Lifter Bore Measurements

I never paid attention to this before, but with the oil pressure issues reported on this forum, I begun wondering how much lifter bore wear is a factor, that folks are just not aware of. So I measured a 273 block here; this is an approximate 100k mi engine, original, with cylinder bore wear no more than .003-.004" worst case, and no bad bearings and crank wear under .001", so this engine is a pretty 'limited' wear engine of its day IMHO. Info on the tools used, etc, is at the end of this post.

I set the gauge to the max limit lifter bore on the '65 FSM, which is .9058". All lifter bores were less than this dimension horizontally; but all of them were at or above this dimension vertically. I suppose that is to be expected with the lifter to pushrod angle putting force and wear on the bottom of the lifter bore.

I then set the gauge to larger and large sizes, and finally found the largest lifter bores. They were 4E, 1I, 7I, and 7E,and they were .9061-.9062" max in the vertical direction. The wear seemed to be more at the top than the bottom but I did not really get into that matter in detail.

As a reference to unworn bores: We were blessed with a virgin block with the last build and the lifter bores were all under .9048" or thereabouts. Assuming the bores were consistent over time (1968 to 1970 blocks dates), then this 273 looks to be worn up to .0013-.0014" in the lifter bores.

Per the FSM, the lifters are supposed to be .9040-.9045" diameter. The range of clearance is supposed to be .0005-.0015". So with these mildly worn 273 bores, the clearance with factory spec lifters could vary from about .0012" to as much as .0022", along the vertical direction.

I've measured one set of new Crane lifters (hydraulics) and they ranged from .9040" to as much as .9052". The largest 3 were .9046, .9048, and .9052". So these new lifters can range up past the FSM spec size. Crane was good enough to supply 3 new lifters .9045" and under to replace these large ones, for no charge. (We bought direct from them so they said 'no problemo' to doing this; that is an advantage to going direct to a cam maker.)

Interestingly, according to this '65 FSM, oversize lifters were available in .001", .008" and .030" sizes.. I never knew that! Going to the 2 larger oversizes calls for reaming the bores out. I'll go direct to a cam mfr for this 273 block and ask if they can sort the lifters to be on the large end of production to take up this wear. It'll be interesting to see if they will be willing to do so.

Measurement info: Measurements were made with a telescope gauge set with a .0001" micrometer (vernier scale). I don't have a reference for making sure the micrometer is dead nuts on, but it seems to check right on known parts (like new lifters). (Yes, a 1" reference is on my list!) I have used telescope gauges for 35 years; they are tricky and slow to use, but if you work slowly and carefully and pay attention to their angles and centering in the bores, I've found that you can approach .0001" tolerance. You have to be easy with them and work them back and forth a lot to get good results, and be ready to re-check them, but they will frustrate you, or fool you if you use them casually. And my dimensions could be off .0001" due to temp changes; the tools started at room temp but the garage is at 40F; I tried to keep the tools warm but eventually they cooled a bit.