Anyone knows about weak block on 6.2?

[AWickman]

I just read a thread on www.gmsquarebody.com (6.2 porous block?) discussing the weakness of the 6.2 block. One guy said: "The damper isn't cracking the blocks. The blocks crack because the bulkheads are paper thin. GM made a number of modifications to the outer main bolts over the production life of the engine to try to mitigate it. OTOH, they never changed the damper design. They never solved the problem because it was inherent in the design, and without changing the bore spacing, or putting a huge bedplate under it like Navistar did you're never going to resolve that. Bad dampers will break cranks, but have you ever heard of one causing a block to crack in any other application?" I havent heard earlier that it should be any "built-in" weaknesses in the 6.2 block. My truck had run many 1000 miles and we are just planning a long trip with the camper on the bed. Does anyone on this forum knows anything about weak blocks for the 6.2?https://www.gmsquarebody.com/data/attachments/143/143850-1fcda9cfa81c23daeeca1f3c01ad064b.jpg

[Robyn]

The GM blocks were flawed in several areas.

The composition of the cast iron was not the best. (Early red blocks are supposed to be the best material)
The design of the block is light for a diesel.
As mentioned...the main webs are a tad light.
There are a buttload of stress risers that are were left after machining.


(Sharp edges, corners, bolt holes left sharp at the edges....all this stuff can promote the propagation of cracks)

Large bolts at the outer edge of the main caps just takes away too much material in a critical place.

The block should have been designed with a deep skirt and cross bolted main caps
The crank should have been forged steel from the gitgo

No one thing was the cause....just an accumulation of things that caused issues.

Now...this said...a lot of these engines ran a lot of miles and never gave any trouble.....
The ones that gave good service you never hear about...

[Yukon6.2]

Hi
Yes a bad damper will cause you grief.
Years ago i put new front tires on a Frieghtliner with a 3406 Cat.
I had the hood open,and was changing the tires on the rims without removing the rims.At one point while the engine was running with the hood open and you could see the damper was shot and the engine wasn't idling smooth.This truck had just been bought by a sawmill.I told the owner about it.The truck broke the crank on the first trip with the new tires.
It got parked then sold,new owner replaced the engine the block got damaged too.

[AWickman]

OK, interesting reading. What can one do to prevent an accident? Low rpm and always fresh oil, will that help? Or just cross your fingers?
How can the damper have such an impact?

[JohnC]

How can the damper have such an impact?

Harmonic vibrations can be extremely destructive. Google "Galloping Gertie".

[AWickman]

Google Gallopin' Gertie" shows some really scary pictures for sure. I just cant understand how the dampers relativy low weigtht can hold back and balance the much heavier loads the entire oscillating/rotating mass in an engine like the 6.2 gives.

[JohnC]

All it has to do is change the resonant frequency.

[AWickman]

Yes. Of course. i got the picture.
Thanks for the explanation.

[AWickman]

I have now been reading some more about fluid dampers and I am getting close to buying one. I said earlier that I am very satisfied with my recently rebuilt 6.2, but during the last month, I experience more vibrations. As the texts I have read says an FD will make all the difference. I saw that the manufacturer Fluidampr has two versions. Is it depending on if the vehicle has AC or not (different position of pulley ropes)?
Happy for tips.

[Robyn]

The fluid damper is worth every penny......

Another thing that will kill these engines and nobody really talks about it.

Injector POP PRESSURES that all all over the map (Not equal) cause all sorts of strange torsional vibrations that are not good for things.

This equates to cylinder to cylinder timing that is not equal.....

One cylinder that has a low pop pressure will fire earlier than one that builds pressure longer before the fuel is delivered.

As the injectors wear they do not all wear the same.....

Having a fresh set of "Squirts" put together so the pop pressures are as close to equal is worth a few extra $$$....

Not just in spec, but equal.....makes a very smooth running engine...

[AWickman]

Thank you for that tip too. Im getting more and more convinced that a really well working damper is something that makes these engines run smoother. I have for long notice how different RPMs generate more or fewer vibrations and noise. Some situations the resonance can be really enjoying, and again, it runs smoothly as an inline-six. I will invest in a fluid damper. I will come back and tell about my experiences.

[More Power]

Chicken or the egg? Which came first?

If an engine has a broken crankshaft and one or more broken main webs, can you know with absolute certainty which failure occurred first?

If that engine also has a faulty damper or dampening crankshaft pulley, did the damper/pulley fail because of the crankshaft/block failure, or did the damper/pulley failure cause the crankshaft/block failure?

If you examine dozens of blocks, and see main web cracks in many of them, was it because of thin webs or due to faulty dampers you can clearly see evidence of?

I've personally seen many 6.2L diesel blocks that had hundreds of thousands of miles on them - and they were crack-free with perfect dampers. Luck or ?

I've seen more failed blocks, crankshafts and dampers/pulleys than probably anyone... via pics sent to me over the years and those I've seen personally. Anyone who says they know what causes what is guessing, blowing smoke or just really ignorant. My guesses are better than most, but if I see a broken engine with an abnormal damper/pulley, that's my first guess.

On edit: I also know that a loose flexplate/flywheel, loose torque converter bolts, or a bad two-piece flywheel can also produce huge spikes in impact torque in the crankshaft that can and has broken these crankshafts/blocks.

[AWickman]

Your statements really made me curious. You have seen a lot obviously, but I did get the point (perhaps because English is not my language) Are you telling me/us that no matter the damper, it is other things that matter? Or the opposite? I beg your pardon if my questions are silly.
By the way, I have now ordered a Fluid Damper. Very expensive. Good or bad?

[JohnC]

i think what he's saying is that once the failure occurs, it's hard to tell the cause from the effects, but, many of these engines last a very long time, and they all have good dampers.

[AWickman]

Thank you. My conclusion is then: A good damper is one factor that helps for long life. And a fluid damper should be the best damper one can get with such a price.