Well, I've heard enough different opinions to write a book about gear drives... But whats the real story? Aside from the noise like it or not thats not the question, the question is, does it hurt valve train? Does it improve HP because its gears meshing faster then a chain pulling? Does it really keep timing from going wrong? Or any other problem or benefit from having one BESIDES the noise factor people love/hate? Thanks.... (Thinking about buying one soon, want to know if smart investment)

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IrateN8
Northern California
1970 Malibu 307 Sport Coupe

In my opinion gear drives are for very exotic type motors.They are absoluty unessessary for a street driven machine. If you just want to throw money at your motor then by all means get one. But unless you intend to dial the rest of the valve train in down to a split hair it's a waste of cash that could be better applied somewhere else.
Harley

OK, here is the word according to Bill Jenkins. Some of you may remember him, in his book he says it transfers harmonics to the valve train and the cam. He used plain old nylon gear sets! But remember he was in the motor all the time and changing them all the time.

Use a good roller chain, Manley makes a nice one. If you want the noise use the gear drive.

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Wally
Gold #67
67 malibu

[This message has been edited by Wally (edited 08-08-99).]

IrateN8, I'll make an engineering analogy to turntables ( I know, a relic of the past). Back in my audiophile days, the best turntables were LinnSondek and Ariston and other belt drives. Why? Becasue the rubber belt helped isolate vibrations from the drive source to the platter. The "trick looking" tables and the cheapos were all direct drive. They trnasferred the vibrations through the platter. I measured wow/flutter on various platters, the belt ( even cheap ones ) were generally much more stable than direct drives.

the same applies to motors. Now, is the level of vibration significant to the engine? I don't know. Does it outweigh the stretch of the chains and/or belts? Good question. My point is gear drives aren't the panacea fix all they might seem.



[This message has been edited by Gene Chas (edited 08-08-99).]

My LS-6 purchased in 1989 had a nylon cam gear. I was really surprised by that. I never saw it in any of GM's Performance Parts Catalogs though. I don't know how durable it would've been...I swapped in a regular double roller.

The nylon cam gears were intended to reduce noise and they may have reduced the harmonics transfered to valve train as well. They ran quiet and most would last 100k +. After awhile they would become brittle and start to lose teeth. With close tolerances this could have been a problem. I can't figure why they would use one on an LS-6, the sweet sound of that big block would overshadow any noise a steel cam gear could have made.
FWIW I still have a belt drive turntable as well as the system it came with 25 years ago. It is now in the garage as it wasn't hi tech enough for the rest of the family. It takes up valuable space, but I can entertain the whole subdivision if I feel the need to. Can some body send me a tape of there BB with open headers, I can play it when the kid behind me sits in the drive and revs up the nasty sounding 4 cyl Nissan at 2 a.m.

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Philip Valentine
Team Chevelle Member #42 GOLD
philip@chevelles.com

I have a 427/435 cam, lifters and gear set NOS, the gear is nylon for this combination. GM made a gear dirve, two gear style so the firing order is backwards. I think the cam gear was aluminum, I don't remember the application.

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Wally
Gold #67
67 malibu

The Chevy gear drive was used on the tall deck truck engines. Cam gear is (was?) 3964043, crank gear 3860086. The camshaft spins backwards, requiring a different distributor, and of course the camshaft had the lobes ground to compensate for the reverse rotation. You could also buy, from GM, reverse rotation L-88 grind camshaft 3925533.

I wouldn't bother with a gear drive of any sort unless you were using an unbelievably rough cam, and the complimentary ultra stiff springs, or planning to compete in Nascar events.

nascars use timing chains.67rat member #199

Remember that with timing chains you have contact spread over many teeth at once, whereas with a gear drive the contact area is always maybe 2 teeth. BTW, my lowly Chevy inline 6 came stock with counter rotating gear drive & nylon gears! (like all Chevy L6's)

Chevy offered a reverse rotation L-88 cam?? News to me. That must've been back in the day.... http://www.chevelles.com/forum/smile.gif It's amazing the things to be learned here. And FWIW, unless you like fine whine, can't see the big need for a gear drive. Though I'd be curious to know Grumpy Jenkins' theory about harmonics is true.

[This message has been edited by Larry (edited 08-10-99).]

Hell I like em.

I dont like em when they're obnoxiously noisey though. I have one in my small block.. probably would do like Harley said if I built the motor though, and put the $$ else where and just run a good double roller chain.

as for the harmonics thing, I dont think it makes much difference but i'd say the gear drive (dunno about nylon,talking about steel) will outlast the chain by twice the mileage or more.

Mike

mike
you nailed the head right on.did you ever have a chain jump or break?all that hurt,on all that money. I dont like to take the hole front of my motor apart just because the chains shot, although sometimes they do last as long as the engine.good day. 67rat member #199

I would like to run the Jesel belt drive, but the dollars kill me! Comp cams make the same deal for a little over $300. The Jesel setup is over $600. The belts are made out of the same kind of material that blower belts are.




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Wally
Gold #67
67 malibu