Johnson 5hp TD20 ignition timing facts & figures?

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This topic contains 20 replies, has 7 voices, and was last updated by Avatar larkbill 3 weeks, 3 days ago.

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    legendre

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    #14550

    Went all the way, and swapped the complete magneto plate from the good-runner to the problem motor. It’s too late to fire it up (neighbors..) so will report-back when I’ve had a chance.

    If this doesn’t do it, then I’m going to swap the carbs.. and if +that+ doesn’t do it, then I’m pretty well flummoxed.

    (I did try the carb swap earlier, but it was prior to diagnosing & correcting the air leaks in the intake. So that data is invalid.)

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    csw

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    #181801

    I’m sorry to have to crash this post, but I have a TD20 that I need to know how to set the points. It’s not like a newer motor, this the first one that I’ve worked on. Thanks Scott

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    lloyd
    US Member - 1 Year
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    #181803

    Compression on that motor should be at least 70psi cold and dry to idle down slow. 75 psi is ideal and about 77 psi is like new. Timing is fixed and not an issue, as noted above.

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    csw

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    #181809

    the compression is 70psi, what I’m trying to figure out, is does the crank need to be turned to set each set of points?

    frankr
    frankr
    US Member - 1 Year
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    #181811

    The crank is mostly round, except for the “flat” that causes the points to close when the push rod enters the flat. So, the points should be set to be open 0.020″ when the push rod is anywhere on the round portion of the shaft. If you have to rotate the shaft to get the push rod on the round portion, well sure.

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    larkbill
    US Member - 2 Years
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    #182097

    Frank keeps trying to lead you in the right direction, but you keep wandering off. It really sounds like you have a piston skirt issue. This motor has a pretty “roomy” crank case and thus a pretty low crank case compression ratio. It can’t afford to give away much and your low compression on the other side of the piston crowns is a warning sign. Piston skirts can be worn without being scored. It took a little digging to find the chart in my Johnson manual but the HD and TD have the tightest recommended clearances the JW being the only one fairly close. .0010-.0025 clearance on the skirts. Also crank mains are supposed to be .001-.002. It wouldn’t take much in both combined to cause a problem. Then add in TCW-3 oil with an effective weight of 20W. Could be your problem.

    Here’s something to try. An oldtimer (which I guess I now am) years ago told me he ran all his bushing motors on a 50/50 blend of 40 wt non-det and TCW-3 mixed with his fuel at the factory ratio. The 40 helped seal and cushion the bushings and TC kept fouling and deposits to a minimum. You might have to hit a farm supply to find the 40 wt. There is also a 50 wt aircraft oil that would work well too but the 40 wt is much easier to find and cheaper.

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