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Old 11-16-2009, 10:44 AM
BogiesAnnex1 BogiesAnnex1 is offline
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Originally Posted by Biscuit6447
Good info. I am not using this motor as an oval track only, but definiatley want a good oil system. I just put the crank in, and from a plastigage, i got a little over .002. the thrust bearing was a little more than the mains. the mains show closer to .002 that .003. ~.0023ish i would imagine.

Is the melling hv oil pump (#m55hv) good? i had it in my last motor, but some say that it was partly the cause of my stretched timing chain.
The Melling is fine, just disassemble it and inspect it for cleanliness and clearances. Make sure the relief valve works smoothly and the passages don't have burrs.

The timing chain has little to do with the oil pump beyond spinning the cam to drive it. That said, the power it takes to drive an oil pump isn't anything compared to the dynamic vibration moments the valve train introduces into the camshaft. The cam is constantly snapping forward and backward against the gear and chain interface. The same interface also sees similar action at and from the crankshaft.

Every time a lobe raises a lifter the cam's rotation is slowed. On the opposite side of the lobe, when the lifter goes over the top of the lobe the spring closing the valve adds an acceleration to the cam. For a race engine with powerful valve springs, this gets to be considerable moments that try to alter the speed of the cam. This rattles the connection of the chain inside the gear tooth mesh with a lot of force and at high frequency.

On the other end of the timing chain, the crankshaft slows somewhat every time it has to push a piston to compression and to a lessor extent to exhaust, then it is greatly accelerated on the power stroke. So while the crankshaft is turning a constant RPM it is being subjected to all these slowing and accelerating moments to which it cannot respond with a speed change. These moments set up a twist in the shaft such that it is constantly winding and unwinding. Granted the amount of movement is small, but it does set up a considerable vibration inside the crank. The nose end takes the biggest beating as the drive end has a flywheel/clutch or torque converter to soak up the vibrations. On the front end you've got a damper whose job it is to absorb vibrations getting to that end of the crank. However, the timing drive gear and cam drive chain are between the throws and the damper, so the driving gear sees those vibrations and introduces them into the chain thru the tooth to chain engagement. So especially, the timing chain in this system takes a considerable beating. In a grocery getter street engine with this set up, the life span is pretty decent but as the the engine gyrates toward increasing levels of performance, the life span begins to take a reduction to where in race engine it's a beating. Gear drives are an attempt to overcome the lifespan and timing accuracy deficiencies of the chain and gear set up, but this is a brute force solution which has it's own set of problems especially at lower RPMs.

You'd be surprised at how many race engine builders use the factory type silent link chain with either nylon toothed or steel gears. The reason is that these tend to isolate the crank vibrations from those of the cam which results in better distributor timing stability where a crank trigger ignition is rules prohibited. But this is a set up that is short lived, but while it's on it's really good. Roller chain is something of a compromise as it absorbs some of the vibrations but not as well as Morse chain, while the roller is more resistant to stretch and wear in the gear teeth than the Morse, so it tends to last longer than OEM style chains. Gear drives, I think, are better suited to engines that see a lot of time at constant or nearly constant high RPM. Getting them out of the slower speeds lets them overrun the oscillating moments on the cam and crank so they pick up a lot of stability. At lower or constantly changing RPMs they tend to telegraph vibratory moments into the cam making holding steady timing at the distributor difficult and subjecting the gears to a beating they really don't need. The stronger gears just move the vibration problem into the crank and cam. So if your racing is a type where you put the pedal to metal and aim the car, a gear drive could be a good way to go.

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