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Thread: Slick 4201 and 4301, educate me

  1. #1
    zenairdave's Avatar
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    Feb 2015
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    Slick 4201 and 4301, educate me

    I am getting around to learning about the 100/500 hr services on my O200 mags, 4201 and 4301.
    For two years of ownership, I have assumed the different numbers were similar versions of the same mag, one with and one without the impulse coupling 25 degree delay.

    Based on that, I thought I had two properly working mags, one with an impulse.
    After some research, I now believe they are just old and new versions of the same thing, both marked with the 25 degree lag angle but, I only hear one click. It could be they are impeccably timed and click together but I don't think so. Here is the question.
    Is it possible for something to break in the impulse coupling that lets the mag operate as a normal non lag mag? Running checks on L, R and both seem to have normal drops.
    Can an impulse coupling lock and work as a non lag?
    I am trying to understand this before hooking up the timing box this weekend.

  2. #2
    hotrod180's Avatar
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    May 2008
    Port Townsend, WA
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    Generally, Continentals have an impulse on each mag, and Lycomings only on the LH mag.
    I have Bendix mags on my O-470 and they are both the same model.
    Had Slicks on my olld C170 but I don't recall whether they both the same model or different models.
    Cessna Skywagon-- accept no substitute!

  3. #3
    Cub Builder's Avatar
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    Mar 2011
    Northern NM
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    The 4201 model is the obsolete version which was replaced by the 4301. Both should have impulse couplers. If there is any question about the impulse couplers, the mags should be removed so the impulse couplers can be inspected. I suspect you will find they do indeed click together. I have seen an impulse coupler stick so it would not function when the plane had sat for an extended period, but once the engine had been started, the counterweight on the impulse pulled it loose so it was functional. The more typical failure mode for an impulse is if the rivet the counterweight pivots on is worn through, or the pawl that the impulse catches is worn through. If either case is true, the mag should be removed for evaluation before any further flight. There was a problem with the rivets years ago, which had an applicable A.D. and should have been corrected. The rivets wearing lead to damage of the pawls, and caused some magnetos to have the counterweights come off, usually destroying the magneto. However, dire warnings aside, if you have been flying it like this for a couple of years, I'd bet that your mags are set to where both impulses are firing at exactly the same time.

    -Cub Builder

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