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Measure Bearing Clearance - What's Your Problem?

All About Timing
Blaine Kuhn, Fremont, CA: I have a '71 small-block Chevy 400. The engine is pretty stock: Edelbrock intake and four-barrel carb. The timing chain needed replacing so I stuck in an Edelbrock timing gear and opted to use the 2-degree-advance feature. Now with no carb changes other than idle speed, the car has zero torque and it takes two-thirds-throttle to get the thing moving. But once it hits about 2,500 rpm, it has much more get-up-and-go. Any help would be really nice, even if I'm not going to like hearing I have to tear it down again and put it to retarded or stock...argh.

Jeff Smith: We're not always the bearers of good tidings, Blaine. It sounds like when you installed the timing set, the marks between the crank and cam gears were not precisely aligned. This places the camshaft one tooth off, which can either be advanced or retarded. The amount the cam timing is off depends on the number of teeth on the cam gear. For example, I think the Edelbrock gear for the small-block Chevy has 44 teeth, while the crank gear has 22, which means the cam spins at half crankshaft speed. If we divide 360 degrees in a circle by 44, we get 8.18 degrees. If the cam gear had 40 teeth, then one tooth would be equal to 9 degrees. That is why adjustable cam gears rarely offer more than 8 degrees of retard or advance. If you needed more than 8 degrees (and why would you?), just move the cam gear one tooth.

You mentioned your engine is very sluggish until about 2,500 rpm. With all other things like ignition timing and carburetion set properly, your description sounds like you accidentally retarded the cam gear by one tooth, which would retard the cam timing by roughly 9 degrees and easily make your engine run the way you described. You will have to remove the water pump, harmonic balancer, and timing cover again, which also means loosening and dropping the oil pan-a real pain on the original small-block Chevys. This might be a good time to consider a one-piece oil pan gasket (sold by Fel-Pro). That could save you a lot of grief.

Before you remove the cam gear, remove all the spark plugs and slowly turn the engine over until the little mark on the cam gear is at its lowest point. For the cam to be timed properly, the dot on the cam gear should line up perfectly with the dot on the tooth on the crank gear (as in our photo of a small-block Chevy cam installation). More than likely, your cam gear dot is not lined up with the crank gear and is retarded by one tooth.

Of course, the best way to double-check your work is to degree the camshaft. If the numbers are off by 9 degrees or more, then you know you have a problem. For the record, aligning the dots does not constitute degreeing the camshaft. That term is often misused. To degree the cam requires special tools and a little bit more effort. Finally, if it's any consolation, it's an easy thing to miss the alignment of these dots when the engine is in the car. I've done it.

More Info
Edelbrock
Torrance, CA
310/781-2222
edelbrock.com

Proform
Roseville, MI
800/521-1005
proformparts.com

CC Quickies
At the same all-GM show, we ran across this absolutely gorgeous Pontiac Bonneville convertible with a Tri-power 421ci motor and couldn't resist it. This just oozes cool.

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