Not sure if this has been discussed already, but I couldn't find it in my search. I scratch my head and wonder why the 05-06 CRD's have a timing belt when the same model year gas versions are using timing chains. Are diesel engines just not able to use that type of setup?

Totally different engines, totally different designs. Different execution.

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A parent's reply would be "because" which translates to no particularly good reason.

Mechanical timing between crank and valves, as opposed to ignition or firing timing, is obviously controlled by mechanical means. Back in the day most all engines used timing chains riding on steel toothed gears, which were superseded by timing chains riding on plastic toothed steel gears, which were superseded by timing belts ostensibly because those shifts produced progressively quieter engines. Having driven and worked on all 3 types I don't believe for one second the "quieter" argument rather I believe cheaper to make and maybe planned obsolescence. Chain on steel gears could last somewhat over 100,000 miles when lubed properly and probably longer if a tensioner was in the system. Chain on plastic toothed steel gears might make 100,000 miles before the teeth were gone. Early timing belts were lucky to make 75,000 miles and almost never made 80,000 miles. I've omitted direct gear to gear driven timing as I understand that's relatively uncommon.

If I was guessing timing belt driven systems are more common where the design of the engine is such that the belt does thing other than just keep crank and valves in time. For example the CRD TB drives the CP3 and the water pump in addition to the 2 cams.

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Sold to LOST member my 05 Ltd, GDE Stg II turbo + TCM tune, SunCoast TC w. Transgo kit, Steiger window regulators, Samcos, Fumoto valve, 2nd gen filter head with Lub. Spec. bleeder, Hayden clutch & 11 blade fan, inverted spare, P-1 battery, BF Goodrich Long Trail TAs, Etecno1 glow plugs, timing belt at 50K miles/8 yrs

@ papaindigo

Gear to gear timing is fairly uncommon except on heavier diesel engines. My 1985 Ford F250 with the 6.9L uses gears to time the crank, camshaft, and injection pump. That setup will run forever with out issues, i believe the 5.9L Cummins is that way as well.

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05 CRD Sport - GDE EcoTune - Samcos - EGR Delete & Elbow kit - ARP Studs - Airtex E7181M

Interesting re. the Cummins which I had not realized was gear driven direct mechanical timing.

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Sold to LOST member my 05 Ltd, GDE Stg II turbo + TCM tune, SunCoast TC w. Transgo kit, Steiger window regulators, Samcos, Fumoto valve, 2nd gen filter head with Lub. Spec. bleeder, Hayden clutch & 11 blade fan, inverted spare, P-1 battery, BF Goodrich Long Trail TAs, Etecno1 glow plugs, timing belt at 50K miles/8 yrs

The older VM engines (with IDI and individual cylinder heads) used a geared system...circa pre 94 through 98. The belt drive in diesel was a short lived experiment for the most part. Timing chains can last 250k+ on new diesels and still very quiet. The mercedes 3.0l diesel has a timing chain with over 300-400k miles on stock system in some Sprinter vans.

Gear drive is needed for maximum system robustness for million mile engines like Cat, Series 60, Cummins, etc. A cast iron head is also on these engines.

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The whole purpose for belt driven camshafts (instead of chain or gears) is to suppress vibration.
Belt drives work great. They just dont last very long.
In fact, they work so great that they are used in racing engines, completely out in the open , with no cover.
And they are promptly replaced after every race.

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