Precision is part of building any high-performance engine — not checking measurements on parts and how they interact with each other during a build is asking for trouble. One area that might not get checked enough is the lifter-bore clearance. Erson Cams addresses why this is an important thing to check in this video hosted by Jeff Huneycutt.
If someone is building an engine for the first time, they might make the mistake and assume the lifters will drop right in and work. This isn’t the case, because aftermarket blocks will have different machining tolerances from the manufacturer, and with a used block, you don’t know what the previous builder spec’d the lifter bores to be. Either too much or too little clearance is very bad for any type of lifter, so checking the bores needs to be a priority before you begin assembly.
If you’re building an engine that uses flat-tappet lifters, you’ll need to keep in mind the lifters need to have much tighter bore tolerances than a roller lifter. The largest you’ll want to go is between .0013- and .0019-inch. A roller lifter has more room to work and can operate with tolerances of .002- to .003-inch.
Why is this so important? If the bore for a flat-tappet lifter is too large, it allows it to “wiggle” too much, and the lifter has to rotate on the cam inside the bore. When the lifter bore has too much clearance, it will allow the flat-tappet lifter to rock on the cam lobe. This will cause lubrication issues, and will ultimately lead to some type of failure.
Since a roller lifter has a roller wheel on the tip, following the cam, any additional movement isn’t an issue. The roller wheel can take up the slack, allowing the lifter to follow the camshaft profile as it’s designed. This means there won’t be any lubrication issues that could damage the cam or lifter.
If you aren’t sure what kind of machine work has been done to an engine block you’re working with, you’ll want to check the lifter bores. The process is fairly straightforward, but it does require precision measuring devices. By checking the lifter bores before you assemble an engine, you will avoid the possibility of a lifter failure.
Make sure you check out this video from Erson Cams where Jeff Huneycutt shows you how to find the lifter bore clearance.