Lawnmower blade retaining nut - clockwise or anti?

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geekIT

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#2185983 23-Feb-2019 17:55

The blade tips must be able to extend straight out as the blade rotates. If one is stuck folded that would easily explain the vibration.

9/16" is 14.3mm so a 14mm socket will be a snug fit. The bolt is 3/8 UNF not metric.

I usually jam the blade with a piece of wood.

I finally managed to remove the blade. The bolt was a left hand thread.

No, just kidding :-). Conventional RH thread.

The tips don't rotate very freely. I guess they rely on centrifugal force to keep them in line with the blade-holder, but they still seem pretty rigid to me.

Anyway, I CRC'd them and then added ordinary oil. They're held on by locknuts so they can't be over-lubed.

I didn't run the mower without the blade in case, as you pointed out, the weight is needed as a flywheel.

But I will return it to M10, I still think the vibration is excessive.

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tdgeek

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#2186000 23-Feb-2019 18:31

geekIT:

Bung: So we all have all the details.

What is the model of mower and what type of blade is it?

If it is a blade holder with swinging blade tips it is possible that one tip is stuck not fully extended, that will unbalance the mower. A fixed blade would need obvious damage to unbalance it after just 10 mins running.

The mower probably wouldn't run well without a blade as it could act as part of the flywheel.

If it is a Briggs & Stratton engine the bolt will be a normal 3/8 x 11/4" UNF not lh thread.

Okay, the machine is branded on the (red) shroud 'Vinaro 350ST'. There's a plastic plaque on the front labeled 'MORRISON'

The engine is a B&S 500E, 140 CC OHV. Made in USA.

I took a look at the blade, and yes, it has add-on tips.

You say 'swinging' blade tips - does that mean these bits should be rotating freely? Because they don't. One is pretty much locked in place, the other moves if I twist it.

Incidentally, the bolt head exactly fits a 14mm socket. I tried again to undo it as I would a conventional rh thread , but it wouldn't move.

Shame these things don't have a locking button like most skilsaws.

I'll find a way tomorrow :-)

The tips move. Being tight is normal. if you had a fixed blade and you hot a solid object, bye bye crankshaft. The tips will fold back, centrifugal force will put that back into place. If you don't regularly mow bricks :-) they will get tight

tripper1000

1617 posts

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#2186262 24-Feb-2019 12:37

Are the tips in good condition? If they are a dis-similar weight due to wear and/or damage that will cause vibration (that is one reason they need to be periodically replaced). Also, if someone has fitted the tips with different length bolts, numbers of washers or otherwise messed up the left to right weight balance, that will cause vibration. You can test-run the mower without the tips fitted to narrow the cause of the vibration down.

If one tip gets stuck folded in, the imbalance shakes the mower quite violently - "excessive" would be a conservative description.

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