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Discussion Starter · #1 · (Edited)
Visited the GM Powertrain/GM Media Online site today and downloaded .doc, .xls and .jpg files in connection with the 3.6L DI LLT engine for the CTS for M-Y 2009 and M-Y 2010.
Links to pages visted:
2009 GM Powertrain info: http://archives.media.gm.com/us/powertrain/en/product_services/2009/09car.htm
2010 GM Powertrain info: http://archives.media.gm.com/us/powertrain/en/product_services/2010/gmna/10car_us.htm

Nothing is mentioned in the .doc or .xls files for the 2010 3.6L DI engine as far as any revisions or design changes made for 2010 (compared to the '09 engine), but it's clear from the .jpg images (2009 LLT vs 2010 LLT) that GM revised some of the front end of the LLT engine for 2010+.
Photos of both M-Y engines are included below. Notice the changes in belt routing (i.e. a single belt for 2010+ vs. the former dual belt configuration) and the reduction in the number of belt tensioning components/pulleys (i.e. 1 tensioner only for 2010 vs. 2 tensioners and 1 pulley/belt router component for the former 2008/09 config.) :

2008/09 GM 3.6L V-6 VVT DI (LLT):


2010 GM 3.6L V-6 VVT DI (LLT):


So.. do the 2010 changes represent functionality/reliability improvement(s) or do they relate more to cost cutting? Perhaps of greater importance are potential changes in components we can't see in the image.. such as the timing chain(s).
Is the timing chain an issue only on the '08/'09 CTS? Is the timing chain issue (described as 'chain stretch' in several posts here) a chain supplier quality issue, or is it more related to engine design? If it's an engine design issue, was it fixed with the 2010 engine revision(s)? All interesting points to consider.
 

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i thought the chain issue was with the older engines LY7(?) mostly in like 2006 year model, for instance

but more to your question: i would assume that most of what you're seeing different is a combo of what you've guessed (reliability & cost)
they've gone from two to one belt (most major change i can see from the pictures) this is probably mostly a cost issue, less parts
slightly different a/c compressor (see the hose port connections) probably a design change for reliability, but maybe cost too
coolant outlet has been moved (drivers side center to passenger side center) i'm not sure about this one
oil filter housing heat shield slightly changed (that head shield is covering the base of teh filter housing and maybe something else, but it looks just slightly changed)

slight changes are usually about reliability (engineering) but since making a slight change may or might also be cheaper it's really hard to tell
costs come down with fewer parts (see 2 belts and tensioners -> 1 belt and tensioner)
costs also come down when you don't re-engineer stuff so it's really hard to tell

overall i would think that they're probably just about the same internally, but there's been some slight external/accessory changes here
i would expect this design to last at least three years as the original LLT, but the longer they let it stay the more ROI they get on their engineering
but you know they're always engineering so, maybe the engineering costs are fixed year-to-year

ok i'm done... hope that sheds some light for you
 

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Discussion Starter · #3 · (Edited)
Chris, thank you for your insight/comments.

My gut feeling is (was) that the 2010 changes were mostly about cost cutting, when looking at the identifiable changes in the photos.

The biggest driver for me today was my renewed concern about the timing chain on the '08/'09 CTS LLT engine. There are threads here in this 2008+ CTS forum about it. When I performed a search today in the forum for "timing chain" I found those threads... and it appears all chain failures & issues so far have been on '08 & '09 CTS's (which makes sense, since most '08 & '09 CTS's will have generally accumulated more miles than a given 2010).
There was one post I read where the forum member advised he was having to get another (his 2nd) timing chain installed at 24,000 miles after having had the 1st replacement timing chain installed around the 12,000 mile mark. Not good!! The requirement of a 2nd replacement timing chain suggests there could be something else going on besides the original 'chain supplier quality issue' story that was released/circulated.
Another poster said his '09 CTS (built in April '09) required a new timing chain. My '09 CTS was built in May '09! :suspense:

I suppose my concern for today is... I love my fully equipped 2009 CTS, and I could easily keep it for many years... I'm presently not putting many miles on it (the odometer is currently at 11,000 KMs / 6,800 miles).. but I wouldn't want to be keeping the car for say 6 years (2 years beyond the expiration of full-vehicle warranty) if there's a good chance the timing chain could fail catastrophically in year 5 or 6. If GM have done something very specific about the timing chain issue beginning with the 2010+ CTS LLT engine.. well, I'd like to know about that now rather than later.

Chris.. can you check on whether there's been any part number changes for the timing chain(s) on the 2010 CTS LLT engine vs. the 2008/09 CTS LLT engine? A part number change could indicate a component revision or some level of redesign.
Also... do you know if there might be a TSB that's been issued that could assist with the identification of a timing chain that's on the road to failure on a 2008+ CTS? In other words.. does the owner (and the dealer service dept.) have to wait until the 'Check Engine' light comes on before taking any action in this regard?

Thanks,

Richard
 

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So the guys in the shop seem to agree with the forum that low oil level is the main cause of the timing chain problems.
They said that first you get some noise and then you'll get the check engine light - by that time you need replacement.
If you don't do anything about it you'll eventually have catastrophic failure.
They said that a small percentage just have the chain break with no warning, but most will give you a heads up.
So making sure your oil level doesn't drop too far is about the only thing you can do to keep having the chain problems.

as for the chain part numbers themselves there has been no update to the chains
the same chains are used on the 2.8L 3.0L and both 3.6L engines

this made me think and go back to the original cause of the chain problems being oil level

i guess the main thing that we would like to see in the updated engine is a stop to the mysterious low oil problems
 

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Discussion Starter · #6 · (Edited)
Chris - thanks for coming back with your additional comment/information.

BTW... a friend of mine who lives in Missouri [he's a retired GM engineer who drives a 2008 3.6L DI CTS and who used to post in this 2008+ CTS forum]... recently had an event on his CTS where the 'Check Engine' light came on. He brought his car into the dealership and after some diagnosis they advised that the engine timing chain(s) had to be replaced. There was NEVER a low engine oil situation with his CTS (he ordered & bought the car new, in summer 2007). He is meticulous about maintenance and care for his cars ('08 CTS and '10 Corvette Grand Sport Convertible)... the sort of individual who checks engine oil level at every gasoline fill-up. Because of what's happened with his CTS (timing chain change-out required at an early stage), I have some difficulty at this point accepting low engine oil level as being the primary cause of the chain problems. I believe there's more to this story than what's being said / being reported at the dealer level.
A broad explanation by GM / dealerships as 'low engine oil level' being the primary cause of timing chain failure (with very possible catastrophic engine damage) essentially places partial or perhaps full blame for a catastrophic event on the owner/operator of the vehicle, rather than the manufacturer of the engine (GM).

For illustration purposes... below is a cutaway view of the 2008/09 3.6L V6 DI LLT engine. Some detail of the timing chains can be seen in this image.



--------------------------------------------------------------------------------------------

Text added below copied from a page at CaddyInfo.com
Link to webpage: http://drupal.caddyinfo.com/?q=node/44

Cadillac DI 3.6L (LLT) engine details, 2008
10/06/2007

. . . . "The 3.6L V6 VVT DI has a new timing chain with a smaller pitch (7.7 mm compared to 9.5mm previously) and more links. The chain features an inverted tooth design. The smaller links engage at a lower impact speed, which decreases the noise generated. In conjunction with the new chain, the number of teeth on the sprockets is also increased, increasing the meshing frequency and further reducing noise and vibration.
The new timing chain is a running change that will occur in all of GM Powertain’s V6 VVT engines through the course of the 2007 model year".


---------------------------------------------------------------------------------------------
 

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I wonder if the timing chains are also a problem with this engine and it's derivatives used in other vehicles such as the Saturn and Chevrolets.
 

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I talked to some more of the techs who have done the timing chain work for us and they seemed to agree with what you're thinking RAB - there really is no explanation (at least at the dealer level) for what's happening to these chains besides they're "just wearing out"

now maybe something else besides the chain material and construction is causing the premature failures but whatever it is I'm sure that's a top secret at GM

and yes C "T" ess, the other brands do use this same chain design in their engines (many of which are the exact same - LY7) and this is not just a cadillac problem but a gm problem since the engine is shared across the brands
 

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I know wikipedia is not the be all, end all on info, but reading THIS brought up some questions.

The guys with multiple chain failures, do they need the sprockets replaced as well?

Could it be possible the problem is in the sprockets themselves, and not the chain? In other words, are the sprockets wearing out the chain?

If oil is a problem, is it with low engine oil caused by lack of maintenance, or is it a design flaw internal to the engine? Did the larger chains hide this problem?

Please beat me if these are ignorant questions!
 

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i'm going to ask some questions this week at work and see if i can get a answer in reguards to the timing chain failures
 

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I wonder if the timing chain issue is connected to the camshaft play issue that there is a TSB on. I'm sure that if there's play in the cams that it could cause excess stress on the chains. I wonder how many chains are replaced without them looking into the camshaft issue, and on the flip side how many cam issues are fixed without replacing what could be potentially damaged chains.

For what it's worth I have an '08 built in September '07 with 62,000 miles on it that's never had either issue. Hopefully I didn't just jinx myself...
 

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Discussion Starter · #13 · (Edited)
I know wikipedia is not the be all, end all on info, but reading THIS brought up some questions. The guys with multiple chain failures, do they need the sprockets replaced as well? Could it be possible the problem is in the sprockets themselves, and not the chain? In other words, are the sprockets wearing out the chain? If oil is a problem, is it with low engine oil caused by lack of maintenance, or is it a design flaw internal to the engine? Did the larger chains hide this problem? Please beat me if these are ignorant questions!
No need to beat you brothleutner, as they are all good questions! :thumbsup:

When you read their tech & media documentation.. it's clear that GM intends for their LLT engine (along with all other engines they offer) to operate 100,000 miles before servicing / engine component change-out is required, whether you're talking about spark plugs or accessory drive belts or any other engine component you can think of (with the exception of filter elements of course).

Per GM's dissertation(s)... "The cam drive and valvetrain components require no scheduled maintenance. A sophisticated cam-chain tensioner, high-quality cam phasing components and hydraulic lash adjusters are designed to ensure optimal valvetrain performance for the life of the engine with no adjustment".

One assumes the mention of "valvetrain components" also includes timing chains. So given that.. timing/cam chains should last the life of the engine. Okay. So what is the expected/anticipated life of an engine these days? 200,000 miles? 300,000 miles?

For a timing/cam chain(s) to break or require replacement at a stage before the life of the engine is realized is a fail. For the chain(s) to break or stretch or fail for whatever reason before 100,000 miles are earned on the engine is a MAJOR FAIL. For it to happen before 50,000 miles or incredibly 25,000 miles.. well that is VERY VERY significant and absolutely NOT GOOD at all.

I suspect the number of timing chain events so far on the 2008+ LLT engine is significant, but not, as yet, a huge problem for GM as these sorts of things go. GM are doing well at containing the problem/failures, as dealer service depts don't seem to know what the true story is. It's certain that at GM Tech & GM HQ levels.. engine teardown analyses have been performed and primary cause has likely been more or less identified. GM has to know all this stuff but obviously they're not telling.
It could be a random thing.. like a fluke stack-up of manufacturing tolerances (something like 5 or 10 engines in a thousand)... or an inconsistency in the manufacturing quality of the chains or chain tensioners.. or some inconsistency in how well the chains are lubricated within the engine.

To me, it appears the timing/cam chains are the achilles heel of the 2008+ CTS 3.6L DI LLT engine. Maybe we'll find out one day what's really going on here.
 

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Slightly off topic (but not really to the original question), but the engine's fuel economy did go up 1 mpg for 2010. Perhaps the redesign was for less drag in the accessories to eek out a little more fuel economy. That may have been the whole point of the redesign or just an added benefit.
 

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Discussion Starter · #16 · (Edited)
Slightly off topic (but not really to the original question), but the engine's fuel economy did go up 1 mpg for 2010. Perhaps the redesign was for less drag in the accessories to eek out a little more fuel economy. That may have been the whole point of the redesign or just an added benefit.
smithb, that's an interesting take on the 2010 LLT engine redesign. That's really thinking outside the box.
So... whatever the order of importance for the engine redesign.. >: reduced accessory component count.. reduced production cost.. reduced accessory/front end complexity.. lower parasitic load front end arrangement.. potential reliability improvement (based on reduced component count).. better fuel economy (according to 2010 fuel economy numbers). This appears to be a significant "win" in every category, and kudos for the LLT engine re-designers.
However I'm still concerned about the timing/cam chain issue(s) with the LLT engine. (Was it addressed with the 2010 engine redesign?).
Meanwhile.. there's my very nice '09 CTS that could have timing chain issue(s) sometime down the track.
 

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fwiw, the re-designers are probably the original designers... but you never know

i guess we'll have to wait for the 2010's to get some miles on them to find out if they've got timing chain problems
since gm isn't going to come out and say 'we fixed the timing chain probleme too!' because that would be an admission that the problem existed

from what i can tell GM figures that all the ones that fail before 100K will be taken care of under warranty and if they make it that far without failure then the chances of failure are much much greater that it won't happen after the 100K and the % that fail after the warranty will be too small to care about (from their standpoint)

this is all reminiscent of the N* head gasket issues to me

and another thought: i'll check the chain tensioner part numbers tomorrow and see if they've got new numbers as that could be the main problem too i guess
 

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today i got some info on the timing chains....the reason they were stretching is a supplier problem with the timing chain being too soft ....resulting in timing and cam phaser codes . not sure when the break point is on the new improved chains ....i'll look into that,,i'm guessing it was around the spring of 2009 . i'll try to get a more specifice date
 

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Correct me if I'm wrong, but normally when a roller chain stretches, it's not the links actually getting longer, but the rollers between coming loose. This is caused usually by dirt or lack of lubrication, so I'm not dismissing it's a chain problem, but I'm not ruling out something else either.
 

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i can't really comment on the dirt or lubrication theroy....i got my info from a engineer that works on the
V6 engine line
 
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