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I found this discussion and video about the inline 6 cylinder 3.0 liter Duramax diesel. Scroll through the discussion and locate the video.

2020 Chevrolet Silverado Duramax Turbo Diesel – A Record Setting 33 mpg Highway Rating! (at http://www.cleanmpg.com/community/index.php?threads/56410/ )

It is just amazing some of the designs that engineers put forth. On this engine the overhead cam is driven by a chain drive system from the rear of the engine. You drop the transmission and remove the flywheel to gain access. The engine oil pump is BELT driven from the rear of the crankshaft. At time interval 3:10 the presenter indicates that if the belt fails, an appropriate diagnostic message will appear and you will have ample time to stop the engine due to lack of oil pressure.

This is about as insane as the VM Motori designing the 3.0 liter ecodiesel V6 engine with camshaft sprockets NOT KEYED to the camshaft. Sprockets are just a friction fit and expected not to slip, get out of time and trash the valves against the pistons.
 

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Keyed sprockets wouldnt have helped a bit, they are just like dowel pins only there for indexing reasons.
- its still the friction that does the holding work.
Dont lump that feature togheter with strange design decisions that can be ridiciusly difficult to maintain.
 
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The cam shafts in the early 3.5 Liter V6 are also not keyed.
But it has a very long bolt that threads into the cam shaft. And looks like the cam shaft it held in compression holding the sprocket on?
 

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What is the lifespan of the chain drive for the Duramax? If it's 300,000 miles, that level of expense for replacement is acceptable.
How hard is it to replace the oil pump belt? (I'd imagine that's very hard). At that point, I wonder if an electric pump is possible!
 

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. . . . .What is the lifespan of the chain drive for the Duramax? If it's 300,000 miles, that level of expense for replacement is acceptable. . . .
Any chain drive will wear and stretch; some designs more than others. GM has had some short lived camshaft chain drives (less than 100,000 miles) in vehicles over the years. It seems that the GM 3.6 liter V6 is notorious for cam chain problems. At least that is on the front of the engine and you don't need to drop the transmission. If the design with cam chain drive at the rear will last 300,000 miles or more then it is less of an issue. But having to drop a transmission to access a camshaft chain, question that wisdom. Placing the cam drive chain at the rear does not save space versus having it mounted on the front of the engine.

. How hard is it to replace the oil pump belt? (I'd imagine that's very hard). At that point, I wonder if an electric pump is possible! . . .
From comments in the video the engine and transmission would have to be separated and the oil pan dropped. If you used a chain you could remove a connecting link and remove the old and install a new chain without separating the transmission from the engine.

One could wonder why have a separate oil pump with a belt or chain drive. Why not make it concentric with the crankshaft which is still used on many engines?

Considering all the electric gizmos on modern vehicles and the attendant failure rate, having a solid, reliable mechanical drive to a vital component such as engine oil pump would be better for longevity.
 

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Any chain drive will wear and stretch; some designs more than others. GM has had some short lived camshaft chain drives (less than 100,000 miles) in vehicles over the years. It seems that the GM 3.6 liter V6 is notorious for cam chain problems. At least that is on the front of the engine and you don't need to drop the transmission. If the design with cam chain drive at the rear will last 300,000 miles or more then it is less of an issue. But having to drop a transmission to access a camshaft chain, question that wisdom. Placing the cam drive chain at the rear does not save space versus having it mounted on the front of the engine.



From comments in the video the engine and transmission would have to be separated and the oil pan dropped. If you used a chain you could remove a connecting link and remove the old and install a new chain without separating the transmission from the engine.

One could wonder why have a separate oil pump with a belt or chain drive. Why not make it concentric with the crankshaft which is still used on many engines?

Considering all the electric gizmos on modern vehicles and the attendant failure rate, having a solid, reliable mechanical drive to a vital component such as engine oil pump would be better for longevity.

Why not use gears instead of a chain like the big inline sixes?
 

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Gears - I would guess cost and space.
Really, WRT the chain, it all depends on the chain durability; there are amazing advances in durability every year.
For the oil pump belt, though... if you have to separate the engine and transmission... it sounds like the old Fiero V6 syndrome. “Yes, we did tell you to remove the engine for every spark plug change.” (Though clever mechanics took the fenders off instead.)
I was annoyed with my Camaro that I had to remove the wheels to change spark plugs, but apparently some Mopars had the same process - at least with seriously large engines; the Camaro was just a 305.
 

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I was annoyed with my Camaro that I had to remove the wheels to change spark plugs
Had to do the same with the '94 Aerostar 3.0L V6 we had. What a pain.

Don't forget the Monza/Sunbird models with the 265 cu in V8 - there was one spark plug where the engine had to be lifted to replace it. Many dealerships would change the other 7, never bother with the inacessible one and charge you for changing 8 (at least, that's what I heard).
 

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Things such as chains on the rear of the engine and friction fit cam and crank sprockets arent new.

In fact, GM is quite late to the game implementing this stuff.
 

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First, having owned a tune up shop, you would be surprised at the number of Mopar B and RB engines I saw that #7 spark plug still had the paint from the assembly line on the Mopar plug.

Chain drives, let us revisit the Mitsubishi 2.6L engines where the oil pump/balance shaft chain would eat the guides then trash the whole thing.

Mercedes - Benz engines look impossible to do the chains on, but, with the followers off the cams and plugs out, one turning the engine by hand while the other handles old out - new in until the connecting link appears even the V8s aren't bad. Porsche 911 engines (flat 6) have the chains on the front of the rear mounted engine, engine must be removed to replace them and apparently the tensioners are short lived, Ford OHC 4.0L V6, even better, 3 chains, one where the normal pushrod cam drive would that ran a jackshaft for the two upper chains (one in front one in back) and the oil pump gear driven by a dummy distributor drive at the back of the engine.
 
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Chain drives, let us revisit the Mitsubishi 2.6L engines where the oil pump/balance shaft chain would eat the guides then trash the whole thing.
That must not have been the norm, though, the 2.6 had a pretty good rep other than the carb.
 

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That must not have been the norm, though, the 2.6 had a pretty good rep other than the carb.
Actually this was a fairly common issue with them. My friend worked for a Chrysler/Plymouth dealer in the early 90's and they repaired quite a few of 2.6 engines once the chains had a problem. Between that and the valve seals on the 3.0, the mechanics there really hated the Mitsubishi powered minivans.
 

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Exact thing happened to my friend '85 Caravan 2.6. Guides went, chain got loose and took out the engine. that was its second set. (first was replaced in the early 90's. They knew it was getting loose but it was 2001 and the van was just on borrowed time anyways. one day it let go and that was it. Plus the carb was getting very temperamental. Now its only one but interesting to hear more people had the same issue.
 

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It's odd that it was so common, and yet so many people hit 200,000 miles with the 2.6... the carb was trouble. The 3.0 valve seals were similar - they did go but the rest of the engine seemed very durable and there were lots of high-miles ones. So did people jsut fix the 2.6 chains and keep going?
 

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If you caught them before something broke you were ok, problem was the balance shaft chain was also the oil pump drive chain and it was a single row chain that had to turn the balance shafts at twice crank rpm. If you were at speed on a freeway or other limited access high speed road, the engine might be turning 3K, but the oil pump and balance shafts were turning 6K.
 

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First, having owned a tune up shop, you would be surprised at the number of Mopar B and RB engines I saw that #7 spark plug still had the paint from the assembly line on the Mopar plug.

Chain drives, let us revisit the Mitsubishi 2.6L engines where the oil pump/balance shaft chain would eat the guides then trash the whole thing.

Mercedes - Benz engines look impossible to do the chains on, but, with the followers off the cams and plugs out, one turning the engine by hand while the other handles old out - new in until the connecting link appears even the V8s aren't bad. Porsche 911 engines (flat 6) have the chains on the front of the rear mounted engine, engine must be removed to replace them and apparently the tensioners are short lived, Ford OHC 4.0L V6, even better, 3 chains, one where the normal pushrod cam drive would that ran a jackshaft for the two upper chains (one in front one in back) and the oil pump gear driven by a dummy distributor drive at the back of the engine.
Lol that absurd Ford design is what led me to buying my '98 Jeep Grand Cherokee with the eons simpler (and much better) AMC/Chrysler/Jeep six.
 

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Good point, but, I don't want nor does my wife an SUV of any kind. she does not like climbing up into things (like my truck). She and I both had a string of Mopar minivans, 1989, 1993, 1997, 2003 and 2005. The 2005 was traded in on the 2011 Ford Flex.
 
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