gear drive instead of timing chain..
12-30-2002, 08:54 PM
#11
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Craig/
I have a pair of BBC's with Jesel blet drives and have not had a problem in three seasons. I also replace the belts every season.
I have a pair of BBC's with Jesel blet drives and have not had a problem in three seasons. I also replace the belts every season.
12-30-2002, 09:07 PM
#13
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Up until JDNCA1 had the belt fail I was seriously considering one for my motor. When his broke with less than 70 HRS on it my thoughts really changed. Then when he dynoed the motor and showed no HP loss I decided to spend my money on some 2 pc valve covers for easy valve lashings instead. Glad to hear there are guys having good luck with them. I know when JDNCA broke his it smacked a couple of valves and damaged the cam when the rod bolt caught a lobe. At 6000 RPM things would have been much worse than at idle. He got lucky!
Later
Later
12-30-2002, 10:01 PM
#14
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thanks for the tip wette vette. This was the last thing I was researchin.. slapping the short block later next week. UPS man is gonna be busy bringing me packages 
I am ending up with the Cloyes "true" double roller. Not to many to pick from when they have to fit the factory roller cam setup..
Travis
I am ending up with the Cloyes "true" double roller. Not to many to pick from when they have to fit the factory roller cam setup..
Travis
12-31-2002, 07:33 AM
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When I first assembled my motor I wanted to go with the Jesel but they didn't make one for a Gen 6 at that time. Plus I needed something adjustable so I went with the Hex a just which is just single roller , I was pretty concerned about this but after 80 hours that chain was in better shape than my friends double roller (which eventually broke that summer).
In retrospect I could have just redrilled some holes for a standard timing cover and ran a double roller, I sure have learned alot in the last few years!
In retrospect I could have just redrilled some holes for a standard timing cover and ran a double roller, I sure have learned alot in the last few years!
03-13-2004, 12:08 PM
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The camshaft hits a "harmonic" at certain rpms... where the springs make it jump forward in rotation... then load back. From what I understand... auto engines that are contantly going up and down through the rpm ranges "pass through" this harmonic... but boat engines that run more at a constant rpm tend to have this harmonic "chatter"... If you have ever heard a gear drive in a car or hot rod with an open engine compartment... it is a loud whine. So from what I've gathered... the valve train components are getting a shock wave sent through them when it hits this harmonic, which can cause early failure. Any other opinions?...... Funny thing... Pete Jackson Gear drives is just around the corner from where my shop is located.I've met his deceased brother "Kong Jackson" who used to make hot rod parts in the early years.
03-13-2004, 12:17 PM
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Also... due to the design of the gear drives.. the gears are straight cut. They have to be straight cut because the center gears "float". If they were cut in a helix pattern... they would tend to "side load" and walk off the other gears. Straight cut gears tend to be first off... noisy.. second .. they don't transmit the energy from one gear to another smoothly.. they slightly accelerate and then decelerate depending on the tooth engagement... that is why all modern transmission gears are helical cut. Plus on a chain or belt the force driving the cam from one gear to another is linear. The chain "pulls" the upper sprocket. Whereas the gears tend to push apart. The chain is more efficient.On DOHC engines there is always a "slider" or tensioner on the slack side of the chain... this helps to damp out any harmonics from the cams.
03-13-2004, 06:04 PM
#19
From what I have been told the harmonics is created in the crank and is transmited up to the cam.
That is why the Harmonic dampner is on the front of the crank and not the cam.
With every firing of the pistons the crank flexes and then unflexes. This motion is the harmonic.
Using a gear drive transmits that harmonic vibration to the cam.
A chain doesn't transmit it as much.
A belt drive is the best.
That is why the Harmonic dampner is on the front of the crank and not the cam.
With every firing of the pistons the crank flexes and then unflexes. This motion is the harmonic.
Using a gear drive transmits that harmonic vibration to the cam.
A chain doesn't transmit it as much.
A belt drive is the best.
03-13-2004, 06:24 PM
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Hmmm... interesting theory.... Harmonic dampers are also called vibration dampers too... I would think the vibration damper would cancel out the vibrations that would pass through the gears... some engines have gear cases that drive the cams... and they don't have vibration dampers at all... case in point... the old 750 MV Agusta motorcycles.. no cam chain to drive the cams... just a gear case with gears stacked up to turn the cams... but those cams don't have push rods and rockers and as much mass to accelerate and decelerate...interesting ... any other opinions? I can see how the chain could transmit less vibration since the force it imparts is linear... I think a lot of the vibration of a gear drive on a BBC is generated by the gears themselves... spur gears are terribly noisy on their own.
