![]() ![]() Too many shims, however, may push the base of the button past the gear face and not allow the cam bolts to seat fully against the cam gear. We’ve found it’s easier to add length to the button by placing shims behind the button. Stock timing covers do not offer this kind of convenience so the engine builder is forced to be innovative. This makes measuring endplay really easy. The hole lines up with a portion of the cam gear. Aftermarket aluminum timing covers usually come with an access hole that is covered with an Allen plug. A nylon button that is too long is much easier to remedy since that requires only sanding or filing the backside of the button until the proper length is achieved.Īnother issue that comes up is properly measuring cam endplay. In one case, we needed at least 0.010-inch of shim thickness, and cut up an aluminum soda can to make three shims that measured a combined total of 0.012 inch. For example, we’ve often had to make shims to fit behind the button in order to create the proper clearance. Getting to the Thousandth of an Inchīecause of variations in the thickness of the timing cover gasket and position of the timing chain cover, you can expect that this will require some effort to custom match the buttons to each specific engine. Secondly there’s a convenient hole in the cover to check camshaft endplay. First, the top portion of the cover can be quickly and easily removed without disturbing the oil pan and seal. It’s a matter of preference between the nylon buttons and the more expensive roller bearing buttons.Īfter installing the button in the gear, these Comp two-piece aluminum covers are nice for several reasons. (Right) The button fits inside the cam gear center hole and will then contact the inside of the timing cover to prevent the cam from moving forward. We prefer the roller buttons since they don’t wear during use, but the nylons are nice because if they are a bit too long, they are easily shortened by filing the flat, cam-side of the button. (Left) We’ve laid out several lengths and style of buttons in this photo. As an example, the ’86 and later small-block Chevrolet and the Gen-II LT1 engines that followed were equipped with a steel limiting plate that required the use of a stepped nose camshaft. We’ve never actually tested the negative results, but it is possible to see 20 degrees of retarded timing at higher engine speeds from a roller cam with no button or thrust plate.Īll of this points to why, when early engines were converted to roller valvetrains, the factory equipped the block with a limiting plate. Cam walk of more than 0.010 inch induces retarding of the ignition timing. When the cam thrusts forward, it also counter-rotates the distributor gear, retarding the timing. This forward movement of the cam in the block is to be avoided because once the cam begins to move, this also affects the relationship of the distributor gear to the cam gear. If left unrestrained, the cam will walk forward, which will twist the distributor gear and retard the ignition timing. Both hydraulic and solid roller cams require some type of device to prevent the cam from moving forward during engine operation.
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