Crankshaft Sprocket: Replace or don't replace?

[Hector]

who didn't know the difference between a ball point hammer and a claw hammer. Some are just book smart but have no common sense for stuff in everyday life.

About your experiment of measuring the expansion of a material, you can probably do this yourself with Al. Al has a CTE of 24 microns/m C which is one of those materials that loves to expand/contract. Just stick an Al ring in the freezer measure ring DIA w/ ruler in mm, then heat it up to 100 C and measure ring DIA with ruler again. You should see the difference, and should measure a difference of about 2 mm for the ID from 0 to 100 C.

[Hector]

you'll measure about .2 mm (about 8 mils) so you'll probably need a caliper for the measurements.

who didn't know the difference between a ball point hammer and a claw hammer. Some are just book smart but have no common sense for stuff in everyday life.

About your experiment of measuring the expansion of a material, you can probably do this yourself with Al. Al has a CTE of 24 microns/m C which is one of those materials that loves to expand/contract. Just stick an Al ring in the freezer measure ring DIA w/ ruler in mm, then heat it up to 100 C and measure ring DIA with ruler again. You should see the difference, and should measure a difference of about 2 mm for the ID from 0 to 100 C.

[Unregistered]

Well, both Tom & Ray attended MIT, but I was mistaken about their degrees, which apparently did not include physics, per Google info. I have emailed my question to their Car Talk website, and hope they answer me from among thousands of questions. We'll see.

My recent empirical experience with pressing a bearing on an alternator shaft demonstrated that freezing works--it went on faily easily, despite difficulty during room-temperature attempts.

Using keywords "steel thermal expansion" on Google found various interesting websites, with info about thermal coefficients of expansion of various materials. For example, one noted that a copper disk with a hole in the middle (sorta like an old music short-play 33 rpm vinyl record or a modern CD) would enlarge the hole when the disk is heated. That jibes with what others are saying here on Bimmer.info. Granted, steel, copper, and everything else have different thermal expansion properties/coefficients, but presumably behave in essentially the same way, albeit at different rates.

Remember when the Challenger space shuttle blew up? That was due to thermal contraction from over-chilling of a large (admittedly rubber) O-ring. The O-ring material got skinnier and its sealing function failed, letting hot gas blow past. The rest is sad history.

It seems conceivable that both heating AND chilling may work to enlarge the doughnut hole. Heating by virtue of making the entire piece grow, pulling the inner diameter outwards in the process, thereby increasing ID. Chilling by reducing the gap between molecules, causing the inner and outer surfaces & diameters to converge slightly, also increasing ID.

Curious, I'm gonna get my kid to work this problem in his HS physics and metals classes--heated, chilled, and ambient measurments of a used bearing ring. Before & after measurments in each temp. scenario. However, the teachers/kids are busy at school's year-end, so this may take awhile.