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Thread: Gear Drive vs Chain Timing Sets

  1. #1
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    Arrow Gear Drive vs Chain Timing Sets

    Reprint from an article produced here in The Diesel Page in 2003
    Chains or Gears?
    Which is Best?
    6.5 Timing Set Pros & Cons


    What are the advantages and disadvantages of using a gear-drive timing set? Let's consider this question, and have a look at some of the related issues involving the 6.2/6.5 gear and chain timing sets.

    Three rumors we've heard about the gear-drive timing sets:

    #1 "Gear-drives contribute to broken crankshafts."

    Reality: A defective elastomer in a harmonic damper or torsional dampening crank pulley can result in a broken crankshaft. A broken cylinder block can result in a broken crankshaft. A defective flywheel or flexplate can result in a broken crankshaft. Knowledgeable mechanical engineers all agree that the purpose of the crankshaft mounted harmonic damper is to reduce harmful torsional vibrations that can and will fracture crankshafts if not controlled.

    (Added 6/1/09) Our own 6.5TD Power Project engine ran normally with a DSG gear drive timing set for more than 250,000 miles before it was sold in 2006. I believe weak cylinder blocks and/or defective dampers, pulleys or flywheels are the cause of broken crankshafts. Whether or not an individual vendor recommends a gear drive for the 6.5 depends on whether they sell it. It's that simple. The Diesel Page doesn't sell the gear drive nor does it sell any other part for your truck. The best and most reliable information is what we're interested in.

    #2 "The front end of the idler gear axle shafts rub destructively on the aluminum timing cover."

    Reality: When a gear drive timing set has been installed correctly, 6.2/6.5 engines that have been disassembled after running hundreds of thousands of miles all show that axle shaft rubbing on the aluminum front cover is of no concern.

    #3 "Gear-drive timing sets are noisy."

    Reality: My hearing might not be what it used to be, but after listening to at least a couple dozen 6.2/6.5 engines that were equipped with a DSG gear-drive, I have yet to detect any gear noise. The timing and camshaft advance produced by a gear-drive usually result in a more crisp combustion rattle. This should not be confused with gear noise. Whether or not one can detect any gear noise, it is just a small and insignificant contribution to the overall noise level produced by a running 6.2/6.5 diesel engine. You can hear the gear drive if you remove the oil filler cap on a running engine. I can't hear it otherwise.


    The factory original 6.5 timing chain set shown above produced about 5/8" (.625") of chain slack. The GM maintenance manuals specify a maximum of .800", while most new chains produce about .250" to .500" of chain slack. GM specifies .500" of chain slack as the maximum acceptable limit for a brand new chain. Obviously, there is a lot of variability.

    The 5/8" of chain slack shown in this photo produced about 3 degrees of crankshaft rotation before the gear bolted to the injection pump would begin to move (this equals approximately 3 crankshaft degrees of slop in the timing set). A chain with approximately .250" of slack produces about 2 degrees of crankshaft rotation, and a worn-out chain with .800" of slack will produce 4 degrees or more.

    The various timing gear sets I've installed have all produced approximately 2 degrees or less of crankshaft rotation, which in contrast to a chain, will change very little throughout the life of the engine. The primary advantages of a gear-drive timing set are: lower mass, built-in cam and injection pump advance (power & fuel economy improvements), more accurate fuel injection timing for the life of the engine with little to no change over time and miles (unlike a timing chain).


    Member Scott Boelman made the following report after installing a DSG Phazer gear-drive timing set:
    • "I carefully calculated my fuel economy during the 1588 miles prior to installing the Phazer kit. During this time, my truck averaged 16.9 mpg. In the 1758 miles since the installation, my fuel economy has improved to an average of 17.4 mpg. This is a 3% improvement in fuel economy. Driving conditions were similar for both test periods, primarily highway driving at 70 to 75 mph.


    • Power runs using full throttle can provide a good measure of engine power changes. However, acceleration testing a manual transmission equipped truck presents a slight problem in reproducibility. Minor changes in technique from one run to the next could produce big changes in elapsed time. To minimize driver error I ran the acceleration tests in 5th gear from an indicated 45 mph to 75 mph (similar to a passing acceleration test). Prior to the installation, a series of 45-75 mph 5th gear acceleration runs produced an average of 17.41 seconds. Following the Phazer installation, the average elapsed time was reduced to 16.96 seconds. This is an improvement of 0.45 seconds and translates into a 2.7 percent faster time."


    The 1982-84 6.2L diesel engines were equipped with stamped steel V-belt crank pulleys. GM introduced a torsional dampening crank pulley in the 1985 model-year in an effort to improve belt life and improve belt-driven accessory life. Anyone who has tried to keep V-belts on the 1982-84 6.2L engines know that unless kept exceedingly tight, wild gyrations are seen in the belts at idle or low engine speeds. Belt resonance is due to cylinder power impulses, which causes the crankshaft to slow down during each compression stroke, then accelerate on each power stroke.

    The same sort of harmonic resonance can occur with a loose timing chain. Resonating timing chains can cause all sorts of trouble. Aside from making it more difficult to accurately set the injection timing, loose timing chains can also result in sheared DS4 drive-head shear pins and loosened camshaft bolts - all due to high momentary torque loads caused by loose and resonating timing chains.



    The above image shows a mainshaft that had been removed from a DS4 electronic fuel injection pump. This pump (that the shaft was in) was pulled from service because the drive-head (pinned and bolted to the forward end of the shaft) had sheared the pin, and had begun rotating independently of the DS4 shaft. Obviously, the engine can't run when this happens. Aside from this shaft, I witnessed another occurrence of this problem at our local Chevy dealership a few years ago. The drive-head on that DS4 had sheared the pin and was somewhat loose on the pump shaft.

    Beginning about 1996, GM upgraded the cam bolt to a grade-10, and nearly doubled the camshaft bolt torque from 65 ft/lbs to 125 ft/lbs. A thread locking sealant is also now specified for the cam bolt, to help prevent it from loosening.

    The questions that beg an answer is why did these DS4 drive-head pins shear, and why did GM increase the camshaft bolt torque from 65 ft/lbs to 125 ft/lbs? One possibility is that loose timing chains can cause a harmonic resonance that creates high momentary torque loads on the cam and injection pump, resulting in sheared DS4 drive-head pins and loosened camshaft bolts.

    If a gear-drive timing set added torsional or impact stresses to the timing set and crankshaft, the problem with loose camshaft bolts and sheared injection pump drive-head pins would increase in frequency. As of 2006, our gear-drive equipped 6.5TD Project engine had accumulated over 250,000 miles without a problem of any kind, even though the camshaft bolt in this engine was torqued at the originally specified 65 ft/lbs.

    Depending on where you shop, a new chain/sprocket set could cost between $75 and $125. On the other hand, a gear-drive costs ~$250 (mechanically injected 6.2/6.5) to ~$350 for a Phazer gear-drive set made to operate with the electronic 6.5 fuel injection system. A gear-drive makes the most sense for the enthusiasts among us or for anyone who traditionally keeps the same vehicle for several years. If you tend to trade vehicles every 2-3 years, then a chain-drive timing set would make the most sense.
    TDP
    Last edited by More Power; 12-01-2021 at 12:16.

  2. #2
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    I have been looking for one of these, however I dont know where to buy them.
    I am looking for the cheapest I can find any ideas on where to buy the gear drive.
    93 GMC Sierra 2500
    6.5L TD 5 spd Manual trans Sold

    97 Chevy Silverado CrewCab K3500 Dually
    6.5L TD Auto


  3. #3
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    Quote Originally Posted by 93GMCSierra View Post
    I have been looking for one of these, however I dont know where to buy them.
    I am looking for the cheapest I can find any ideas on where to buy the gear drive.
    Diesel Services Group (www.dieselservices.com) was the originator of the gear drive timing sets for the 6.2/6.5. At some point during the last few years, 6.2/6.5 gear drive timing sets have become available through a few national mailorder auto parts vendors - for less money. I don't have a link for one of them, but I'm sure someone else will post it. I don't know if there's a difference in gear drive design, fit or quality between the two sources.

    Jim

  4. #4
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    I found DSG on the advertisers page of all places huh
    They actually have the cheapest price of the ones I found. I am unsure if the $450+ is worth it. $225 or so as you listed it would be for sure. If I was doing a complete rebuild $450 might even be worth it but all I am planning is relocated new pmd, new "used" IP, new injectors, and glow plugs.
    at 195k for mileage and the serious lack of power and mileage this truck has I am guessing all the parts are original.
    I am getting many symptoms listed for these parts being worn. I keep getting a pump injector timing code. but its sporadic.
    Hard starting, 5 or more seconds of cranking, warm or cold. Cold starts are worse, lots of white smoke at start. Heavy diesel smell when starting and strong when running. I figure while I have it torn apart it probably needs a timing set. I will most likely get a new chain set. RockAuto has it for about $100.
    93 GMC Sierra 2500
    6.5L TD 5 spd Manual trans Sold

    97 Chevy Silverado CrewCab K3500 Dually
    6.5L TD Auto


  5. #5
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    Based on the symptoms you're reporting, a worn timing set could be a contributor. A new chain will likely help.

    DSG offers a gear drive for both the DB2 & DS4 equipped engines. If you have a 1982-1993 engine, you can use their standard "Dual Idler Gear Drive", which is about $100 less expensive than their "Phaser" gear drive, which includes a reluctor wheel for the crankshaft (that's why the increase in price).

    If you have an engine newer than 1994, you'll need the Phaser even if you are running a DB2. Or, you could machine a spacer to make up the difference for the thickness of the reluctor wheel. Or, install a damper made for a 1982-1993 engine.

    Jim

  6. #6
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    Quote Originally Posted by More Power View Post
    Based on the symptoms you're reporting, a worn timing set could be a contributor. A new chain will likely help.

    DSG offers a gear drive for both the DB2 & DS4 equipped engines. If you have a 1982-1993 engine, you can use their standard "Dual Idler Gear Drive", which is about $100 less expensive than their "Phaser" gear drive, which includes a reluctor wheel for the crankshaft (that's why the increase in price).

    If you have an engine newer than 1994, you'll need the Phaser even if you are running a DB2. Or, you could machine a spacer to make up the difference for the thickness of the reluctor wheel. Or, install a damper made for a 1982-1993 engine.

    Jim
    I still wish I had the 93. However this is the 97. Yes I am sure worn and excessive slack is a contributor.
    93 GMC Sierra 2500
    6.5L TD 5 spd Manual trans Sold

    97 Chevy Silverado CrewCab K3500 Dually
    6.5L TD Auto


  7. #7
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    Take a look at Pete Jackson gear drives . Supposed to make them for DSG .

  8. #8
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    A lot has changed since this post was last updated. Gear Drives were discontinued but now back in production. We try keep them in stock at all times as a US source for the DSG product.
    Kennedy Diesel-owner
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  9. #9
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    The hard starting with white smoke and such can also be caused by a set of worn out injectors.

    The occasional timing code is not a good sign though.

    The ECM will adjust the injection timing though a fairly broad range before it complains.

    Before spending the big $$$ for a gear set, I would suggest getting the Squirts checked.

    A strong diesel smell when warm is sign of bad injectors.

    If its a timing issue, the computer would complain bitterly.

    Hard cold starts, aside from bad glow plugs are directly connected to low pop pressure and a set of injectors that are Peeeeing a stream rather than a fine mist upon entering the injection cycle.

    This is a commonly overlooked problem which usually ends up with folks blaming the glow plugs.

    If your injectors are at 100K miles or more, they are suspect.

    With a set of squirts that are in good shape, these engines will start with minimal smoke even with half the glow plugs non functional.

    A long period of cranking followed by tons of white smoke and a period of time that the engine misses on a few holes, then followed by a strong pungent exhaust odor even when warm points more towards injectors than timing gears/chain.

    Having a timing set, either gears or chain and sprockets that's in good order is a plus for sure, and all the materials mentioned are definately spot on, I would still check your squirts before stepping up for the timing set.

    FWIW
    I have replaced chains on these and retained the original sprockets many many times. The sprockets are HARD and dont seem to wear.

    The chains stretch in time and as Jim mentioned, start to cause issues.

    I have seen engines with 250K miles and a chain that was looser than a rat tail in a rain barrel still run good without complaints.


    Missy
    (1) 1995 Suburban 2500 4x4
    (1) 1997 Astro
    (1) 2007 Chevy Avalanche
    THIS IS BOW TIE COUNTRY

  10. #10
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    I had a gear set on my old 6.2 engine that broke a crank (not bc of the gear set). I put a different 6.2 engine in the truck and installed a new gear set that a friend of mine bought for a 6.5. I bought a whole box of new/used parts from him when he sold his truck. The gear set was new and since mine had more than 200K on it I decided to put the new set in. It had the reluctor wheel with it but I didn't use it and I used my long snout balancer. Is there any difference in the gear set itself between the 6.5 and 6.2?
    Bill Efland
    83 C10 6.2TD Short Bed
    befland@yahoo.com

  11. #11
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    Default

    Quote Originally Posted by befland View Post
    Is there any difference in the gear set itself between the 6.5 and 6.2?
    Not to my knowledge (other than cost). The reluctor added about $100 to the cost of the Phaser compared to the non-EFI gear set.

    Jim

  12. #12
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    Quote Originally Posted by befland View Post
    I had a gear set on my old 6.2 engine that broke a crank (not bc of the gear set). I put a different 6.2 engine in the truck and installed a new gear set that a friend of mine bought for a 6.5. I bought a whole box of new/used parts from him when he sold his truck. The gear set was new and since mine had more than 200K on it I decided to put the new set in. It had the reluctor wheel with it but I didn't use it and I used my long snout balancer. Is there any difference in the gear set itself between the 6.5 and 6.2?
    Quote Originally Posted by More Power View Post
    Not to my knowledge (other than cost). The reluctor added about $100 to the cost of the Phaser compared to the non-EFI gear set.

    Jim

    That is correct. A gear drive is a gear drive. It becomes a phazer when you add the phazer ring. The injection pump type and the balancer snout length determine whether you need a phazer or not. The electronic balancers have a shorter snout so they would require a phazer to fill the void if used on a mechanical engine.
    Kennedy Diesel-owner
    More than just a salesman-I use and test the products that I sell on a daily basis!
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  13. #13
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    OK, let me get this all straight before I order the wrong thing, I am going with a GEP motor, ( ordered it today) a military take out 6.5, I have a DB2 pump, and will order a Fluidampr for a manual pump motor, and order a gear drive for a Manual motor ... am I right??

    Thanks, Chris
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    Quote Originally Posted by sctrailrider View Post
    OK, let me get this all straight before I order the wrong thing, I am going with a GEP motor, ( ordered it today) a military take out 6.5, I have a DB2 pump, and will order a Fluidampr for a manual pump motor, and order a gear drive for a Manual motor ... am I right??

    Thanks, Chris
    The Fluidampr produced for the mechanical fuel injection engines comes with a spacer to accommodate an installation with/without the reluctor. So, either way you'll be OK when using a mechanical gear set.

    Jim

  15. #15
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    Default Long term study of gears

    How has the long term use on these gear sets held up? Any long term tear down study conducted> I would be interested in seeing the condition of the gear teeth after 100k plus miles.
    1994 K2500 ext cab. Recently repowered with; Non-cracked 599 block, factory compression, used old DSG girdle for main caps. Factory for what remains. Changed diffs to 3.42. Fuel economy Hwy 22.5 mpg US, in town without lcokup in 2nd/3rd - 18 mpg US.
    1994 K3500 CC LB Silverado. Next project. Built for endurance, power and gearing. Plan on opened up intake and exhaust sytem, best cooling mods, 4.11 gearing 4L80E, followed by Gear Vendors OD. Need to be able to split all gears and have lockup in 2nd/3rd/4th. Tan interior cloth, Bad ass dark blue (coming) aluminum wheels and air ride (coming)

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    I have 90K on the factory (Peninsular Engines) AMG 6.5 TD. There was no sign of wear when I replaced the coolant pump at around 50K on the engine. These gears are VERY lightly loaded and in an oil bath, so wear should never be a concern.
    '94 Barth 28' Breakaway M/H ("StaRV II") diesel pusher: Spartan chassis, aluminum birdcage construction. Peninsular/AMG 6.5L TD (230HP), 18:1, Phazer, non-wastgated turbo, hi-pop injectors, 4L80E (Sun Coast TC & rebuild, M-H Pan), Dana 80 (M-H Cover), Fluidampr, EGT, trans temp, boost gage. Honda EV-4010 gaso genset, furnace, roof air, stove, microwave/convection, 2-dr. 3-way reefer. KVH R5SL Satellite. Cruises 2, sleeps 4, carries 6, and parties 8 (parties 12 - tested).

    Stand-ins are an '02 Cadillac Escalade AWD 6.0L and an '06 Toyota Sienna Limited.

  17. #17
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    Quote Originally Posted by rustyk View Post
    I have 90K on the factory (Peninsular Engines) AMG 6.5 TD. There was no sign of wear when I replaced the coolant pump at around 50K on the engine. These gears are VERY lightly loaded and in an oil bath, so wear should never be a concern.
    Do you have a gear drive or chain? The chain is highly loaded as it drives the cam and IP. Mine has 250K on it and its scary loose.

    I want a gear drive so bad but $500 with exchange makes it a hard pill to swallow.
    1984 Chev Get-A-Way van, 6.2 diesel, remote mounted turbo built by me, running an HX35 turbo with a 60mm wheel. Burning WMO, WATF, jet fuel and Hydraulic oil.

  18. #18
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    The DSG gear drives are no longer in production. We purchased the last of their stock and quickly sold out of the gear drive kits. We do still have some have phazer kits (just means extra parts for the mechanical guys) and when they are gone it will mark the end of an era.
    Kennedy Diesel-owner
    More than just a salesman-I use and test the products that I sell on a daily basis!
    Superflow Lie Detector in house
    2002 Chev K2500HD D/A CC Long LT 11.77@ 124mph at 7700# fuel only-e.t. needs help
    2005 Chev K3500SRW D/A CC Long LT(SOLD)
    2007 Chev K2500 Classic EC Short LT (Sold)
    2012 GMC K3500SRW D/A CC Long LTZ Happy Birthday to me! Built 1 working day after my birthday and delivered 7 days later.
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  19. #19
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    Unhappy

    Quote Originally Posted by Kennedy View Post
    The DSG gear drives are no longer in production. We purchased the last of their stock and quickly sold out of the gear drive kits. We do still have some have phazer kits (just means extra parts for the mechanical guys) and when they are gone it will mark the end of an era.
    Bad news for the 6.2/6.5 crowd. But then, the DuraMax was supposed to make these engines obsolete overnight . . . . NOT.
    Dr. Lee

    1984 C-10, custom 6.5L SAA, custom 700R4, Gone but NOT FORGOTTEN

  20. #20

    Default Gear Set

    I was told Leroys Diesel is making gear sets for these engines. I called and he claimed they are made in USA and are heat treated.

    FYI

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