direct drive timing

Ford's been putting them in straight sixes for years, I know I have seen them in in-line 6 chevys since probably their inception. They use a fiber cam gear to reduce noise. The only headache is, in most cases the cam gear is pressed on & you gotta tear it completely out to affect a proper replacement. Don't see many go bad, though, must be why they stick with it.

The timing gears in the old 4 cylinder engines in the Fiero (and many other cars) were phenolic. They appear to be okay but failure isn't a if, it's a when just like any other timing component. They will wear out. In the case of these, the teeth will eventually get chewed off.

-Bruce

Respectfully, Bruce, I had an 84 Fiero with the Iron Puke 4 cylinder engine. It did not have phenolic gearsets.

The inline six Fords almost never had a problem with the timing gears. Most would outlive the engine and an overhaul. The reason they are not used more often now is the requirement for a fairly heavy valve train resulting in reduced RPM potential and less-then-optimal timing capabilities related to emission control. The overhead cams are more efficient and are reliable with proper cam drive design.

Lugnut

As I remember it, Lug, noise was the chief complaint about some of those engines with steel gears. Certainly wasn't valve train drive longevity.

The nylon gears that were sometimes used were quieter, but tended to shuck teeth at awkward moments.

Some racing engines have used direct drive to power both pushrod and OHC situations, if I remember correctly. Strength and accuracy are two advantages, but as you indicate, rotational mass effects may be more pronounced.

I am constantly impressed by the technology going into Formula 1 engines. To make an engine that can hold up for two races without being touched, at RPM's of 19,000 for a couple of hours per race, is quite an achievement.

You're right, I can't say all of them did. I was just saying that there are other cars out there with phenoic gears. My impression was that they worked just as well as a chain or belt. That's what I was trying to get at.

Studebaker was using these back in the 1950s. Made of a material called "Celeron" they look a lot like the stuff some carb spacers are made out of. Some of the high performance engines used an aluminum cam gear however, I guess high revs and high spring pressures can prematurely strip the teeth on the fiber gears.

nate

You want gear noise, listen for gear drives in small block Chevies or Fords. We put a Pete Jackson set in a Bronco with a blower a few years back. It sounded kinda cool but, most regular folks wouldn't tolerate it for a minute. Also, it is quite common to use gear drives for cam-in-head engines. Detroit Diesel and others have used it in heavy duty engine for decades. It is durable, strong, reliable, accurate, expensive and complex for most automotive applications. In this arrangement, the reliable RPM potential is greatly enhanced. If you have the cam in the block like most auto engines have had over the years, you need a relatively heavy valve actuation system making it more difficult to achieve higher RPM and maintain timing accuracy.

A few years back, I worked the tech crew at Road Alanta for a while. It was unreal what some of those cars in the pro classes could do. One of the finest sounding engines I ever heard was a Farrari 3L 12 cylinder strung out at 13K with the owner complaining the driver had no balls to drive the car.

Lugnut

There is nothing quite like one of these engines moaning into the +10K range. Pity I was born poor.

My experience with phenolic gears has not been so good. They are a bit 'soft'.

Belts and chains have their limitations as well. But you can't have everything in one package, I guess.