The stock pin on 91-99 engines is supported only on the outboard side of the lifter bore only. 1) 2)
As such, they don't have a lot of strength or stability and they can easily fail, .
Therefore, it doesn't have a lot of strength or stability (particularly with inadequate clearance).
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.
It is an alternative to tapping for the threaded pins. 3)
That retains the stock look with the triangular cover.
You can also have longer pins made at your local machine shop.
But you still have to drill the hole longer for the extra length pins.
But then HD one-upped them in 2000 when they came out with the screw-in pins (18532-00) as shown below. 4)
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. 5)
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. 6)
| 91-99 lifter pins vs 00-05 lifter pin screws 7) |
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