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Discussion Starter #1
im buying a motor from a friend and it is just about stock but freshly built. forged pistons (probe) 7 quart oil pan, crank scraper, molly rings bearings, crank turned. cam, that's about it.
my questions is ,,,,, what is i want to put a gear drive on this car? will it help me out or slow me down. i love how they sound that's why i want them. im also going to put heads on this motor along with some 1.7 roller rockers i already have to slap on it.
i hurd that EFI cars dont run well with gear drive!!!!! anyone know whats up and if i can do it with out a problem? thanks
 

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you can do it without problems but i'd spend the money elsewhere. the performance gain would be minimal IF at all. seems like a lot of money for the sound to me, but if you really like it go ahead.
 

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DONT!!!
It causes harmonics and thats what kills the life of engines. If you want to spend that kind of money on that part then buy you the Australian billet one that Holcomb Motorsports sells. Now thats worth the money....
 

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well i still would like more post's on this topic. im still not sure if this is a good after market part to add to my car or if it is just a waist of money. i have the motor all torn apart so its not going to be herd to install the gear drive if i do buy it. im really in love with the sound it gives. but if you all say it is bad for a motor then i wont get it. help me out thanks.
 

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Gear drives can be a very accurate method of driving your cam but they were designed for a purpose and do have some downsides to using them. The best reason to run a gear drive is for sprint cars where you will be driving your oil pump and fuel pump directly from your camshaft and belts or chains would be stressed too much. The good quality gear drives like the shaver wesmar are gonna cost you around 500 dollars. The cheap noisy ones are best used as door stops in my opinion. They are designed to make alot of noise to impress the street kids. Just keep in mind that sound is caused by vibrations and those vibrations are directly transferred throughout your valvetrain and engine. Vibration is the enemy of valve trains. Im not sure if it would affect the knock sensor on EFI cars. But I would never use one anyway so... the choice is yours.
 

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I agree with Dano, They will over time kill your valve springs due to the transfer of harmonics. With this said if you want to be different buy a Jesel belt drive system, They are only about a grand but they are far superior to gear drive.
 

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The idea of the gear drives causing damaging harmonics is only theoritical. I've never heard or seen any data that about an engine failure that could even remotely be blamed on a gear drive. The best way to avoid this micro possibility is just to simply not buy a 'noisy' gear drive. Gear drives may not be necessary if your running a small cam (under .600 lift). Anything around .600 or more the valve spring pressures really start loading a timing chain and will stretch it all to hell in a short period of time. I've seen it happen to many times. I've had racers call me several times complaining about a drastic loss of power and that they can't set the timing on their relatively new engine they just built. Every single time it was a stretched timing chain. It didn't matter what brand or what type, they all looked like wet underwear hanging on a clothes line when you pulled the timing cover. I've been using gear drives for years, known people who have, and none of them have ever had single problem that was gear drive related.
 
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Ever hear that gear drives cost you about %10 on your HP? It's on here, with supporting data somewhere.
 

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I guess harmonics must just be something they play down in Alabama. Gear drives WILL transmit the vibration and harmonics directly from the crank to the cam, lifters, pushrods, springs, and valves. Don't believe it? Think about your rear differential, it is geared (obviously), and every time you roll on or off the gas, any vibration from the gears is transmitted to the rest of the car. And that's with a helical-cut gearset, not the straight-tooth like on the gear drive. Or, just draw a direct line, straight through all the metal from the crank gear, up through the idlers, through the cam gear, and on to the cam and beyond. A chain won't transmit as much of that vibration because of a little slack, and there is not a direct line of transmission for vibration. Your best bet? Get a belt drive. They transmit almost zero vibration, are easy as cake to adjust cam timing with, and last almost indefinitely. Its a pricey choice, but it depends on how reliable you want it to be.
 

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ive seen them first hang ovalize bearings. i would never put one in my street driven car.

if you want to spend the money on something that will give you the noise, BUY A BLOWER. there is no substituting that noise.

get either a FMS 9 keyway timing set or belt drive.

also, are you sure the 1.7 rockers will work with the cam (and heads), and pistions on that engine? thats something to look into.

take care,
adam
 

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streetwarrior said:
I guess harmonics must just be something they play down in Alabama. Gear drives WILL transmit the vibration and harmonics directly from the crank to the cam, lifters, pushrods, springs, and valves. Don't believe it? Think about your rear differential, it is geared (obviously), and every time you roll on or off the gas, any vibration from the gears is transmitted to the rest of the car. And that's with a helical-cut gearset, not the straight-tooth like on the gear drive. Or, just draw a direct line, straight through all the metal from the crank gear, up through the idlers, through the cam gear, and on to the cam and beyond. A chain won't transmit as much of that vibration because of a little slack, and there is not a direct line of transmission for vibration.
The main webbing of the block is more directly connected to the cam than a gear drive. How are you going to stop the harmonics transfered from the crank, to the cam and beyond? The gear drive, as I have explained before, is not directly connected to the valve train. There is several thousandths clearance between the gear teeth for oil. Most of the vibrations, if there were any to amount to anything, would be lost within the oil clearances.

My theory (and I'm probably right) is to what started this whole thing about gear drives causing valve spring and other valve train problems is once upon a time, some "Billy Bob" somewhere had a cam that was way to agressive for his engine. "Billy Bob" kept stretching the hell out of his timing chains so he swapped to a gear drive. Well, that solved the stretch problem but by this time the overly agressive cam lobes started taking their toll on his valve springs and the rest of the valve train. SO what does 'Billy Bob" do? He blames it all on his gear drive and the rumor spreads from there. Sound about right?
 

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Nope, but then I run probably some of the most aggressive springs on this web, and Ive never seen a chain streetch. I guess its just differnt out east. Maybe the humidity....

The iron around the main webbing, and around the cam journals is static. It can transmit sound, but not physical vibrations.

The end of the crank, and crankshaft in general is not (when the engine is running). It flexes up and down, side to side, hell its moving several thou in all sorts of directions. Thats why they harmonic balancer is hanging out there (at the end of the crank shaft) it dampens those "harmonic" flexes.

The air gap between the End of the teeth may be a couple thou, but the teeth that are doing the driving are in as direct contact as they can get. Its more a side load, but there is also some verticle friction as the straight cut teeth mesh. The OIL film is only that wich is splashed on the gears, and a fair amount is slung off. I would wager the film left coating the gear is less than .001 thick.

The elastimer band on your balancer has about .050 clearance (thickness) obviously the end of the crank is feared to have a pretty signifcant deflection.
 

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Yes, and if you get a chance to test engines on a Dyno you will be able to see the effect of hitting the natural frequency of the springs and valvetrain when the power takes a dive at the certain rpm where this frequency is strongest. Adding vibration to the system can only worsen the problem and add to the wear and tear on the valvetrain. Next time you go to the track try to see who is running gear drives and who is running chains or belt drives. You may find a few street goofs running them of some blower car with mechanical injection that runs the fuel pump from the front of the cam but thats about it. Running pumps from the cam is the main reason these gear drives are run and then it is a fairly pricey high quality set that makes as little noise as possible and runs extremely smooth.
 

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If I were running an engine that I was planning on disassembling and inspecting regularly then I wouldn't hesitate to use a chain. By the time the chain begins to stretch a little, more than likely you'll have the engine apart anyway so replacing it wouldn't be as big an issue, plus they are much cheaper. However, if your not planning on tearing the engine down regularly I see a gear drive as a more practical choice. Even if it actually did cause slight problems (which I have never experienced), which is worse? A stretching chain that most definitely will cause problems, or a gear drive which MAY create slight harmonic transfer? I venture to say the gear drive would be the most logical choice, unless you don't mind pulling the timing cover with the engine still in the car on a regular basis.
 

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I think broken valve springs are a bigger issue than a chain stretching. IF I were to notice a change in the timming of the engine, and the marked distributor had not rotated, I would/could easily change a timming chain combination. When you notice the damage valve train harmonics can cause..... the valve has probably already met the piston, and a cheap fix would be a new valve.
 

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I will never ever use another gear drive. I used one for 3 years in a 351 cleveland. I bought one because i wouldn't have to worry about streching chains. Well let me tell you i didn't have problems till later. I was using a Pete Jackson and the way they are installed on Fords is using a bronze spacer between the cam sprocket and the thrust plate. After time that spacer wore down and caused my cam to walk in the block.

The first thing that happened was my timing kept changing and i couldn't figure out why. Then the distributor gear, gears were sheared off. First thing i thought was piston to valve contact or hydralic lock in one of the cylinders. So i checked everything over and found nothing. So i replaced the gear and about a month later it did it again. After tearing the engine down i seen the the cam gear was screwed up, thinking it was caused by the first gear that sheared, i replaced it. Once again about a month later it did it again. So i started looking into the gear drive, the bronze spacer had worn down a few hundreds and caused the cam to walk back and forth.

That gear drive cost me loads of money and i will tell everyone who thinks about getting one not too and spend money somewhere its worth it.
 

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wait a sec dont you put the btonze spacer between the cam geer and the thrust plate? If i remember correctly that what the instructions said and it seems like it would be alot safer that way
 

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Its safer running a good double roller chain or quality belt drive system. Than possibly replacing, cam, lifters, distributor gear(s), and risk dropping a valve cause the lifter dropped off the cam because of it walking. So with that in mind i'll never run a gear drive again.

After i replaced the gear drive in the cleveland i never had anymore problems with timing or gears. The same engine has been running street and race duty for the past 7 years with no problems other than the gear drive. So don't count the old Cleveland out, its a good strong running engine.

And I'm out...
 
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