gear drive timing gears?

[great white]

Pro's and con's please.

I'm aware of the ones on gassers, would like to know the opinions on the 6.5.

Discuss.

 

[SmithvilleD]

Think the main legitimate con is cost.

Theories circulate about gear drives transmitting more vibration & thus causing a higher crank failure rate.

Suppose that's possible, but there are quite a few 6.5's out there that have run the gear drive for 150k + miles.

You do gain tight, consistent control of timing for many, many miles. The vast majority of heavier duty diesels have gear driven cam timing.

I went w/ the gear drive because I didn't mind spending some $ at engine build time for better durability & lower longterm maintenance. I enjoy working on these projects when it's by choice. But failures/problems that force one to work on it whenever it happens take the fun out of the hobby.

They're expensive & not a necessity, so you have to decide if the benefit is worth the cost to you. If you're not gonna drive it 100k miles, it's probably tough to justify.

 

[Turbine Doc]

X2 with Smithfield

GW I went with gears on my build, all that I have conferred with that put gears in theirs was happy with them, when I install my engine if you don't beat me to it, I'll have personal experience with them, only 6.5 person I've seen say negative things about them is at that web site we were discussing before, and his opinions have been proven to be incorrect on multiple occasions.

I also went with a Fluid Damper more $$$ but since I blueprinted/balanced the engine I figured I'd spend the extra expense for the FD

 

[great white]

X2 with Smithfield

GW I went with gears on my build, all that I have conferred with that put gears in theirs was happy with them, when I install my engine if you don't beat me to it, I'll have personal experience with them, only 6.5 person I've seen say negative things about them is at that web site we were discussing before, and his opinions have been proven to be incorrect on multiple occasions.

Sure, I also ask because I remember reading a recent article in diesel power about heath's Bonneville truck using a 100 or 200 000 mile chain with minimal stretch on it.

Just wondering what benefit gears give in a diesel engine.

I guess it's essentially the same as a gasser IE: precise cam timing. Although, chains and belts do take some of the shock loads out of the equation...that is true no matter who says it.

Now, enough to break a crank?

I highly doubt that...

 

[Turbine Doc]

Better timing control, Kennedy reported better dyno performance after installing them, but I never got into it deep, buddy of mine went to a Cummins or scrapped his DS4 I don't recall the circumstance now in his ride and could not return them.

I was doing a build he had some miles on them he sold to me at a discount. fresh chain/gears would probably serve just as well, my current engine has 212K on it with original chain actual & desired timing still match up good on acceleration/deceleration so no significant stretch

 

[schiker]

TD I will propose that its somewhat related to health of IP if timing chain wear will affect things. My logic follows from these thoughts....

Heath doesn't really support that timing gears are better and his race truck uses a stock chain. But his IP and electronics are highly tuned.

Hot rod gassers for a while went to gears to better control precise/accurate spark timing.

But with the advent of electronics and spark timing more or less independant of cam timing; cam drive has gone to belt drive to reduce rotating mass for drag racing. And uses spark timing controlled electronically referenced to crank time and thus more accurate. Valve timing is imporatant but not as important as precisely/accurately controlled spark (combustion) timing.

Well to me that means a gear drive can hold more accurate mechanical time relation than chain (or belt) but if the timing is electronic in nature who cares.

The DS IP is a combination of electronics and mechanical time so better mechanical timing in my mind makes it easier for electronics to control because there will be less corrections. And the resolution of electronic measure is limited so with better time control there is some advantage.

Does it transfer more acceleration forces and stress to the IP/cam drive maybe??? and that is the theoretical con. But with good harmonic balancer (or better than stock fluid dampener) that should negate most or all of the theoretical draw back of gears. Then as posted earlier its mostly an economic pro/con.

With chain I think its even more important to keep good grounds, voltage, wiring, and fuel quality in check so its easier on electronic controls/correction mechanisms.

And maybe the chain is easier to accelerate so in a drag racing accelerating speed racing differences chain is better but in towing and steady state speed varing load and deceleration ie going up and over hills a gear drive is more accurate and has better performance for same good healthed electronic controlled DS IP.

 

[great white]

TD I will propose that its somewhat related to health of IP if timing chain wear will affect things. My logic follows from these thoughts....

Heath doesn't really support that timing gears are better and his race truck uses a stock chain. But his IP and electronics are highly tuned.

Hot rod gassers for a while went to gears to better control precise/accurate spark timing.

But with the advent of electronics and spark timing more or less independant of cam timing; cam drive has gone to belt drive to reduce rotating mass for drag racing. And uses spark timing controlled electronically referenced to crank time and thus more accurate. Valve timing is imporatant but not as important as precisely/accurately controlled spark (combustion) timing.

Well to me that means a gear drive can hold more accurate mechanical time relation than chain (or belt) but if the timing is electronic in nature who cares.

The DS IP is a combination of electronics and mechanical time so better mechanical timing in my mind makes it easier for electronics to control because there will be less corrections. And the resolution of electronic measure is limited so with better time control there is some advantage.

Does it transfer more acceleration forces and stress to the IP/cam drive maybe??? and that is the theoretical con. But with good harmonic balancer (or better than stock fluid dampener) that should negate most or all of the theoretical draw back of gears. Then as posted earlier its mostly an economic pro/con.

With chain I think its even more important to keep good grounds, voltage, wiring, and fuel quality in check so its easier on electronic controls/correction mechanisms.

And maybe the chain is easier to accelerate so in a drag racing accelerating speed racing differences chain is better but in towing and steady state speed varing load and deceleration ie going up and over hills a gear drive is more accurate and has better performance for same good healthed electronic controlled DS IP.

Some interesting thoughts to ponder there ...

 

[SmithvilleD]

Their literature/install instructions also claim increased fuel economy (up to 5 mpg). If memory serves, they're designed w/ a small amount of cam & therefore also inj pump advance as compared to the stock roller chain/gears.

Now I think the scale that of claimed fuel economy improvement is rather exaggerated, it's not unreasonable to suggest it might show some measureable mpg gain when it's replacing a notably stretched chain.

I will say I've been impressed/surprised really with my engine/truck's mileage. I recently took a job that's a 75 mile, 2 lane ~ 60 mph daily drive & the truck's done btwn 20-21 mpg for 5 consecutive tanks now. Granted that's about the ideal top speed, air temps, & summer fuel conditions for best mileage.

There's a pretty strong correlation w/ too long oil change intervals/high oil soot levels and accelerated roller lifter axle wear. I wouldn't be surprised if the same type of wear happens w/ roller chains at high oil soot levels, just don't see the wear/failure as fast as on the roller lifters because the chain rollers arent' spinning nearly as much.

http://www.swri.org/4ORG/d08/DieslTst/rollfoll/default.htm

http://www.swri.org/4ORG/d08/DieslTst/rolfolow.pdf

 

[SuperTuscan]

I had a set for my 94 6.5TD and I can tell you it made a big difference in the way the engine ran. And, I changed them out when the enging had about 50,000 or so miles so there shouldn't have been that much of a stretch factor that the gears were correcting.

However, I did change the timing to -1.94 at the same time I changed the gears so there may be too many variables to attribute to the better running.

So, if you do both then I will say that you should experience the same crispness and higher rpm smoothness that I experienced when I changed them out. Probably more so if your chain is worn.

 

[SmithvilleD]

Should have added this link also, as it's the one that specifically describes the wear/high soot levels correlation.

http://papers.sae.org/922199/

This would seem a reasonable explanation of the highly variable amount of stock timing chain slop folks that have torn down a lot of higher mile 6.2/6.5's report. Some engines got more consistent (& shorter interval oil changes) than others.

 

[buddy]

I dont like the chain in mine, it seems sloppy to me. Timing isnt held well to the desired all the time. I get a large range in timeset and TDCO relearn. If I were rebuilding I would do gears assuming I had the money. Although, I also know its not necessary for big power, more of an efficiency thing I would think.

 

[SmithvilleD]

That's a good thought to look at timing a bit more analytically. Been a while since I've run w/ GMTDScan Tech open showing those screens so you can compare desired/actual timing.

If memory serves, I think they mirrored pretty close on my truck, but I'll watch this for a few days & report back so we can compare notes. This is another situation where I wish GMTDScan Tech could datalog.

Just observing the screen (& doing a few screen grabs) might give some sense of how well the PCM is able to control inj timing - t-chain - vs - gears? But the ability to go back over a 5 minute log & display the variance btwn desired & actual inj timing, step-by-step might well give a repeatable truly quantitative view of any timing control advantages the gear drive provides.

 

[SuperTuscan]

When I had my timing set to -1.94 way back when the tech doing the job commented on how tight the timing was. I guess there's some movement with the timing chains, even when new.

For me it came down to how accurately you want to drive the IP.