Allen Scythe – setting up the timing

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This topic contains 12 replies, has 4 voices, and was last updated by  andyfrost 4 months, 1 week ago.

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  • #31212

    irishallenscythe
    Participant

    After posing questions regarding wheels spacing in a separate post, I would now like help with the timing for my 1949 Model T Allen Scythe. The grass is growing longer by the day.
    As I understand it, the cut in the end of the shaft should align with the arrow on the brass flywheel, and both should align with the mark on the back plate at about 60 degrees before TDC, about ten o’clock.
    All three of these marks are there on my machine.
    But when these are aligned the points appear to open when they are behind one of the spokes of the flywheel, so it is difficult to see what is happening, and impossible to get the feeler gauge in between the points. Which suggests to me I am doing something wrong.
    But overall, if these three marks are aligned (if that is right…) then surely there is no other action required for the timing, just ensuring the points have the right gap.
    Can someone please confirm, or otherwise, that this is the right way to set the timing.
    I have googled the subject and got various suggestions off the internet, but nothing definitive.
    Many thanks in advance.
    Robin

    #31219

    andyfrost
    Participant

    5/32″ is the correct timing for a 25c, as the 25c has an over centre spark plug hole it makes life far easier , just set it so the points just begin to open at 5/32 BTDC , tighten flywheel , RE-CHECK that it hasn’t moved during the tightening process……….job done.

    Andy.

    #31221

    irishallenscythe
    Participant

    Thanks Andy – 5/32″ BTDC – I understand to be 5/32″ of the stroke in a vertical sense, so with spark plug out and a stick in, I have one line marked on the stick where the piston reaches the top of stroke TDC – and a line marked 5/32″ above that where the spark should happen.
    But what I am finding is that the points seem to be open for most of the flywheel revolution and only close briefly. I don’t understand how the flywheel shaft that moves the points can be circular, except for a small flattened area. The flattened area is where the points get a chance to close, but otherwise are held open. And if or when the governor kicks in, it completes the circular part where the flat part is, keeping the points open all the way round.
    And yet the spark is only formed when the points open briefly.
    Well, that’s how it works on the landrover. Is this system fundamentally different?
    In addition to which, when the points are just opening the points are behind one of the three ‘spokes’ of the flywheel and so I am unable to adjust the gap.
    I am mighty confused.
    Robin

    #31222

    andyfrost
    Participant

    Rather than confusing yourself further , try what I have said , and report back , as long as the points just start opening at 5/32 BTDC , it should be fine. You can set the correct point gap before doing the actual timing , it matters not whether anything is lined up or not , the gap will be the same any where on the stroke.

    Andy.

    #31224

    charlie
    Keymaster

    Gap should be set when points are fully open.

    #31227

    irishallenscythe
    Participant

    Well, all part of thinking too much, I was very dubious as to how to do what you said, but… you guys are amazing!!

    I did exactly what you said and I got a spark. I put the plug in and she fired up. Straight to it. No strangler open, no flooding of carb, but throttle wide. She turned over for maybe 4 or 5 seconds and then died. Subsequent tries she fired for less time each time and by the fourth or fifth try I just got one massive backfire with a foot long flame out the exhaust.
    So now I need to adjust something I guess…..Suggestions will now be treated with reverence!
    Thanks so much.

    #31230

    stuart
    Participant

    Think you need to check the ignition timing again as it sounds like the flywheel has moved on its taper / crankshaft.Be sure to tighten that captive flywheel nut otherwise it will loosen / slip (even more so if the main bearings are worn)!.

    #31233

    charlie
    Keymaster

    The way to get flywheel nut tight is to hit spanner hard with a hammer. Villiers did make a special spanner with a lump on the end for hitting with a hammer.

    #31234

    irishallenscythe
    Participant

    Thanks Charlie.

    What’s the best way to stop the crank from moving when you do this?

    #31239

    charlie
    Keymaster

    Whatever you do don’t use fins on flywheel to lock it. One method some suggest is turn engine until piston is about half way up cylinder, then push thin rope (starter cord) in through spark plug hole to fill space above piston. Then gently turn engine till it locks.
    I have used a Boa Constrictor tool to grip outside of flywheel.

    #31245

    irishallenscythe
    Participant

    Ok, I shall try stuffing cord in the cylinder.

    If the flywheel shifts slightly on the shaft unless fully tightened, how can I be sure that I have the timing right before I tighten the flywheel fully?

    If I try turning the engine over before I fully tighten, then the flywheel might shift, so I have to go through the procedure again.

    But if I fully tighten the flywheel and then turn it over, and then find the timing needs adjusting, I have to go through the whole procedure again, complete with fully tightening.

    Is there an easier way to determine that all is right before tightening?

    Or am I doing just too much thinking again?

    #31246

    charlie
    Keymaster

    Once timing is set it is a case of checking as you tighten. Once flywheel is a bit more than finger tight it should not move with further tightening.

    #31247

    andyfrost
    Participant

    One tip , make sure the crankshaft , and flywheel are THOROUGHLY de-greased beforehand , before de-greasing it does no harm to lightly rub the crankshaft with some fine abrasive paper.

    Andy.

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