Jari Mower RIP

jari on fire

I am sad to report that the Jari mower bit the dust this weekend.  I purchased it about two years ago from a guy upcountry, and put several hours into getting it running well.  I sorted out most of the issues, including the frozen-up cutter bar and rotted gas tank, but the replacement tank never quite fit right – there was a slight intermittent gas leak between the top of the tank and the carb, and I never could figure out why.  However, on Saturday it finally caught up with me.  The mower ran out of gas so I shut it off, filled the tank, and as soon as I cranked it up a small flame started on the surface of the carburetor. I tried to bat it out with a mat of fresh-cut green grass, and it almost worked, but the flames persisted.  I ran over to the neighbor’s and grabbed two fire extinguishers, and exhausted them on it, but by that time the metal was hot enough that it re-ignited after the powder stopped flowing.

I didn’t think it would explode, since the gas seemed to be escaping from the tank – at first through the leak, and subsequently through the zinc carburetor, which melted into a puddle on the ground.  Still, I ran down the hill for some hoses, to tap the neighbor’s water.  At peak the flames reached 6-8 feet high, but by the time we had the hoses up there the gas had burned itself out, and the fire was reduced to burning the rubber tire, belts, and the thermoformed plastic fairing on the front.  Ben Wilkins tossed a couple of pails of water on the smoldering heap and the excitement was over.

Once it cooled off, Bodhi and Kieran rolled the machine down the hill and I took stock of the damage.  The engine was pretty well baked (as I mentioned the carb had completely melted), the left tire and shroud were shot, and the belts were burned down to the fiber cores.  But the frame was intact, and even most of the paint was still in good shape – I tipped the machine over on its side when it caught fire so the tank was up, and there wasn’t much to burn up forward.  One of the idler pulleys looks pretty baked, so it would probably need to be replaced.  Joshua and I toyed with the idea of doing an electric retrofit, since sickle mowers don’t use a lot of power compared to rotary machines, and using two separate motors would significantly simplify the mechanicals.  Unfortunately, I haven’t got time to do a major rebuild (or an electric conversion), so today I bought another used sickle mower (Troy-Bilt make) from a nice retired couple in Cornish – I’ll tune it up next weekend and see how I like it.

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4 Responses to “Jari Mower RIP”

  1. Ruben Says:

    I have been dreaming of a pedal-powered sickle bar…

    • fiveislandsorchard Says:

      Hah! That would be the thing to do. I should rig that up sans ground drive and hook it to the bucket of a tractor; have someone push me along and see if the amount of effort to cut thick grass is tractable. I’ve often thought about a multi-use pedal-powered cultivating tractor – my intuition says that ground drive and useful implement drive would be too much for a single pedaler, meaning it would probably be a light, spidery thing about 3 feet wide, carrying two pedalers fore and aft.

  2. Steve Says:

    Sorry to hear about your departed mower. Although, I used a Jari mower for a few years and many times wished it would self destruct in such a spectacular fashion. It was a newer one – single drive wheel, pathetic treads, unwieldy handles, break-y sickle sections.

    A self-propelled one would be a fun idea – electric assist would be needed though. There’s actually a fair bit of engineering involved in sickle bars, 90% of which I have forgot. As I recall the key is properly optimising the forward speed with the sickle bar design (both in terms of speed and orientation) because the force required to overcome the ultimate shear strength of the plant fibres increases noticeably when the plant is at any angle other than 90 deg from the horizontal plane formed by the shear/countershear surface of the cutterbar. There is probably a lot of efficiency to be found in this relationship.

    So, um, yeah, ground drive is the way to go!

  3. Ryan Grimm Says:

    First, glad to have found your blog through a ‘slow-bike’ FB page I’m on.
    Second, sorry to hear of the demise of your mower.
    The leak sure sounded like a float valve problem in the carb, either it’s getting stuck open, or the float itself was defective…a hole can wear in them, and they will sink, leaving the carb to run like a small faucet.
    If it had a diaphragm pump in the carb, that could have had a pinhole in it doing similar problems.
    A common problem, especially in single-cylinder machines that vibrate.
    If it used a common horizontal-shaft motor, it can be replaced. I did similar on a small Troy-bilt tiller, it just doesn’t have reverse any more. No big deal.

    The old horse-drawn sickle bar mowers I remember used one of the wheels to drive the sickle machinery, large teeth on the wheel digging into the turf gave it the traction needed to rotate the gearing. This incidentally aerated the soil a bit.
    If you can find one to look at, they were tough to kill. I’ve seen ones left as ‘yard ornaments’ for 50+ years and brought back from the dead as long as they left some grease in the gear box.

    The sickle teeth and bar needed yearly sharpening, and fairly frequent oiling IIRC. More frequent sharpening on tough grasses/large crops. Overloading and jamming the teeth kills their mechanical assemblies, and wears the teeth prematurely.

    The last time I worked on a powered walk-behind sickle mower was in maybe the late 1960′s, a self-powered behemoth that was old them, large and orange.

    Hope you get this figured out.

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