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Salvaging Or Correcting Lifter Bore Geometry
By Doc Frohmader
When I first started playing with engines, if you had a defective or damaged lifter bore there wasn’t
anything practical to do about it but find another block. I hate to admit this because it’s yet another indication that I’ve become an old guy (as hard as it may be to believe, I was born pre-small block-Chevy or PSC). Even today a great many blocks are scrapped if the lifter bores are worn or damaged.
So what do you do if you have a rare or expensive block and don’t really want to scrap it? Lifter bushings. Bronze bushings that are installed in oversized lifter bores and reamed to size.
Even for those blocks where the stock lifter bores are still in reasonable shape, bushing lifter bores may not be a bad idea. The
precise alignment of the main bores, camshaft bores and lifter bores is essential to peak performance. Alter it by changing the lifter bore angle relative to the cam lobe and you will no longer have correct geometry. The lifter may not rotate or may rotate too much. You may end up with the lifter edge-cutting into the cam or vice-versa. In any event, the cam and lifters will not live as long as they should.
In another scenario, the lifter bores will not be located at the correct angle relative to the cam lobe. This will alter cam timing. Granted, if all your lifter bores are at the same incorrect angle, you
can adjust the cam timing to accommodate most of the problem, but then you have to KNOW exactly what the problem is and how to fix it.
In reality, when lifter bores are measured, they are typically staggered and not consistent at all. So what are you going to do, have the cam ground to match each defective lifter bore angle? I doubt it.
Of course, the most obvious defect in lifter bores is excess clearances or other damage. Remember that oiling in an engine is a matter of a series of controlled leaks. The clearance between the lifter and lifter bore allows oil to pass and keeps the lifters lubed
and cooled. If you have too little clearance, the lifters can stick or wear prematurely. If you have too much clearance, you can lose oil pressure and/or create a situation where the lifter no longer travels
smoothly, but rocks and bounces. Quite obviously, correct and consistent clearances are critical to peak performance.
By installing lifter bushings and machining them to blueprint specs, you can eliminate all of these issues at once. The key to this procedure is a fixture setup from BHJ that uses existing cam and crank centerlines to exactly position and guide the process of over-boring
and aligning the new bushings. This is a precision set of tools which,
for obvious reasons, are not toys and are not swap-meet cheap. Granted, most machine shops will have parts of the fixture (used for other machine operations), but to fully equip from ground zero and have all the correct cutters, reamers, adapters, etc. for the BB Chevy like that shown in this article, you’ll have to spend over $1,800.
Oh, and you’ll need a mill. That’s not exactly cheap. Now, to set up to install lifter bushings in a second type of engine, say a SB Chevy, you’ll only have to add another $450-$500, so adding capacity is a lot less than the initial outlay, but you can see that this is professional stuff. You can also understand why the typical lifter bushing job runs
in the $350 to $400 range. I can tell you from experience it also takes a lot of careful work and patient setup to complete.
The block that Jim Badgley of Overland, MO’s Dependable Machine and I worked with was an otherwise nice factory 454 block and there had been no problem with sloppy bores or other damage. However, as soon as the fixtures were in place, it became obvious that the original bores were not exactly perfect. BHJ includes a setup tool used to check alignment of the lifter bores. In some cases the tool dropped right in. In others it would drag. Still other bores were as far as .030˝ shifted and the tool was never going to
pass through. What this tells me is the OEM machine work left a lot to be desired. The new bores would be a significant improvement over the originals.
This block did not have a lot of core shift evident. One thing performance people always look for is core shift because it can cause a lot of problems such as thin spots in cylinder walls. However, when it came time to machine out the oversized bores the new bushings fit into, core shift was really obvious. Again it was not excessive, but this kind of operation tells you a lot and keeps you thinking about the relationship between quality castings and good machine work.
So if people aren’t likely to do it themselves unless they work in a machine shop, why would they want to know more about how it’s done? Well, first, you’ll probably have to explain why it’s not a $50 job. The bushings cost that much. Besides, this job takes several hours of concentrated machine shop time and no one works for free. And of course you know the cost of the equipment. I see it as a fair expense for serious machine work.
Finally, and most important, when you see how the work is done, you will also be able to understand clearly why this operation is valuable to your performance interests. Somehow, in the elegance of the tooling, the essential dimensions and geometry sort themselves out.
I hope it will become clear that lifter bores have to be located on centerlines in two different dimensions (inside/outside and front/rear). I think you’ll see how the correct angle of the bores relative to the crank and cam centerlines is critical. And (if you don’t already understand) you’ll know how correct clearance and smooth operation due to correctly sized and finished bores will improve the performance and durability of your engine project.