GO FISHING, use SLABSAUCE Fishing Attractant
Page 3 of 3 FirstFirst 123
Results 21 to 27 of 27

Thread: Crankshaft Sprocket: Replace or don't replace?

  1. #21
    Join Date
    Jan 2004
    Posts
    4,150

    Default If you check you'll see that both click and clack had degrees from

    mit..... One had a degree in economics and the other had a degree in humanities... No physics degrees though.... A ring when cooled shrinks ID and OD...





    Quote Originally Posted by Unregistered
    OK, lemme get this straight:

    1.) A ring, when cooled will shrink in onto itself, making the inside diameter larger, so it will slide more easily onto a shaft of given outside diameter.

    2.) A sprocket is a ring.

    3.) Nevertheless, heating the sprocket works best, in spite of what item 1 says.

    Seems to me, upon chilling, the ring (or anything but water, which expands on freezing, unlike 'most everything else in the world) would contract in onto itself, so its inside diameter would be larger, and its outside diameter would be smaller. The constituent molecules are clueless as to inside, outside, up or down: They just contract into a smaller space. This is essentially what Tom and Ray (the Tappet Bros. on Sat. morning NPR's "Car Talk" show) say. Tom or Ray has a master's degree in physics from MIT and they run a car fixit shop, so they seem like a creditable source.

    As this is an extremely handy thing to know, can somebody please micrometer-measure a sprocket, ring (or whatever) at room temp, at heated temp, and at freezing temp, and tell us all the difference(s)?

  2. #22
    Join Date
    Jan 2004
    Posts
    1,235

    Default

    Check out this link: http://www.newton.dep.anl.gov/askasc...0/phy00741.htm

    BTW: I also have a Master's Degree from MIT. In Mechanical Engineering though, not Economics..
    Last edited by Robin-535im; 05-18-2004 at 02:09 PM.
    Robin

    72 Chevy K10
    01 E39 M5

  3. #23
    Join Date
    Feb 2004
    Posts
    558

    Default I knew a guy from an Ivy league school...

    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.

  4. #24
    Join Date
    Feb 2004
    Posts
    558

    Default Correction. If you have a piece of Al with a 10 cm ID

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

    Quote Originally Posted by 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.

  5. #25
    Join Date
    Jan 2004
    Posts
    1,171

    Default

    As Bill says, a ring when cooled shrinks I.D. and O.D. and conversely when heated expands I.D. and O.D. The best way to rationalize why a ring I.D. shrinks versus grows when cooled is...visualize a single chain of atoms around the I.D. of the ring...a diametral chain only one atom thick. When cooled, the distance between the atoms becomes less reducing the I.D./length of the chain comprising the hole. Conversely, when heated, the distance grows increasing the I.D. of the hole. The O.D. of the sprocket is a bit more intuitive but the same principle applies.
    On that note, I haven't seen any good porn on this site in a long time. Someone help me out.
    George

  6. #26
    Unregistered Guest

    Default

    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.

  7. #27
    Join Date
    Dec 2003
    Location
    Eastern Tennessee USi
    Posts
    14,839

    Default

    porn is a good thing!

    (_o_) (_o_)
    95 E34 530I V2.37
    ===========
    Those who make peaceful revolution impossible will make violent revolution inevitable.

    John F. Kennedy

Page 3 of 3 FirstFirst 123

Similar Threads

  1. How to replace a windshield?
    By zhandax in forum 5 Series BMW
    Replies: 10
    Last Post: 05-28-2009, 06:09 AM
  2. Anybody replace their idler arm?
    By Russell in forum 5 Series BMW
    Replies: 1
    Last Post: 03-11-2007, 10:02 AM
  3. If good replace anyway?
    By Jehu in forum 5 Series BMW
    Replies: 24
    Last Post: 01-24-2007, 07:52 PM
  4. Radiator Cap - Replace? Need to know soon, Thx!
    By zuzuk212 in forum 5 Series BMW
    Replies: 7
    Last Post: 12-30-2005, 06:29 AM
  5. gut the cat/replace the cat
    By Unregistered in forum 5 Series BMW
    Replies: 13
    Last Post: 04-28-2004, 07:21 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •