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455 cam button?


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I shop I know has a 455-powered GS customer car and they're doing some work on it.

The engine was rebuilt by someone else, and when they went to fire the car up the day the owner was supposed to come and get it, they found that the cam gear teeth on the new MSD distributor were broken and the cam wouldn't turn, though they had driven around the parking lot and to the muffler shop and alignment shop earlier.

To make a short story long, they pulled and tore down the entire engine, and besides finding a deeply scored crank and trashed bearings, the wear pattern on the cam lobes has an "S" shape to it, like the cam was walking forward and back in the block while the engine was running.

Do 455s have a cam thrust bushing that the engine builder decided was a spare part?

Thanks

-Brad

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Okay, anybody have an idea what would cause the cam to walk forward and back in the block?

It's more than improper break in--the wear pattern on the lobes was off the face of the lobe as the lifter goeas around the base circle, then as it rises on the lobe the lifter's wear pattern moves into the center of the lobe and rolls over the cam lobe centered, then it migrates back to the edges and "falls off" the lobe. You can see that at one point on every lobe, the lifter isn't riding in the center of the lobe, but way off to the side.

It looks like the camshaft is moving toward the timing chain cover about 3/8-inch and then back toward the back of the block, in the position it should be when installed properly. The teeth on the cam gear are broken off at the end, like the cam was slid forward when they broke off.

They also had a problem with the oil pump losing its prime. Related?

Thanks,

-Brad

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