Poorly lawnmower (Black & Decker GR280C rotary)

[Andy Mabbett]

I have a Black & Decker GR280C rotary lawn mower, which still works, but the blade keeps spinning loose once it's switched off - as it decelerates, the bolt which holds the blade in place unscrews.

I've put some pictures at:

Can anyone suggest how this can be repaired, or a part replaced, before I have to junk the whole mower?

Thank you.

[Tim S]

Andy Mabbett coughed up some electrons that declared:

If it's the metal bolt in a metal thread that's loosening, perhaps a drop of Loctite threadlock?

Tim

[Bob Minchin]

Make sure you use a grade of loctite that can be released otherwise you will never get the bolt out again. I'd suggest investigating the problem before resorting to this solution

It sounds like the bolt is not being tightened to really grip the blade. Maybe the bolt is bottoming in the shaft as a result of the plastic (looking) coating on the bolt becoming compressed or slipping in use. Maybe a washer under the head might get it tighter. My (very old - from the blue and white era) flymo had a bolt with a moulded plastic head that was hopeless. I now have an M10 socket head bolt and a big flat washer instead and it show no sign of slipping.

Bob

[Tim S]

Bob Minchin coughed up some electrons that declared:

Yes indeed.

I was thinking of bog standard Halfords stuff, which is Loctite 248, a medium grade thread locker allowing disassembly:

I had to, that's what I'd use. But as Bob has some excellent other suggestions, I'd try those first.

Cheers

Tim

[Dave Liquorice]

When my petrol mower started that trick it was because the diecast projections on the blade carrier had sheared off. Cured that by drilling holes and puting a couple of steel bolts in.

I can't see a hole in the blade to take such a projection or bolt head in your photos. Does the large disc contact the blade? Looking at the debris on the removed blade if it doesn't it's very close. How about bending the blade a little in the middle so the outer edges contact that disc and when you do up the bolt tightly the blade is forced straight and thus keeps the bolt in tension?

[R]

In 30 years of engineering I have yet to find *any* loctite that won't succumb to the heat from a gas axe or blowlamp.

[Bob Minchin]

Indeed most if not all anerobic adhesives give up at a 200 degrees C or so but I'd rather not use such methods near plastic components and bearings.

Bob