gapimpin

I had a 383 lt1 in my bird had a forged scat crank in it.
when i was cruisin to austin i noticed a loss in oil pressure then heard a knocking noise "spun a bearing". I shut it down quick and towed it back found my oil pump mounting flange cracked in half and a bunch of metal flake in my oil. figured just needed to rebearing it but when i looked closer i also found one of the bobweights on my crank is coming off.
It isnt completely off but i can see at the base of it where it is seporating from the crank.
anyone else have a problem like this? a few weeks before this happend i found a broken main cap bolt right next to this weight im guessing it was causing a vibration that caused the bolt to break... i didnt notice it at that point in time though.

Bigseth

iTrader: (11)

Sounds like your block needs line bored. Thats probably why the crank broke.

Seth

1989GTATransAm

iTrader: (3)

Who balanced your crankshaft?

gapimpin

I could see improper machining causing the crank to snap in half but i dont think that would cause the bobweight to come off like that.

Balancing was done at a local austin shop with a good reputation for quality.

Bigseth

iTrader: (11)

Thats usually what happens when they need line boring. Here is a pic. Does it look like this?

AC

iTrader: (3)

JEEZUS...is that pic from a mechanical hit or just the out of balance causing such vibration it breaks?

Bigseth

iTrader: (11)

That is from a buddies motor. Block needed to be line bored. No mechanical hit or anything.

gapimpin

mine isnt broken like that it looks like its seporating at the base but has not cracked off like that.

mesterz2889

i hope scat cranks are good thats what i have

Bigseth

iTrader: (11)

Yeah I think your block needs line bored. What were your bearing clearances like? I would definitely pull the crank and have someone check the journal alignment.
Scat cranks are fine. Eagles do tend to balance better tho. But about all of your crank manufacturers stuff comes from China. Unless its a billet crank or something custom. The only difference is where the machining is done. Most all crankshaft failures are due to improper balancing, blocks that require line boring, or loose fitting balancers. Which is mostly the fault of the installer not the crank company. I will say that the few defective cranks I have seen from the main manufacturers, are mainly out of round less than .0001" which is actually in spec. But some people are just too picky. The only bad one I have seen in a while was an Eagle 4" stroke crank that was really a 3.75" stroke. It was boxed and stamped wrong. You have nothing to worry about running that Scat.

Seth