VORTEC 8100

[canuck]

A friend of mine has a 2001 GMC Sierra 2500HD with the Vortec 8100 engine and Allison transmission. He currently has 30,000 + km (about 19,000 miles) on it and is quite pleased with his truck.

 

However, it is at the shop right now, with a cracked cylinder head. The crack is apparently near an exhaust valve.

 

He hopes that this incident is caused by an assembly problem during manufacture, rather than a problem that is symptomatic to the 8.1 litre engine.

 

I somehow doubt the assembly problem theory, since I think such a problem with a cracked cylinder head would manifest itself within the first few thousand miles, rather than at 19,000.

 

Does anybody have any comments and or suggestions? We would much appreciate it. Thanks.

[Shaners]

I haven't heard of any cracked heads on any of the Vortec motors.  I feel bad for your buddy, but I would say it is an isolated incident...

[awdvkd]

Bad casting, maybe!-Did it overheat!

[canuck]

awdvkd,

 

no overheating problems.  Also, he is a very careful driver and does not abuse his truck.

[CMNTMXR81]

It's a fluke.  Mine is the only 8.1 that has come into the service lanes at our dealer and that's only cause I bring it in to use the hoists.  Heck, more D-Max's have come through.

[canuck]

Shaners and CMNTMXR81,

 

Thanks for the input, that will help to calm my buddy somewhat.  He is concerned and so is his wife, since this is the second time they had problems with the Vortech 8100 / Allison combination.  The first time was right at the beginning: he was driving off the lot with his new truck (he just traded his 6.0 L Sierra in) and he noticed a really bad engagement of the Allison.  The tranny was replaced shortly thereafter.

 

So, naturally him and his wife a very concerned about the whole powertrain!

 

I believe the tranny problem was a fluke and something went wrong during the assembly.  The Allison is certainly a good tranny.

 

However, the cracked head after 19,000 miles has me puzzled.  I would expect the thing to go much earlier, IF it was an assembly problem, such as a faulty casting or a miss-torqued bolt.  That it took so long, kind of worries me (and him).

 

Thanks for the advice.

 

BTW, I am driving a 2002 F-350, PSD, 4x4, SRW.  Will you guys still talk to me now?

[CMNTMXR81]

Yea, we'll still talk to you but we'll just ridicule you.  

 

Anyway, mine just turned 15,000 miles, and I am VERY hard on mine.  I think nothing of tampering with it and mine has held up to the abuse.  Big Block GM engines in general are very durable engines if not some of the most durable.  Keep in mind, this iteration of the BBC (Big Block Chevy) is only a year old, so you gotta give them time to work out the kinks.

 

As to Allison problems, fried Allison #3 in some 1.5 - 2 years of selling them came back last Thursday.  So I wouldn't worry too much about that either.  They do have minor issues with programming though.  But that's easily fixed.

[canuck]

CMNTMXR81,

 

Wow, world peace must be making progress – a GM guy talking to a Ford guy. *grin*

 

Could you tell me if the exhaust valve seats in the heads of these engines are just hardened or if a seat is pressed in after they cast the head?

 

I can imagine a hairline crack developing during this process and then just taking its time to work through.  The 8100 is certainly a bull of an engine and the internal working pressures and heat build-up must be quite high for a “consumer oriented” gasoline engine.

 

Thanks for the help

[CMNTMXR81]

Yea, well with all these ricers inhabiting our land, we domestic guys have mended our fences and allied our forces.  

 

As to the valve seats, only the exhaust valve I believe has a seat insert.  Which bingo, would explain why it happened near your friends exhaust valve.

[canuck]

CMNTMXR81,

 

Of course, us guys have to stick together.  Nothing beats Detroit iron, and I mean nothing.

 

Let’s hope the exhaust valve seat was the problem, causing the crack.  The problem started (I think), at about 14,000 miles, when my friend complained about coolant loss.  Naturally, he kept the coolant topped up and he went to the dealership, where they pressurized the system.  They could not find any problems.  Eventually, it got worse and a valve started knocking, hence they tore the engine down.  Diagnosis: cracked head.

 

You seem like an ok guy and I kinda like the specs of your truck.  HOWEVER, it might be time for you to learn something:  REAL TRUCKS do not have sparkplugs!  *grin*

 

With a diesel, you can scare the daylights out of old ladies, small children, cats and, most importantly, any rice burner *huge grin*

 

Thanks for the advice

[Growler]

I have to agree with canuck that nothing beats Detroit iron (well, Pittsburgh STEEL anyway).  Aluminum, on the other hand, is a different animal.

 

Steel has a neat property known as an ENDURANCE LIMIT.  Basically, it is a stress threshhold below which pre-existing flaws (cracks) won't grow no mater how many stress cycles they endure. Aluminum doesn't have that. What that means is that, given enough stress cycles, anything made of aluminum will eventually fail due to fatigue.  So the basic design philosophy with aluminum is to determine how many cycles of a given stress magnitude you need something to last for, use that and the stress level to determine a maximum allowable flaw size, and then try to make sure that all of the pre-existing flaws in your material are smaller than that.

 

I believe that the heads on an 8.1L are made of aluminum (with steel inserts), and it isn't hard to imagine that one occasionally gets made with a large enough (but still tiny)undetected flaw that the fatigue life is far less than one would like.  Sounds like that is what may have happened to your buddy.

[02 2500 Avalanche]

The heads on the 8.1 are cast iron not aluminum, I wish they were aluminum though, it would save some weight on an engine that could be used as an ancor on a cruise ship  

 

Alex

[RyanbabZ71]

Steel has a neat property known as an ENDURANCE LIMIT.  Basically, it is a stress threshhold below which pre-existing flaws (cracks) won't grow no mater how many stress cycles they endure. Aluminum doesn't have that. What that means is that, given enough stress cycles, anything made of aluminum will eventually fail due to fatigue.  So the basic design philosophy with aluminum is to determine how many cycles of a given stress magnitude you need something to last for, use that and the stress level to determine a maximum allowable flaw size, and then try to make sure that all of the pre-existing flaws in your material are smaller than that.

 

Wow sounds like my senior design project.  Fatigue properties of D2 tool steel (heat treated vs cryogenically treated)

[SoMnDMAX]

CMNT, are you sure the 8.1's exhaust seats are inserts? Doesn't sound right... Especially in an iron head. 99.99% of production iron cylinder heads I've seen have had induction hardened seats.

 

Canuck, I would bet your buddy got a bad casting. Iron castings can hold inclusions that won't show up until after the parts are in service for a while, typically resulting in a crack or void. These inclusions may include- hard spots, foreign material, porosity, or a cold pour. The head could have been cracked from the start. I see  a bad casting or two every week where I work. Out of every thousand pours, there is bound to be a bad casting that will slip past quality control.  S*** happens.  

[SoMnDMAX]

Wow sounds like my senior design project.  Fatigue properties of D2 tool steel (heat treated vs cryogenically treated)

Icky...

 

Have fun!!