Mower blade attachment keeps failing

[Paul in the woods]

A friend has a McCulloch mower where the blade is attached to an adaptor that then drives a belt for the front wheels. This attachment has a star shaped fitting that grips the blade. This star shaped fitting has failed a couple of times now causing the blade to come off. The first time may have been caused by a stone but this time it seems to just be long grass.

 

Does anyone have any idea why this is happening? Could it be the bolt needs tightening up to a specific torque (if so anyone know roughly what?).

 

This is the part: https://www.ransomspares.co.uk/parts/brands/mcculloch/lawnmowers/m56-190awfpx (96141026202)/blade-adapter/420223.htm

 

Seems to be a Husqy part so I would expect it to be well made. Having said that there's plenty of reviews over the pond saying the part often fails. https://www.amazon.com/product-reviews/B013TDMEU8/ref=acr_dp_hist_1?ie=UTF8&filterByStar=one_star&reviewerType=all_reviews#reviews-filter-bar

Edited July 7, 2020 by Paul in the woods

[adw]

Slightly worrying that a blade comes off, so insuffiently tightened, blade bent or unbalance, bent crank causing in balance. Blade bolt in the book says 70nm.

[Khriss]

Hmmm. Shot in the dark -  would be the washer on yr blade to press it against the star.  Bigger washer or bigger bolt head. K

[Paul in the woods]

Thanks both. I think the first time it broke at the pulley end. I will ensure the new one is tightened fully and enquire if both of the washers were on the bolt when it was replaced. (Both times the bolt also broke).

[Paul in the woods]

Does anyone know of anywhere else in the UK I can source parts? The attachment is £27 which I can understand but the bolt and two washers are over £5 each.

 

And does anyone know if there is anything special about the lock washer or can a normal split washer be used? (Obv £7 is cheaper than a new mower but £7 for a split washer, does it need to be gold plated?)

[adw]

Mucculloch consumer brand is handled by Husqvarna, in Newton Aycliffe, bolts breaking and blades coming off are the things of horror films, I would contact them and relay what is going on here before somebody gets hurt, don't go fitting non genuine parts as this will muddy the waters.

[mikerecike]

Often you need a Belleville washer, not a normal washer. A Belleville washer looks like a washer but is more of a coned spring - they're used for a reason.

Edited July 25, 2020 by mikerecike

[spudulike]

1 hour ago, mikerecike said:

Often you need a Belleville washer, not a normal washer. A Belleville washer looks like a washer but is more of a coned spring - they're used for a reason.

Yup, as fitted on MS200T exhausts or not on the ones that fall off or come loose!!!

Also used on the many press tools I used to set and run in a previous life!