Cam PlayIf you have your distributor depth set correctly and still notice undue gear wear, it could be because your camshaft is "walking" inside the block. A better term for this is "camshaft runout." It happens when the cam moves back and forth, from front to back, in the block. Davis says camshaft runout is most common when using a lightweight stamped steel timing cover that will flex and not hold the cam in place. When this happens, it sends a shock wave through the gears and up the distributor shaft and can disrupt engine timing. Signs that this is happening in your engine will be excessive wear on one side of the distributor gear, excessive play in the distributor shaft from worn bushings, and possibly damage to the cam. Fortunately, the remedy for this problem is also simple. Davis recommends investing in a sturdy machined timing cover and using a cam button to precisely locate the cam's position in the block and hold it there.

Advance WarningsDavis also cautions about ignoring the mechanical advance mechanism in your distributor. Performance Distributors customizes the advance curve in every distributor for the specific engine that it will be going into, and it is usually correct, right out of the box. But the system of weights and springs that make up the advance mechanism can wear and cause timing problems, so they do require periodic attention.

One area that is prone to wear that you might not expect at first is the top plate, where the pins serve as hinges for the advance weights. The movement of the weights can wear the pins over time and cause the advance curve to change. Davis says the chance for pin wear increases if the effects of camshaft runout is sending shock waves up the distributor.

The easiest and often most practical way to determine if your distributor is suffering from wear or other problems is simply to put a timing light on your balancer. If you check your engine's timing and notice it is erratic or changes shortly after you set it, then there is definitely a problem somewhere that must be fixed. You should first check for wear at the mechanical advance pins, the distributor gear, and the distributor shaft bushings. You will be surprised by how quickly you can spot problems and pinpoint the specific source of those problems with the right information.

Not all of the great tips for reducing distributor gear wear come from the distributor manufacturers. Crane Cams also offered this tip for improving the lubrication between the camshaft and distributor gears on Chevrolet engines. As we mentioned earlier, the only oiling for the gears in stock engine trim comes from what's splashing around inside the block. But Crane has come up with a simple way to provide the gears a fine jet of pressurized oil.

According to Crane: ". . . the bottom of a Chevrolet distributor housing can be modified to spray pressurized oil onto the distributor drive gear. The extra lubrication will reduce distributor gear and camshaft gear wear. This is especially important when the gear is used to drive non-standard accessories, such as a high-volume oil pump or a magneto that puts additional loads on it and the cam. Simply file a small vertical groove 0.030 inch wide by 0.030 inch deep on the bottom machined band (immediately above the gear). This can be accomplished by using the side edge of a file. Pressurized oil running between the two bands will be directed downward onto both the gear and the cam."

This idea sounds like a great one because it is simple, easy, won't cause much pressure loss in the rest of the engine, and will work with both iron and bronze gears.

It is possible to determine correct distributor depth with nothing more than a set of shims and a steady hand, but if you want to be a little more precise or build several engines a year, this will be useful to you. Goodson, a top supplier of engine building tools, recently began offering a tool designed to measure correct distributor gear depth.

Known simply as a distributor depth gauge (PN DDG-05), this tool allows you to precisely measure the distance from the distributor seating flange on the intake to the oil pump driveshaft and then match the measurement to your distributor. The design is elegantly simple and, in our experience, works quite well.

SOURCE
Crane Cams
530 Fentress Blvd.
Daytona Beach
FL  32114
3-86/-252-1151
N/A
www.cranecams.com
Performance Distributors
Memphis
TN
9-01/-396-5783
performancedistributors.com
Goodson
www.goodson.com