LS1inNM

Im getting ready to have my engine torn apart to replace what we are thinking are broken bearings... a friend of my dad was saying that you dont have to take the motor out and machine the crank... he was saying to just drop the oil pan and replace those broken bearings... im thinking this sounds wrong.... to draw a pic for you guys.. this all happened after a few high way pulls against my friend's evo... the very last race we were going for was off of a roll on a street and I screwed up and down shifted by hand the auto tranny... when it was time to go to 2nd... the tranny stayed in first and just started bouncing of the rev limiter...also had alum shavings in oil... MY question is.. it does have to be opened right.. not just replace the bad bearings

Engine_HP

iTrader: (1)

remove the engine take it to a machine shop and do everything correctly.
crank might be scrached from the broken or spum bearing.

LS1MCSS

iTrader: (18)

Your friend is incorrect. If you spun a bearing it needs to be torn completly down and have the crank turned. Rebuild the entire engine.

scites

iTrader: (30)

you can just replace the bearings but god knows how long its going to last and what it will tear up the next time round.. i had a 79 bronco 4x4 460cid back in the day and it would spin rod bearings so eveytime id get a bearing .002 and throw it in there..always lasted about 4 or so months..but i thrash the **** out of just about everything..

crainholio

iTrader: (2)

This is true, for farm tractors.

99blancoSS

iTrader: (115)

We dont even use the block if had a spun bearing.

brad8266

iTrader: (23)

That doesnt make much sense. Whats the idea behind that?

crainholio

iTrader: (2)

You'd want to understand the conditions present during a bearing failure. The bearing gets hot enough to weld itself to the crank, and then spins inside the block's bearing saddles.

On iron blocks, it's common to see the metal discolored from the temperatures reached during the failure.

When a block is locally heated and annealed in this manner, it's scrap.

99blancoSS

iTrader: (115)

Sorry let me clarify, more than often than not on an ls1 aluminum block when it spins a bearing on the ones we've found it was better to not re-use the block. Sorry for the confusion.

brad8266

iTrader: (23)

Why not reuse the block? All it takes if you spin a main bearing is a simple align hone to the block and mains if they are smeared or nicked up at all.

crainholio

iTrader: (2)

Post what you know about heat treatment and annealing of aluminum and we'll go from there.

landonew

I pulled the motor out of my car, had the crank spun, installed new bearings and rods and dropped her back in. Probably not the best way to do it, but it was pretty cheap considering the alternatives.

BTW, I would definately suggest buying a forged shortblock from one of the sponsers in lui of this. I just didn't have the coin at the time.

2000_SS

iTrader: (24)

even though it's different, its the same in the case of what we do where i work: we make feedwater heaters, MSR's, condensors, ETC...basically heat exchangers for powerplants. once a certain part is completed and bought off by inspection, it's released to go into the stress oven. all the welded parts are brought up to a certain temperature, and allowed to cool back down SLOWLY. once the stress process has been completed, we aren't allowed to weld anywhere on a stressed part because it will eventually lead to failure of the unit.

the principle is the same on an engine block, when you apply lots of heat to one specific spot (like a bearing spinning), without doing the same to the rest of the block, it will be weakened drastically in relation to the rest of the block. the fact that it's an aluminum block (with steel main caps as well) would amplify the effect somewhat. it would probably be difficult, if possible, to detect with a magnaflux test. an ultrasound would be the only way to see. the microstructure of the metal is permanently changed. it's the point where the affected metal and unaffected metal meet that can cause failure.

brad8266

iTrader: (23)

Is this the heat treatment expert I am speaking to or something?

brad8266

iTrader: (23)

The OP more than likely spun a rod bearing not a main bearing. Spun rod bearings are way more common on an LS1 than spinning mains. Spinning a rod bearing has no affect on the block.

crainholio

iTrader: (2)

Your posts are kind of amusing when read in series.

Engine_HP

iTrader: (1)

^^^^^^ correct

99.9percenter

iTrader: (2)

I had a burnt(not spun) rod bearing with severe rod knock. I dropped the pan removed the cap and stoned the crank by hand. 15 hrs.! Motor was fine lasted for years. This is why I don't run thick oil any more. 20w-50 is what burnt the bearing.

crainholio

iTrader: (2)

Which is why Bondurant Racing School runs Mobil-1 15W-50 in their fleet of LSx engines, they like "burnt" bearings. Whatever "burnt" means.

Paint_It_Black

iTrader: (1)

They probably run tolerances loose enough for 15w50 though. If they're a racing school they know better Sounds to me like 99.9 put some 20w50 in a stock bottom end. Which at cooler temperatures MIGHT be too thick to properly oil the bearings. Especially if it was run hard before the oil temp got up to 160+.