disaster follows shortly.

This is a very bad thing and the crank is either ruined or needs to be machined smooth again and you may also need to machine a new place for the bearing to sit in the engine block and go to a larger size of bearing. We are talking about the main crankshaft bearings above.

A 'thrown rod' may mean a lot of different things but usually starts with the failure of the rod bearing that holds the rod to the crankshaft. Rod bearing failure is just like described above. The rod is the arm that connects the piston head to the crankshaft and a 'thrown rod' may become entirely disconnected from the crank and break into pieces. Since the engine is turning at the time the rod will destroy the piston head and maybe even punch a hole right through the engine block.

That's the simple version, hopefully someone will be by soon to tell you about their disasters and have better pictures. I haven't had this misfortune yet.

 

Good explanation.

Like mentioned there are Rod Bearings, Crank Bearings(Main Bearings), and Cam Bearings.

How they work ghardester explaned very well. The lack of lubrication is what will cause failure, cause the Bearing to either sieze onto the surface that it was allowing to move or shred into pieces and get spit out, and eventually tear the **** out of the Journal or Rod it was in.

When one spins it depends on where it is..on a Rod Journal the Crank needs machining, and Rod re-sized. On a Main Journal the Block needs to be Line-bored and Honed, and the Crank fixed. When a Cam does it, Block and Cam need to be fixed. Wth all 3 there will be metal in the oil from the metal on metal friction, and you will definately hear the knock. Main Bearings dont knock as loud..some dont even make a noise, you will notice the pressure loss.

Pretty much whenever it happens, you will be tearing the Engine completely down, fixing the damage, and building a fresh bottom end. Me personally I wouldnt do it any other way.

Ive had it happen to a couple of my engines, my roommates car I heard it start to go and we caught it before it stacked and tore the hell out of the Rod and Crank.

 

so this may be a dumb response, but since it all relies on being well lubricated, is this coming from keeping on oil changes, etc.?

 

it can be a contributor but driving habits and wear are also factors. nothing lasts forever. even ls1s.

 

Exactly. If you beat the crap out of you motor for miles and miles, don't change the oil when you should, etc., etc., this can definitely accelerate wear, which could lead to a catastrophic failure such as a spun bearing or the like. The stock 5.3 in our Suburban went 111k miles before the bottom end was destroyed suddenly.

The terrible thing is, is that it could happen at any given moment. There are sometimes not always signs or clues that lead to what might happen to your motor, it just happens. So, it's just important to make sure that you stay on top of everything.

 

Long story short: It means your engine is f*cked.

 

Haha okay thanks guys!