Taller 5th in a 33/11

Discussion in 'Airheads' started by ME 109, Nov 1, 2012.

  1. ME 109

    ME 109 Long timer

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    I think plastigauge would suffer from the high temp required for fitting the cover plate?

    I've thought of calling the local bmw dealer who apparently have an airhead knowledgeable head mechanic, and asking if I can pay to get the shims measured.

    Apologies for dragging this thread out and perhaps making mountains of molehills, but I'm learning heaps.
    #61
  2. disston

    disston ShadeTreeExpert

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    I once suggested Plastigauge on another forum and was told it does not work. It's not made for this application. It is made for crank pins and rod bearings and it works there. This may not make a lot of sense but people who supposedly know say it won't work.
    #62
  3. ontic

    ontic

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    yeah, that was my thought too. I was thinking of trying to make a plait or twist of thinner soldering wire first, and try to use that to determine where your ballpark is, then see if you can get a thicker strand of solder that is just too thick. I was imagining it taking a few tries to raise (or destroy) the confidence level.
    For putty, you could try that 'knead it' epoxy stuff (often used for metal repair). It is about the consistency you want- only problem is that the couple of tubes I've owned have all set-up pretty quickly. There must be a slow cure version?
    #63
  4. ME 109

    ME 109 Long timer

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    As far as I know, the way to use plastigauge is to measure the width of the squashed plastigauge after it has been removed from the test location (big ends etc) The specific size of plastigauge used can be cross referenced with the 'squashed width' to determine clearance.
    #64
  5. ME 109

    ME 109 Long timer

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    Just had a little play with the donor cover and found that I can get 2 thou difference with the depth gauge by moderately pressing on the cover.
    Success with the solder depends on whether the solder can create as much resistance as my pushing on the cover...

    The two options I see are starting with the solder diametre as close as possible to the correct shim size, and/or use a softer solder.

    Talk about splitting hairs.
    #65
  6. mendoje

    mendoje Been here awhile

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    All of us who've used Plastiguage have probably used it to measure radial clearance for crankshaft bearings. I just found these on the Plastiguage website: http://www.plastigaugeusa.com/how.html

    "Shaft end-float lends itself to direct measurement by PLASTIGAUGE"

    "PLASTIGAUGE is particularly effective for the measurement of separation in moulding tools, and wherever it is required to determine the separation between hidden surfaces"

    So, my assumption that the calibrated measureing tape it comes with was only applicable to radial clearance wasnt so!

    I think the main issue now, is whether it will stand up under a heated part.


    #66
  7. ME 109

    ME 109 Long timer

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    Further on down the road...
    I bought a shimming plate from Cycle Works.
    It has been an interesting learning experience, this shimming business.

    I remeasured everything again this morning and have come up with the following shim requirements.



    Lay shaft needs .95 shim
    Input shaft needs .876 shim
    Output shaft needs .935 shim

    Gasket included in calculations.

    Anyone hear alarm bells?
    #67
  8. ME 109

    ME 109 Long timer

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    Even further on down the road.

    I put the cover plate back on with very close to the shim stacks noted above. All good until I got towards the last three fasteners (I called them fasteners to avoid the bolt, screw, cap screw, machine screw thingy)
    The input shaft tightened up. WTF? this, after 15,000,000 measurements.:huh

    Well off came the cover again and out came approx .02mm from each stack.
    Frustrating trying to come up with the numbers again from a choice of about 16 shims.

    Cover went back on, all buttoned up and a nice free input shaft. Minus the input seal.

    I've had a couple of rides so far and all seems well. Smooth positive shifting with no false neutrals.

    The taller 5th is a gem! The RS has plenty of power to pull with the reduced rpm.
    With a 33/11 I'm quite sure 130kph on the speedometer ran @ 5000.

    Now, 130kph is running @4500
    120 @ 4000
    100@ 3500.....used to be 3800

    That appears to be a difference of 4-500 rpm @ 130 and 300 rpm @ 100

    Bottom line, I like it.
    All my fun in the mountain twisties is 2nd 3rd and 4th so nothing lost there.

    Cross my fingers that it will do another 13 years before showing chips on the magnetic plug.
    #68