Crank Failures, mainly pre 85?

[john8662]

I just got to thinking of something that sparked my curiousity.

Does the application of the crank dampner pulley used on 85+ engines help reduce crank failures due to less vibration being transmitted from vibrating belts, worn accessories?

If you've had an engine suffer from a crankshaft failure. Post what year it was.

I'm also open to starting a poll if there is enough interest.

[ronniejoe]

There has been much discussion and speculation on this subject...

The damper pulley was designed and implimented to soften crank induced vibrations on the belt to increase belt life...not the other way around.

The one case that Jim showed in his article of a broken crank and broken damper pulley has been incorrectly (IMO) stated as a pulley failure causing a crank failure. In reality, I'm quite confident in saying (again, my opinion, somewhat informed) that the crank failed first with pulley failure as a secondary consequence.

[john8662]

I do agree that belts do last longer with the dampner, got both (82 & 86 models).

I know back in the 80's there was quite a bit of speculation that the 83 models had more crank failures. I know this was right in the middle of the run before the dampner pulley was used. Everything I have stated so far is hearsay though.

Thanks for the input Ron.

[More Power]

What came first, the chicken or the egg? :D

What happened first? Did the crank fail, which then broke the pulley? Or, did the pulley fail, which then took out the crank? These dampening pulleys have significant mass.

Forming an opinion for which happened first sorta depends on how many a person has seen (crank failures), or how many owners with this problem have been interviewed.

Most people who experience it first-hand (and for the first time), usually consider the crank broke first. Only after evaluating many occurances of broken cranks and knowing that almost all of them accompany a failed harmonic damper or dampening pulley, the conclusion becomes a little more inescapable - in that the crank failure was the result an external component failure - be that a failed damper, a failed pulley or a failed flexplate/flywheel.

In addition, most of the broken crank reports I've heard mentioned a low engine rpm at the time of failure. Soon after starting or motoring along at a low power/rpm are most often mentioned. This is when crankshaft harmonics are most affected by dampers, and a low rpm crank failure would have less damaging effect on a good damper/pulley (less inertia/impact).

I only know of one instance where a crankshaft failed and no external component appeared out of the ordinary. In this one instance, was the broken crank due to a cyl block failure or did the crank just spontaneously combust? We may never know... I do know that dampers and dampening pulleys should be replaced if the elastomer appears degraded, or during an engine rebuild. I wouldn't re-use them, but there's always room for other opinions.... :)

Jim

[ronniejoe]

When multiple components are found to be failed in a tear down investigation, several scenarios may be proposed to explain the carnage. However, many scenarios may be immediately ruled out because they do not follow known engineering principles. The remaining scenarios must then be pursued to find the most likely one...all the while bringing sound engineering principles and judgment to bear.

When someone can explain to me how a component with such small rotational inertia as the crank pulley can cause a high cycle fatigue failure in a crankshaft...I might be more inclined to entertain the scenario as valid.

Now a failed torsional damper (harmonic balancer in common terminology) is another story. It has a large ring designed specifically to have high rotational inertia...to damp out high frequency torsional vibrations (which can be and are destructive to crank shafts) in the crank through shear energy dissipation in the rubber ring sandwiched between the inertia ring and the hub. A bad torsional damper can most certainly cause a crank to break.

The comments about low rpm failure are really anecdotal. These crank failures are driven by high cycle fatigue. This requires a load to be applied and removed cyclically several thousand times a minute over a period of time. This type of failure starts as a blemish or material impurity that causes a stress concentration raising the local stress above the strength of the material. A crack has now started. Repeated load applications will slowly cause the crack to grow (increasing in speed the larger the crack gets). Eventually, the crack will progress far enough that the load capacity of the crank is compromised significantly. At this point, the final overload failure may occur at idle or very low load conditions.

A failed flex plate or pressure plate is significant because of the fact that the 6.5 crank is externally balanced. This will cause extremely high imbalance forces in the crank...bad.

Quite frankly, the belt pulley has no impact whatsoever on crank failures. Again, only my opinion.

[arveetek]

Just for the record, my '82 model engine has been ridden hard and put up wet for over 24 years, and it still has the original stamped-steel crank pulley on it. I don't have a large problem with belt life, either. I have replaced the harmonic balancer, though. As far as I know, it has the original crank and camshaft that the General installed in 1981.

Casey

[More Power]

Here's a cut-n-paste from a copyrighted article I wrote a few years ago that relates to this subject.

[B]"All crankshaft harmonic dampers used on the 6.2/6.5 engines weigh approximately 13-lbs. The [I]7-

[john8662]

So...

We've established that a failed dampened crank pulley has the chance of contributing to the failing of a crankshaft due to the pure unbalanced rotating mass of the failed pulley. I do feel as though this is a sound theory.

As to the original question, Do pre 85 engines see more crank failures due to the lack of a dampened crank pulley verses the pressed steel pulley?

I was just curious, but I'm going to say that the dampened crank pulley used on 85+ engines only made a difference in belt life and made no positive influence on crank life. But, when the pulley fails, it has the possibility of leading to crank failure if left unchecked.

-edited to add "dampened" in a few places...

[ronniejoe]

Most of the mass of the crank pulley is in the hub...

The next significant mass is in the rubber itself...

The rotational inertia of the outer ring is small in comparison to the inertia of the damper outer ring.

The only conceivable way that the crank pulley could adversely impact crankshaft dynamics is if the outer ring slips relative to the hub--as mine did--so that the spokes contact the sides of the windows in the hub. This makes a terrible clanking noise. I drove mine for 18,000 miles that way until I finally figured out what was causing it (replaced two power steering pumps unecessarily).

No problems with my crank...I've had it out and magnafluxed since then, too.

[More Power]

Here's one of the articles that appeared here in The Diesel Page about 3 years ago concerning Crankshaft Failures (http://www.thedieselpage.com/members/features/cranks.htm).

We report - you decide.... :D

[arveetek]

I was just curious, but I'm going to say that the dampened crank pulley used on 85+ engines only made a difference in belt life and made no positive influence on crank life. But, when the pulley fails, it has the possibility of leading to crank failure if left unchecked.




That's my view on this subject as well.

Casey

[cucveg]

For performance applications you can buy forged steel cranks for almost any gasoline engine out there. Does anyone make one for a 6.2L?

[Robyn]

Just my 2 cent worth

I have read and agree with the engineering principals refered to by RJ
The secondary issues with the dampened pulley I beleive could contribute to a failure if let go long enough.
One issue for sure is the later rigs were far more quiet in operation.
The earlier units would display a tendency to set up severe harmonics in the long belts. This was a know fact as GM added a skid plate if you will to at least one of the hoses to keep the whipping belt from worrying a hole in the hose.
Once the dampers were added to the pulley setup this anomaly went away.

I have said it before and I will say it again, GM shot themselves in the foot when the chose cast iron for the crankshaft material.

These engines IMHO should have a forged steel crank in them.
I really think a grand percentage of the crank failures would simply have never happened had this been the case.

I have run too many big Gas rats that have put out far more torque and HP and turned RPMs that a 6.5/6.2 would never dream of doing.
I have never broke a crank in any of these engines.

I am also suspect that the cranks in the 6.2/6.5 are the root cause of the blocks breaking. If the crank is flexing or capable of flexing to a greater degree then the block has more work to do to keep it all together.
Now I am not stating that the crank needs to hold it all together but I do believe the issue is with the iron crank.

I recently called a company about getting a Billet steel crank made for my 6.2/6.5 project.
The cost is high but not too bad considering what this could possibly add to the pacakge.

I question Gm's choice in this area because most other manufactures of diesels and any other high output engines use forged steel for the shaft.

I think it was a cost issue and they decided to do it on the cheap rather than make it right.

As some of you know I recently purchased a MIL 6.2 made in 94.
The engine had rods 5&6 gone. The crank was actually tweeked so bad from this that with all the rods removed the crank was still very hard to turn in the bearings.

I have had steel cranks pounded terribly and they did not tweek out of shape to this extent.

Cast iron I think is ok for light output gas engines but diesels need a steel piece thats made of good stuff like 4140-4340 maybe 8620 or some other really tough alloy then if its nitrided to give the journals a really hard surface coating.

Peanut butter does not make good cranks.
What does the cummin have? How about the Stroke?
If memory serves I think they both have steel cranks.

Here lies the issue me thinks. IMHO

Just my 2 cents worth.

Still thinking about spending the $$$ on a billet crank ;0)

Robyn

[More Power]

I heard last June that we may be getting a forged-steel 6.5 crank... ;)

However, in the October 1991 issue of Diesel Progress magazine, Dick Hamparian, who was the chief engineer for the GM diesel engines, said this about the 6.5 crankshaft.


"This engine has really proven the viability of nodular iron together with deep rolled fillets for applications to diesel crankshafts," said Hamparian. "These crankshafts have an endurance limit greater than or equal to induction hardened forged steel crankshafts."

Jim

[gmctd]

Yes - I remember when he made that statement.

I do not find it at all odd that he has not stepped up to the mike, since then............

[Robyn]

I have read that material.
Common engineering principals will however bring to point that a casting especially iron can and does from time to time have areas that are not structurally sound due to eddies and such in the pour.

My real gut feeling is that GM figured as usual that they could build these on the cheap and get away with an exceptable rate of loss and make money.

The Stanadyne debacle was another area that proves that they were more interested in the cubic $$$ rather than producing a quality product.
Now I know the point has been made that Companies like peninsular regularly get 400HP from these engines.

The law of averages says that a good nodular crank will work for some time.
What we are seeing in the failures is most likely the cranks that have internal flaws that cant be seen.

truth be know if you took 100 cranks fresh from the factory and did some good analysis on them you would find internal flaws in some that would result in their demise.

All its going to take is some high stress area to have some eddies in the grain structure or some porosities and you have a failure waiting to happen.
Unfortunately after they break they are so torn up you really cant tell too much.

Forged steel is the gold standard only surpassed by a billet.
Now I know someone is going to take a shot at me on this but thats ok.

I still contend that if the iron was gods gift every crank out there would be made from it.

Who is going to offer a 6.5 steel crank?? AMG ??

Interested for sure I am. ;0)

Robyn

[Robyn]

Here is a nice little tidbit. Nothing wild but good reading
http://www.automotiverebuilder.com/ar/eb010650.htm

[More Power]

Who is going to offer a 6.5 steel crank?? AMG ??


As a rule, OEMs don't discuss future plans. However, an OEM steel crank may be just one item in a number of engine mechanical upgrades. Time will tell. BTW - The proposed upgrade isn't being discussed because of crank failures at the current power/tq level... :)

Jim

[Robyn]

Hmmm
Maybe they should address it at its curent level.

The odds obviously were in the manufactures favor as the number of failures is proportionately low overall.

The overall relaibility of this engine platform will in my opinion be greatly improved with the addition of a steel crank in conjunction with the modifications already done by AMG.With some better heads this engine will be able to reliably produce 325 HP and a buttload of torque as long as the cooling is upgraded too. (Pickup Burb applications)

Just a shame we all could not have rode the golden horse to town.

GM did this same thing with the Olds 5.7. They fixed the fence after the cow got out.

[EWC]

Robyn , care to share the price for the billet crank ?

[NH2112]

The overall relaibility of this engine platform will in my opinion be greatly improved with the addition of a steel crank in conjunction with the modifications already done by AMG.With some better heads this engine will be able to reliably produce 325 HP and a buttload of torque as long as the cooling is upgraded too. (Pickup Burb applications)


I think they also need to add quite a bit of mass to the block and heads, and use 6 head bolts per cylinder like just about everyone else does. It'll necessitate a complete block redesign or a major reduction in bore diameter to gain the room between cylinders, but that 1 bolt will make a world of difference.

Personally, I think it wouldn't be a bad idea to make a 4.5-5.0l V6 with the same external dimensions as a 6.5l for 1500/2500 use. Use an aluminum block & heads for light weight (they'll do fine durability-wise), and taking 2 cylinders out but keeping the same exterior dimensions would allow for MASSIVE mains and that magic head bolt between cylinders. (While they're doing a redesign they might as well put the injectors up top like the 6.9l and 7.3l, too :)) Keep the DMax for 2500HD/3500, and optimize the "MiniMax" for fuel mileage. With modern fuel systems and a quick-spooling VVT it shouldn't be too hard to get 450lb-ft@<2000rpm and 25-30mpg out of this configuration.

[Robyn]

This sounds like a grand idea and sound from an engineering standpoint.

I dont see GM revisiting this arena any time soon if ever.
The 6.5 has issues for sure but with just a couple upgrades it would become a very good platform.

I rant and rave about a lot of the little issues but overall the engine has performed well. We hear all the bad stuff, obviously because this message board is a place to find help when your truck is broken.
Folks dont generally join a forum to crow about the success story they are driving.
As long as the scenery is going by most people dont even think about the car/truck. Its when the thing quits or otherwide has issues that take away from the otherwise normal use of the vehicle that we hear from them.

Overall I dont think the failures that have occured with the 6.2/6.5 platform have been all that great as compared to the engines that have gone a full pull and given their owner a good measure for there dollars spent.

I for one have had 2 rigs that both went down the trail well over 250K and I sold them when they were still running.

The head bolt issue in the current 6.5/6.2 design I dont think is a significant problem to warrant a redesign. The simple addition of a stud kit would make a world of difference.

The cylinder head issues are more related to the alloy in the head as well as the amount of it in critical areas and the coolant flow.

Placing 6 bolts in these heads in my opinion is not going to stop the heads from cracking.

Better alloy and a greater ability to reject heat would go farther in reducing the issue.

The block is not a bad design in and of itself. The issue I believe is possibly the alloy and also the use of the cast iron crank.
I am a firm believer that the iron cranks are, to over simplify, a piece of taffy and are the root cause of the bottom end issues.

When some of us can take a stocker and run it 250K without much issue and then when you pull it down the thing looks near new inside this says a lot.

The failures seem to be sporadic and never consistent from engine to engine.

Some will break a crank, others will lose a head gasket and then next one cracks a #8 cylinder and for each of these failure how many run a good full life without a hitch.

I think the overall cause is a design that has been well thought out but then in implementation has been trimmed down to the bare bones with very little extra left to insure a low failure rate.

All this adds up to one thought process. Cost savings over the long haul.

The company figured on an overall plan and not the short term or small number count as far as a success.

You and I think about "OUR TRUCK" the big boys think about numbers in the tens of thousands or millions of units.

Sure there has been some issues but overall I think the design is a relative success.

With AMG doing things to improve the design and probably other things in the wings we may just see some real enhancements of this package.

I would not hold your breath waiting for GM to revisit this engine. I look to see the D max go away within a few years too.

I dont think we will ever see engines like the small block Chevy again where a design runs virtually unchanged for 40 years.

I think with todays mentality as far as environmental issues and fuel ussage you will se designs come and go on a very short time frame.

It may seem a little off the wall, but I see cars coming with a totally sealed engine that you dont even add oil too or at best thats all you do is add oil. There will be no repair at the local level. Simply run it til it pukes then plug in a new power pack and go again.
The used unit will be either recylcled (Scrapped) or sent back to a facility where it is rebuilt.

I can see the day when you and I will no longer be rebuilding our car at home.
Possibly due to laws governing standards and practices or stupid environmental rules that govern any and all usage and disposal of used engine parts. " heaven forbid you to get any carbon off a piston top strewn about your driveway"

Who really knows what the whacko's will come up with next.

Stick around a few years and it could get interesting for sure.

I digress
;0)
Robyn

[450]

Actual broke crank and related carnage...1983 vintage, 190,000 or 290,000 miles, good balancer (before and after)..freeway driving, no trailer this time, in 3/4 sub, gradual incline, started LOUD hammering for several seconds before it exploded and stopped, coasted to a park and ride. No previous warnings or indications of impending damage...kinda scary when you think about it, not working it hard, just cruising the e-way at 70 mph or so..with overdrive, oil pressure and temps good. Tear down revealed the broken crank and the webs ripped out almost to the cam. My opinion in my case was the crank went first andd ripped its guts out.

[Robyn]

I agree
I think the cranks on some are a piece of taffy and tweek and flex until they let go.

I have no way to prove this but my gut instict says this is the culprit.

Never had one of mine break but there is always the first time.

[gmctd]

We see cranks break at the nose - would seem to indicate HB imbalance

We see cranks break at the output end - seemingly indicates output imbalance

Some of those never damaged the blocks

We see three-piece cranks, invariably with crumbled mains, seemingly indicating the block cratered, took out the crank

IIRC, JK's first attempt at hi-perf, the crank immediately took up residence in the oil pan, along with the three center mains-webbing - he reused that crank in his next edition.

We see blocks with no indication of crank trouble - pull the pans for inspection to find varicose vein cracks or cracks in the main-cap outer bolt-holes

We've seen what looks like a rod thru the crankcase, only to find that it's both rods, still on their crankpin, multi-piece crank, mains-webbing gone

Bone-yards can be very interesting places - but, what can you say?

Appears to me the block is a bigger problem than the crank, which is a big problem.

'Course, I'm talking 6.5's here, but the 6.2's don't run as hot, because they don't have 6.5 power - yet they suffer the same fate