2002 5.3 Crank appears to wobble at idle

[rockola1971]

I had a 2.8L v6 slip the balancer in a S10 blazer at interstate speed back in 1996. It broke the crankshaft into 3 pieces.

 

[2006Tahoe2WD]

I had a 2.8L v6 slip the balancer in a S10 blazer at interstate speed back in 1996. It broke the crankshaft into 3 pieces.

Thanks for that. We've now identified the worst case scenario.

 

[strutaeng]

The crankshafts on these engines are made out of nodular iron (also called ductile iron), which a cast iron technically. It's very difficult to snap one of these cranks, unless you are pushing an insane amount of boost, like over 25 psi or something ridiculous and putting out around the 1,000 HP mark.

 

[rockola1971]

The crankshafts on these engines are made out of nodular iron (also called ductile iron), which a cast iron technically. It's very difficult to snap one of these cranks, unless you are pushing an insane amount of boost, like over 25 psi or something ridiculous and putting out around the 1,000 HP mark.

But....they arent made to be out of balance and that is exactly what the harmonic balancer prevents until it doesnt.....once the belt slips between the inner and outer hub. Then all bets are off.

 

[2006Tahoe2WD]

Harmonic balancer is a bit of a strange name. There are some engines that need the main pulley for balancing but most don't. The 5.3 doesn't need external balancing. Harmonic is the key word. The crankshaft has natural rotational vibration frequencies that need to be damped out. The natural frequencies are called harmonics, hence the name. There is "rubber" between the outer and inner part of the pulley. At certain engine speeds the rubber deflects thereby absorbing some of the unwanted rotational forces in the crankshaft.

 

[strutaeng]

But....they arent made to be out of balance and that is exactly what the harmonic balancer prevents until it doesnt.....once the belt slips between the inner and outer hub. Then all bets are off.

I'm not following you. Are you saying that a belt slipping or falling off can cause a crankshaft on the LS engines to snap? I don't really see that happening under regular driving conditions.

On these engines the crankshafts are internally balanced to the rotating assembly. The harmonic balancer is not to balance the engine, only dampens small vibrations (or harmonics). That's why is not keyed in. The flexplate is not indexed either like some of the older engines or had a counterweight on them. Accessories are not balancing the engine either, and are usually only dragging down a small percentage of the engine power.

A lot of the 70s and 80s engines had gray cast iron cranks that were very brittle and these are times before advanced computer modeling such as Finite Element Analysis was developed. Coupled that with externally balanced design, I can see a belt coming off causing issues on those engines.

Edit: typed this last night and now see @2006Tahoe2WD Seems like we are saying the same thing about the harmonic balancer...

 

[OR VietVet]

Had an old 75 K10 pickup. One day the balancer flew off and in to my radiator. I looked and the end of crankshaft was broke away where the key way slot "was" at.

 

[2006Tahoe2WD]

I'm not following you. Are you saying that a belt slipping or falling off can cause a crankshaft on the LS engines to snap? I don't really see that happening under regular driving conditions.

On these engines the crankshafts are internally balanced to the rotating assembly. The harmonic balancer is not to balance the engine, only dampens small vibrations (or harmonics). That's why is not keyed in. The flexplate is not indexed either like some of the older engines or had a counterweight on them. Accessories are not balancing the engine either, and are usually only dragging down a small percentage of the engine power.

A lot of the 70s and 80s engines had gray cast iron cranks that were very brittle and these are times before advanced computer modeling such as Finite Element Analysis was developed. Coupled that with externally balanced design, I can see a belt coming off causing issues on those engines.

Edit: typed this last night and now see @2006Tahoe2WD Seems like we are saying the same thing about the harmonic balancer...

Yes, I think we are saying close to the same thing. I didn't know regarding the keying but it makes sense. Thanks for the added info.

 

[strutaeng]

Yes, I think we are saying close to the same thing. I didn't know regarding the keying but it makes sense. Thanks for the added info.

I just remembered that the ORIGINAL LS1 used on the Corvette WAS keyed in (but strangely not the LS1 of the TransAm/Camaros). I know, that's not a truck, lol. Otherwise none other are keyed in as far as I know.

Some guys do install a pin the crankshaft to harmonic balancer, but that's usually when they add some sort of blower/power adder.

 

[2006Tahoe2WD]

I'm taking the Tahoe in this morning to have the HB replaced. I'll report back. Fingers crossed. I hope it runs truer and maybe a strange noise sometimes at idle will be gone. We'll see.