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How to attach the blade to my Sun Joe electric wired lawn mower? I may be missing a bolt or screw.

The picture shows the mower, the blade and a cap which fits. But if I just put the cap, it will come off.

sun joe

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  • What is the purpose of that heavy washer with the hex inside? Looks like the hex fits onto the head of the bolt. Commented May 19, 2021 at 11:01
  • @dandavis, these are all the parts that I have :) I understand that I need to remove the bolt. But the hole on the blade is bigger than the bolt. Not sure how it will stay in. Also with the bolt in place , fact that blade came out means the blade hole was bigger. What do you think ?
    – John
    Commented May 19, 2021 at 20:32

4 Answers 4

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The central bolt and washers in the correct order are used to hold the blade to the mounting plate. The pins on the mounting plate, some of which may be broken in your case, fit into the off center holes on the blade so that the bolt need only keep the blade pinned to the plate and the pins support the torque. Inspect carefully. If you have missing or broken pins, your mounting plate or mower need to be repaired or replaced.

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I discovered that Sun Joe no longer sells the needed replacement parts for this model. This is the reason why I decided to fix it this way.

I used two stainless steel washers and a nut (from Home Depot) to replace the original plastic nut sitting behind the washers. I needed a pick to help me route the zip ties after I drilled two holes on the plastic back plate. The zip ties replace the function of the damaged pegs which use to hold the blade in place. The bolt should be tight enough to hold the blade in place so the zip ties should receive little stress during operation.

My Fix Using Home Depot Parts

Parts That I used

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    I don't see the ties lasting too long Commented May 10, 2023 at 1:15
  • You may be right, but the ties are cheap and easy to replace. The original broken pegs were made of plastic as well and lasted a long time. I was going to use rivets but the ones I had were not long enough. Also using rivets would have made the blade difficult to service or replace.
    – Gene
    Commented May 10, 2023 at 14:32
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    @RohitGupta If you're using a mower like this, chances are you don't have much to mow anyways. It's hack, but probably the best you can get, given the circumstances.
    – Machavity
    Commented May 11, 2023 at 13:01
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My first problem: My SunJoe MJ401E had a weird blade bolt that broke. The bolt had a plastic head - which holds the blade on - and a spacer that keeps the blade positioned. I assembled a replacement for the blade bolt which uses a normal bolt, with a fender washer - which keeps the blade on - and a nut in place of the spacer.

Parts list: -Bolt: M10-1.5-40mm fully threaded (so no shank/shoulder) -Washer: 1/2 in x 1-1/2 in. (or M10 x 40 mm) -Nut: M10-1.5

Assembly: Put the washer on the bolt, then tighten the nut all the way down.

My second problem: My mower blade has two small alignment holes slightly further out that's meant to accept an alignment stud to keep the blade in-place, but that stud is made of plastic and it SHEERS OFF?! To fix this issue. I just used a screw, which I tightened into what was left of the sheared plastic stud.

Parts list: -Screw: #14 x 1 inch

Assembly:

  1. Install the blade, aligning the pilot hole over the plastic bed of the sheered plastic stud before tightening the blade bolt
  2. Pre-drill a pilot hole for the screw in the plastic bed of the sheered plastic bolt, with a 1/8 drill bit
  3. tighten the #14 screw into the pilot hole.
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I've got same problem. I visualized same washer solution but instead of zip ties use small nut & bolt in a drilled hole (pair) on mount; keep bolt tight on washer.

Should work in light usage (thats all this mower for anyway!)

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