In a nutshell, the stock pin (on 91-99 engines) is supported only on the outboard half. 1)
Therefore it's not very strong, and it doesn't take much contact (from the lifter) to cause a failure.
By drilling the hole deeper and using a longer pin, you gain support for the pin on both sides of the lifter bore, inboard and outboard.
Zipper's has a long pin kit that came out in the 90's.
But then HD one-upped them in 2000 when they came out with the screw-in pins (18532-00) as shown below.
Not only is it longer to provide better support like the Zippers solution, but the outboard side is positively locked in place via the threads.
The main thing with installing either style upgrade is to drill the hole straight. If you're off even slightly, the tappet pin may try to bind the lifter. 2)
It can be done with a hand drill on an assembled motor if you're careful, but it's best done in a drill press or a mill with the right case half removed.
Basically you just punch the hole deeper with a 3/16“ drill bit, drill the outer portion only with a .201” bit and tap it to 1/4-20“ threads.
Put tape on each drill bit so you know where to stop.
Anti-roll pins are designed to keep roller lifters from turning sideways during operation.
A roller that's turned sideways does not roll. 3)
| 91-99 lifter pins vs 00-05 lifter pin screws 4) |
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