Gear drive versus chain

[trevore]

Hi guys

Is there an advantage in running gear drives instead of a chain. Is there a point you get with spring pressure that you should change to a gear drive.

Pros and Cons

Thanks

Trev

[pinkstuff]

ditch the gear drives altogether.google 'harmonics' and do some reading concerning its effects on an engine. if in doubt ,go to a belt e.g a jessel setup.

[POS Dakota]

I'm not an expert with a few hundred engines under my belt, but per what I have researched the only problems I have read about are regarding dual-idler geardrives causing breakage of the cam...but this could very well be bull. I do know for a fact many in the mopar community are using the single-idler geadrives from keith black for example with great success in expensive large cube engines.

I would think that if they were a problem we would see a lot more evidence to support how bad they are.
The only example I was able to dig up was on a cummins diesel making well over 2000 ft/lbs before the stock cast cam broke, but it may very well be another issue.

I will agree that a chain or belt is going to serve to dampen harmonics a lot better, but how detrimental these mysterious harmonics are is a whole different story....

I am using a single idler in my mopar smallblock. i guess we'll find out.

This has the potential to be an informative thread if people with more experience would chime in and give some words of wisdom. I find it an interesting subject.

[vincenelson]

On normal asperated engines I do like chains and belts over the gear drives. For a blown motor I like the gear drives. My blown Motor in my boat when cold liked to back-fire which would make me real nervous with what it would do to the timing chain and timing gears. Especially the timing chains with the multi notched bottom gear......

[PackardV8]

FWIW, in the February 2009 HRM (yeah, I know, don't believe anything you read in an advertising-driven rag!) did a test of timing chain, versus two different gear drives and a Jesel belt drive. There were slight horsepower differences, with the chain testing best.

Bottom line for me: Your results may vary, but I've seen more problems than benefits from gear drives and today wouldn't run one if it were free. When someone brings in a $99.95 Summit straight cut gear drive for a street engine, right away, that's a customer I don't want.

A high-budget-track-only race engine wants a belt drive. Anything else gets a chain. A blown boat which backfires when cold - you're on your own!

jack vines

[Dodge Freak]

Sometimes these engineers think too much and can't leave well enough alone

Nothing wrong with a good chain set up--or belts if they fir your engine.

[Dave Koehler]

IF one is desperate for the advertised extra horse(s) for a non pro car then use the rubber band.
IF one never wants to worry about stretch and have the ability to easily mount things to it, then a 3 gear set from Donovan, Milodon or RCD is the ticket.
Now,... if you have a combo that no 3 gear drive is available then the rubber band is the choice.

Let's see, I have a Muldoon and a Donovan for my BBCs and they are over 25 years old. Gears look new.

Used some of the Pete 4 gear drives back in the day. No big deal with drag cars. The idler gears did not survive circle track abuse though.

Having said that, racers can screw up a peanut butter sandwich so flip a coin.

[DeltaT]

Just out of curiousity, do the belt drives noticeably reduce mechanical engine noise?

Jim

[kirkwoodken]

First, notice in my sig I'm NOT and engine builder. I have experience with only ONE gear drive. A friend installed one on his SBC and went slower, and he asked me to help him figure out why. We took the drive off his engine and put it on one of my dummies, with
my crank and his cam. For finding TDC, I use two plates made into a large "T", which I put on the deck and touch with the crank throw to find TDC. This eliminates any error in piston pins or slop.

With the cam plug out of the rear of the engine, we fixed a degree wheel on the rear of his cam with a Mighty-Mite mag base. We installed a chain drive and took degree measurements for a baseline. ALL measurements agreed from the front of the crank and the rear of the cam.

Next, we installed his three gear drive, the make of which I do not remember, and set the lifter height at TDC the same distance as we did with the chain drive. Rotating through a few revolutions of the crank, the timing at the cam varied about three degrees from the reading at the crank. (Keep in mind, I did this in the 60's.)

I did not check the gear teeth with a divider head to see if they were made properly, but assumed they were not, since I found a variation and the variance was not there with the chain drive.

Again, I want to stress this: It was the ONLY gear drive I ever checked, but after reading Smoking Yunick's comments about losing power with three-gear drives, I could see there was of possibility of that happening.

I am not against gear drives as they have their place. I do not feel that a howling gear drive on a street vehicle is necessary or desirable. Chain drives work very well, can last over 100,000 miles, and have been used for over 100 years. I am particularly fond of Morse silent chain drives and feel that the uninformed magazine writers are mostly responsible for their demise. Although a silent chain may appear loose when sitting still, all slack is taken out of them while they are running. They also offer minimal power reduction and are good harmonic absorbers. Like the 50's, they were great while they lasted.

I think bicycle chains belong on bicycles, and the chain drives should be made to run two independent chains running a half link apart. Just an opinion.

[Moparious Maximus]

It all depends on the application, I'd say 90% of all the race motors out there do just fine with a "good" chain drive. With that said, the single idler gear drives like Milodon, RCD, Kieth Black, ect, are next to indestructable.

I've had a KB gear drive on our 572" blower motor for 6 years and it looks the same now as when I put it in.

I'm not a valve train expert but I am a racer that builds my own motors and when you push your parts hard enough I've always found some extra comfort in a gear drive.

[CREngines]

i seem to remember Reher Morrison claiming that the double idler gear drive was the fastest way to knock 20hp out of a small block chevy they had ever seen. gears are fine for blower motors, other then that ill stick to my cloyes chain.

[POS Dakota]

Getting back to one of my earlier questions...

Does anyone have any kind of insight or experience on damage from "harmonics?"
This is the one thing I hear repeated everywhere yet no one produces any proof.

Anyone?

[kirkwoodken]

Another observation. It takes power to make noise. The fact that noisy gear drives are made points to the fact that they are less efficient than something silent. Many cars used silent helical gear drives, such as BBC trucks, and they held up well and were quiet. I'm not saying gears are as efficient as chains, as they aren't. But they can be quiet, strong, and long lasting.

[af2]

No PROOF Just what I have seen on sprints for the last 30 years. I need to talk to Dave on what he has seen at this point.
Most Sprints don't run any type of balancer and the mains are pretty amazing how they beat themselves up.

[Big Rat Attack]

Volume 2 engine masters did a cam drive comparison on a 440 mopar. milidon fixed idler, cat copy of the pete jackson dual idler, comp cams adjustable timing chain set, jesel belt drive.
total hp, timing chain 633.5 hp. miliodon 636.3 hp, dual idler 634, jessel 633 hp.

average hp, chain 596.4, fixed gear 596.3, dual idler 596.3, jessel 594.2.


But when you open up your 3406 cat diesel big time harmonics transfered up through the crank for one million five hundred sixty thousand miles. You look at the cam, lifters all the gears. Gears also driving a big compressor and mechanical bosch fuel pump and water pump. The cam lifters gears look like they just left the factory. Its impressive.

Look under the hood of an 18 wheeler watch that engine set there and do harmonic vibration city lol.