Are gear drives stronger than timing chains?

I hear statements like this all of the time; "I run a gear drive because I'd break a timing chain". That's an interesting statement because I've never seen a timing chain break unless it was ancient and completely worn out, or something catastrophic happened to the engine. If someone's engine is actually breaking timing chains, then obviously something's not right. It isn't the timing chain's fault, and it certainly isn't because the engine is "too radical".

In 99.9% of engines, a good double roller timing chain will endure pretty much everything you can throw at it. If you're really wanting something nice, a billet timing assembly is a nice way to go such as what's seen in this picture. 

On big, bad to the bone, serious engines making 1,000 to over 3,000+ HP, I used Jesel belt drives, which is a RUBBER timing belt spinning a cam that has a tremendous load on it with ultra heavy, triple valve springs with 3 and 4 times the spring pressures than any basic performance springs have, and with cams that have lifts in the .850+" area. If a rubber belt doesn't break, neither will a good steel chain.

Don't get me wrong, there's nothing wrong with running a gear drive if you like the sound of them. I've installed dozens of them over the decades at the customer's request. They were especially popular back in the mid to late 80s. I just don't prefer them over a chain because the gear drive "whine" can get pretty old and annoying after a while. I like to hear the natural sound of the engine.

So with that, people who say their 350, 400 or even 500+ HP engine would break a timing chain is pretty funny when I have never had a failure with a timing chain in engines making more than twice that amount of power. 

The next thing I hear a lot of is that gear drives keep better timing than chains, which is simply hogwash. They say this because chains stretch. Yeah, well do you think gears don't wear? Not to mention, you aren't going to be running hundreds of thousands of miles on a serious performance or race engine to even worry about chain stretch because they don't go that far (in most cases if it's a "real" race engine). Cams and lifters don't last that long either... including roller systems. Not when you have a serious engine anyway. 

What really kills timing chains isn't RPM or how much power the engine makes. Believe it or not, what actually kills timing chains is IDLING. Yes, you read that right... idling! When an engine is accelerating, the load is continuous and going in one direction. Like a tow strap or chain. If you're towing a vehicle down the highway using a chain or a strap, the load is continuous and isn't hard on the strap or chain. Now stop, back-up, make some slack and then take-off. That sudden jolt or "impact" is what will break a tow chain or a strap if it isn't strong enough. Timing chains are no different, and when an engine is idling, it is not under a smooth, constant load. In fact, if you were to really look closely at what is happening with an idling engine, it is actually accelerating and decelerating in quick, small increments which wreaks havoc on chains because it's pulling, slacking and pulling again, but you can't see it, or it's hard to with the naked eye. 

Just watch your tachometer when you are idling. It doesn't stay at one exact RPM the whole time. It's bouncing around between 50 to several hundred RPM at a time as it's trying to sustain itself from not accelerating, but not dying either. You can really see this when using a digital tachometer, like one used for tuning purposes. It's constantly changing, yeah, well so are the loads being put on the chain. It's constantly yanking on it and relaxing it several times every second it's running. That's what kills timing chains. Like valve springs. Compressing one isn't what hurts them. It's "cycling" them that does. The same for firearms magazines. Leaving one loaded for years does nothing to the spring. This has been proven many times over by the best of the best in the magazine manufacturing business, from Magpul to Wilson Combat. What kills your magazine spring from feeding the way it did when it was new is cycling ammo through it. Valve springs, chains, straps or pretty much anything that is being cycled do the same thing. 

Now, some people will argue that a gear drive helps to create or dampen "valve train harmonics". You know what else dampens harmonics? Things touching the camshaft and absorbing those harmonics. And you know what is touching a camshaft? LIFTERS that are under stiff spring pressure and that are pumping oil, both of which help absorb harmonics.

Gears are hard and solid. Hang a box end wrench and a piece of chain from a wire. Now take another wrench and hit both of them. The hard, solid wrench will sing with a "diiiinnnngggg", but you know what the chain is going to do? "Thud"... because it absorbed any harmonics. Now hold another wrench against the hanging wrench. It won't ding now because the harmonics are being dampened by the 2nd wrench touching it. Now dip that hanging wrench in oil and it will dampen it even more. My point is that camshaft "harmonics" is a non-issue because too many things are dampening them, from the cam journals in the block, to the oil that's covering it, to the lifters, etc. Again, it's simply a non-issue. 

In this tech tip I'm not trying to put down gear drives. I used to run them when I was a kid back in the 70s and 80s, and I've installed dozens of them over the years for customers I built engines for who requested them, but they were pretty much only for the sound and not much else. 

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