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Thread: MC crankshaft alignment and balance tool.

  1. #1
    [email protected] tonyfoale's Avatar
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    MC crankshaft alignment and balance tool.

    In my recent post about fly cutters at A double edged fly cutter. I showed a photo of the fly cutter being checked for balance on a tool that I had made. I thought that I had posted that tool on this forum previously but when I searched I couldn't find it. Aging memory problem. I had posted it on some motorcycle Facebook forums.
    To avoid rewriting it just for this tool forum I present just as it was elsewhere. Although made for a specific type of crankshaft I have used this tool for balancing many other things, as for example the fly cutter.

    Background.

    I have never liked the usual crank alignment methods of either supporting the crank between centres or on V-blocks. A problem that I have always seen is that it is sometimes difficult to interpret exactly what the measurements mean. Regardless of the method used the alignment tolerances are usually quoted as the same but what you measure depends so much on the length of the shafts if between centres and the mounting position if on V-blocks.

    I have often avoided these problems by mounting a single mainshaft in two bearings such that the crankshaft as a whole rotates about the axis of that mainshaft. Then any misalignment measured on the second mainshaft is a clear indication of what is wrong. However, for this method to have validity the main shaft must be a good fit in the supporting bearings with no play and this makes crank alignment rather slow because it takes too long to push the mainshaft into the bearings before checking and then removing it prior to attacking it with a lead or copper hammer to correct any misalignment.

    For several years I have been intending to make a tool to enable me to locate a mainshaft without play but which was rapid to mount and dismount the crankshaft, but the task never bubbled up to the top of the pile of things to do now. That is until recently. For reasons of expediency I was trying to align an Aermacchi crank shaft between centres but nothing made sense. Runout measurements seemed incompatible. In desperation I made up a bearing holder to support the crank by a single mainshaft. Then the problem became quickly apparent, the other mainshaft was bent at the reduced diameter where the alternator attaches. I am guessing that sometime in its past it was dropped and landed on that shaft. The bearing mount part of the shaft was not bent and it was easy enough to get that aligned with the other shaft, and then it was clear that the runout at the alternator end of the shaft was close to 1mm. Of course that meant that the centre on that end of the shaft was out by the same amount, leading to the original alignment problems. This told me that it was time to make my long planned tool.


    Implementation.

    The idea is quite simple, I would mount two ball bearings close to one another to support and allow rotation of the bearing area of one mainshaft, similar in concept to that of static wheel balancing fixtures. However, the overhanging weight of the crankshaft requires an additional support force acting downward at the other end of that mainshaft. To handle that another pair of bearings is to be mounted above the end of the mainshaft. Now that mainshaft is forced to rotate about an axis through the centres of the supported journals. Insertion and removal of the crankshaft into the tool is simplicity itself and very fast. Measurements of runout on the other mainshaft give easy to interpret indications of the remedial actions needed to correct any errors.

    This tool also seemed to be a good base to use for crankshaft balance factor determination and correction. However, good sensitivity for balance measurement requires the lowest possible friction in the bearings. Although regular unsealed steel ball bearings lubricated with very thin oil would probably work well enough for practical purposes, I choose to use modern ceramic bearings which have very low friction when run dry, as long as they are kept free of dust and dirt.

    Although the tool featured here has been made as Aermacchi specific, it could just as easily be made to suit any other crankshaft. With a little more work the bearing mounting could be made adjustable for those who have need to use it for a range of crankshafts.

    Click on the following pix. to see them full size.

    MC crankshaft alignment and balance tool.-balance01.jpg MC crankshaft alignment and balance tool.-balance02.jpg
    The solid framework was constructed from material lying around the workshop. The base is from the saddle of an old lathe and the two bearing mounting blocks were from some old tooling fixtures. Note the white colour of the ceramic bearings.

    MC crankshaft alignment and balance tool.-balance03.jpg MC crankshaft alignment and balance tool.-balance07.jpg
    Shaft fitted to demonstrate how the bearings work to provide support. The extra holes and cutouts in the blocks are just a legacy of their previous life.

    MC crankshaft alignment and balance tool.-balance05.jpg
    Crankshaft mounted in the tool for checking alignment. Runout can be checked at both extremities of the shaft and also on the flywheel face to check for parallelism between the two wheels.

    MC crankshaft alignment and balance tool.-balance0.jpg
    Crankshaft mounted for checking balance factor. The ease of mounting the crankshaft is clearly apparent.

    MC crankshaft alignment and balance tool.-balance04a.jpg
    Crankshaft mounted for checking balance factor. The ceramic bearings give a very high degree of sensitivity.

  2. The Following 10 Users Say Thank You to tonyfoale For This Useful Post:

    Carlos B (10-11-2017), DIYer (10-11-2017), Kevic (08-02-2018), olderdan (10-10-2017), Paul Jones (10-14-2017), rendoman (10-12-2017), Seedtick (10-10-2017), thevillageinn (10-23-2017), UncleBob (07-20-2018), VegeKev (03-21-2018)

  3. #2
    olderdan's Avatar
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    Tony, this is a great idea and typical of your way of thinking, In the past I have tried using the lathe centres but just like a conventional jig it would tell me something is wrong but not where the problem is.
    I am assuming the crank has to be mounted horizontally to get a good result, especially for balancing, so would a universal one would need a height adjuster built in at one end.
    BTW is that balancing pic a demo or would you normally have the piston assy in place.

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    tonyfoale (10-10-2017)

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    Tony, i think your an advocate of KISS.
    I to never liked setting cranks between centres, i always liked to get as close to the actual flywheels as possible with knife edge vees and slide the dial gauge indicator along the shaft. I always checked the shafts for bend by rotating the shaft and checking at 12,3,6 and 9oclock. I started at close as possible to the crank web, the middle and then the end.
    This was a method i had evolved after a lot of hassle with a crank that would not read true no matter what i did. Like you i traced it to a bent shaft after a lot of head scratching and wasted time.
    I rarely do cranks now except for myself and a few friends however i think i will use your idea and use two vee knife edges hardened instead of the ceramic bearings. Cost factor here as I'm supposed to be retired. I would, however, make the rear assembly on a sliding carriage to facilitate different length shafts.

    Well done on this idea and keep them coming, please.

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    tonyfoale (10-10-2017)

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    [email protected] tonyfoale's Avatar
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    Quote Originally Posted by olderdan View Post
    I am assuming the crank has to be mounted horizontally to get a good result, especially for balancing, so would a universal one would need a height adjuster built in at one end.
    BTW is that balancing pic a demo or would you normally have the piston assy in place.
    Actually mounting the shaft horizontally is not a prime requirement but it is desirable to be reasonably close. So an adjustable height would be useful.
    For balancing a single cylinder machine you normally balance to a certain percentage of the reciprocating mass, a piston would be too heavy so I make up an appropriate mass out of pieces of metal and nuts etc.
    Here is a magazine article on balancing that I wrote ages ago
    https://www.dropbox.com/s/hxx4u3kvq3...ssage.pdf?dl=0

    Here is another on DIY balance
    https://www.dropbox.com/s/jhtcgq4zy6...lance.pdf?dl=0

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    EnginePaul (03-21-2018)

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    [email protected] tonyfoale's Avatar
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    Quote Originally Posted by Fast Fergie View Post
    Tony, i think your an advocate of KISS.
    I am a dedicated devotee of KISS,

    Quote Originally Posted by Fast Fergie View Post
    I rarely do cranks now except for myself and a few friends however i think i will use your idea and use two vee knife edges hardened instead of the ceramic bearings. Cost factor here as I'm supposed to be retired. I would, however, make the rear assembly on a sliding carriage to facilitate different length shafts.
    I am supposed to be retired also but I can't turn work down when an interesting consulting proposition comes along. I am too old to have other vices so my cash is all directed toward racing and fine vino, but most of my tools and gadgets cost very little. Adjustable height at the rear like olderdan suggested and a sliding carriage as you mention would make the device universal but as you noted I am into KISS and I built this for a specific type of crank.

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    [email protected] tonyfoale's Avatar
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    I should have mentioned that if you go to the "Freeware section" on my web page www.tonyfoale,com you can download some software which allows you to play with balance factors etc. click on "Engine balance-factor analysis" to download it.

  11. #7
    Content Editor DIYer's Avatar
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    Thanks tonyfoale! We've added your Crankshaft Balancing and Alignment Tool to our Motorcycle Engine category,
    as well as to your builder page: tonyfoale's Homemade Tools. Your receipt:




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    Thanx for this tip, sure will help sort some of my problems.

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    Quote Originally Posted by Vinni View Post
    Thanx for this tip, sure will help sort some of my problems.
    What are your problems?

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    petertha's Tools
    I'm intrigued by your jig. In a former life I used to race RC models 'pylon racing' (200 mph, 0.40CI 2S methanol engines, 30K rpm). So shaft TIR is a similar big deal, especially after an unfortunate 'deep dirt injection' & you are now wondering if the shaft is still good. It is indeed a tricky object to measure accurately, worse on our engines because there is no stub shaft on the other end, just the counterweight/crankpin & annular gas passage hole. So even less to reference off of like end centers.

    But doesn't your entire principle rely on the main shaft being 100% true? For example if orange line is 100% concentric axis & red line is 0.001" (bent) deviation, isn't it just translating that deviation to your dial indicator as it rotates through the fixed bearings?

    MC crankshaft alignment and balance tool.-2018-04-03_12-41-53.jpg

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    Jon (04-03-2018)

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