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gear drive

ak diesel driver

ak diesel driver

6.5 driver
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Location
alaska
Talked to Bill Heath today and found out he didn't care for gear drives. Wasn't a crankshaft issue for him though. He said that it transfered crankshaft harmonics thru the cam and to the IP. Also said he's seen quite a few fail. Any other thoughts or opinions out there.
 
This is the kind of question I wish there was some legitimate polling/statistics on. I thought about this a fair bit while deciding what components to use in my engine project. I ended up going with the gear drive/phazar wheel.

Without some statistically significant data, 'ya have to go, a lot, on opinions & anecdotal info. If the gear drive's fail in some significant % of installs, one would think it's got to be some 6.5 specific factor/cause.

Gear driven cams are used far more widely in diesels than timing chains. Virtually every diesel tractor I've worked on with the Roosa-Master pumps had gear driven timing.

There's an article in Jim Bigley's TDP manuals that mentions GM made a revision to a higher grade bolt & higher torque specs for the cam gear/sprocket at some point. You'd think GM had a reason, but without documentation, we sorta have to speculate why.
 
~ 1500 miles, so not enough to be meaningful. The engine runs well thus far, so no complaints, but I would expect that with a new timing chain set also.

I did install a Fluidampr & balance the rotating/reciprocating assembly. The Fluidampr could help limit damaging harmonics. I also had the injectors I used tested by a friend to comfirm their pop pressures were tightly matched.

With all the discussion about crank failures & harmonic balancers, I surprised cyl to cyl power balance doesn't get discussed much. The endurance race engine builders focus quite a bit on power balance saying it's key to keeping a crank alive when run near its limits - their goal is to have the absolute lightest rotating/reciprocating mass possible with no failures.

Given Bill's comments, I wonder if he's seen something in a tear down of a failed engine, or just enough correlation of failed engines w/ gear drives to be weary of them. No doubt there are a lot of 6.5's that ran to 200k miles + on the timing chain - regardless of it was sloppier towards the end than a gear drive.

The last of the TDP Manual's 6.5TD Power Project truck went 200k miles w/ the gear drive so there is an example of long-term durability.
 
Bill claims they will last to 300k and reused the one on his land speed racer. It would also be interesting to know more actual data on the fluid dampner there's alot of differing opinions on that also.
 
I think i side with Bill heath on this. If it was a a setup like on most diesels with the idler gear on its own shaft/brg it would be OK.
IMO, the floating gears like the phasar would prob cause more vibration from the get go than a worn chain would.
One can replace a lot of chains for the price of 1 set of gears
 
I already have the gear drive was wondering if it's enough of an issue to not put it in. Or if a fluid dampner would kinda compensate for it.
 
I could definitely see the chain passing a lower % of harmonics thru to the cam/inj pump. Then the question becomes does any additional vibrations transmitted by the gear drive cause problems. As Bison says, most diesel gear drives don't have the floating sort of idlers the 6.5 drive does.

My understanding is that viscous dampers were originally designed for the toughest harmonic balancer apps. I've got a link to a book excerpt that has a good couple paragraphs on the subject - can send if you guys would like.

Here's a small bit that directly relates to our thread. "An important consideration is the fitting of a tortional vibration damper to the crankshaft of a modern heavy-vehicle diesel engine is that of protecting the comprehensive gear train of its timing & auxilary drives from the vibrational disturbances"
 
Maybe tomorrow I'll call and talk to someone at Fluid Dampner. One of my ?s is what does extreme cold weather do to these things? Would it be like a solid chunk of steel?
 
Their literature says the silicone is not effected by temperature change.

I would hope that's the case because it's the silicone in the void that attenuates the vibration. That energy's gotta be going somewhere so I'd guess it goes to heat in the fluid.

These are the choices that challenge me. Unless there's a clear understanding of cause/effect like has evolved solutions like the PMD heat sinks - you ends up pay'n 'yer money & tak'n 'yer chances.
 
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I do wonder what the cause of stock damper failure is to start with? Is it the damper giving out on its own ?,or is it crank/piston assemblies imballance that kill the damper?
I got a 6.2 with 700 k on the original damper,it looks still as good as new.
i got 3- 6.5's + 1 more 6.2. all the dampers have between 250 and 340 k on them and they all look good,no cracks or loose rubber.
 
Don't have much miles on my gear drive, yet. But I did it under advisement from my engine builder - who has been running one for many, many miles - and John Kennedy. They both said it's a good upgrade. I'm not discounting what Bill says, but as mentioned above, until there's actual evidence of a problem being directly related to the gear drive, I'd do it again.
 
I talked to someone at fluid dampner this morning and at least as far as cold weather is concerned it shouldn't be a problem. Said they use them in some aircraft appl where he said it got to -100*F. Don't know as I buy the -100 but I do know it can get to the -50s as you get up in altitude.
 
bison said:
I do wonder what the cause of stock damper failure is to start with? Is it the damper giving out on its own ?,or is it crank/piston assemblies imballance that kill the damper?
I got a 6.2 with 700 k on the original damper,it looks still as good as new.
i got 3- 6.5's + 1 more 6.2. all the dampers have between 250 and 340 k on them and they all look good,no cracks or loose rubber.
Click to expand...

The damper info I mentioned comes from a book called Light and heavy vehicle technology by Malcolm James Nunney - 2007. Here's what he wrote regarding rubber dampers.

"For particularly arduous duty such as may be encountered in the larger sizes of automotive diesel engines, the rubber damper can have certain limitations with respect of its durability, since the high damping forces involved could result in overheating of the rubber element. A viscous damper, so called because the damping forces are generated by the drag of of a very heavy or viscous fluid, is of generally more rugged construction and may therefore be the preferred choice for these applications."

These dampers are to attentuate tortional (not rotational) crank vibrations. Meaning the small twist/untwist of the crank each time a cylinder fires. And if I understand the term "harmonic" correctly, these vibrations tend to be most damaging at certain vibration frequencies where the assembly naturally tends to resonate.

Suppose the OEM dampers fail from their individual combination of aging rubber, vibrational heat load, & maybe individual mfg quality.

Regardless of all the science/logic, watching the 6.2's accessory drive v-belts vibrate/bounce is one way to actually see something visual that relates to the tortional forces at work.
 
If anyone get's any more info on the gear drive, please post it up. I was planning on a set for the build, but now I want to make sure they won't have a negative effect on anything.
 
For the 92-93 6.5 guys you can run the Pete Jackson gear drive for the 6.2, its alot cheaper. The mechanical IP vans may be able to use it also, as long as it dont have a crank sensor in the timing cover for the TCM.
 
I have about 20,000 on mine now with no issues. I did notice that after it was installed it idled better and runs smother. As stated above all heavy duty diesels use gear drive for longevity and accurate timing.
 
thanks for the heads up on the pete jackson setup. looking to keep cost down as much as possible without compromising any quality :thumbsup:
 
I took two 6.5 cores apart this winter that had gear drives in them. One I know for sure had over 250,000 km on it and the other I am unsure of because the guy that owned the truck did not put it in, it must have been a previous owner. Both were in as new-condition, and it is not the only two I have come across in used motors.

The only dual idler gear drive I have ever seen that failed was an Edelbrock setup for a SBC in a early-mid sixties 283 that had been line-honed and the owner did not make sure there was enough clearance when he installed the kit. The new timing chain was too loose so he bought the gear drive hoping to cure the issue, that itself should have been enough of an indication that there was a problem. In the end he had to replace the main and camshaft bearings and put in a different timing chain into the engine. The gears turned a bit blue but he ended up putting the gear set into a 350 in a grain truck anyway and it is still in there last time I checked, lasting three years so far.
 
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