I now know how to do this.

Cutter disk is held by a 3/8 UNF bolt (9/16AF or 14mm socket - either fit
just as well) and a woodruff key to prevent rotation. Bolt can be very rusty
and tends to be worn smooth by contact with hard objects; would be better to
replace but is unusual so would need to order.
Recommended to jam cutter disc with a mole grip which will jam against a
piece of wood against the mower skirt. Retaining bolts needs a lot of torque
to get off; is said to be high tensile so head will not shear off. Recommend
a six-sided (not usual 12) socket. If this fails then weld a long bar to the
nut.

The centre of disc is threaded so a 7/16 UNF bolt can be screwed in against
the crankshaft end and will force disc off. Need to put a spacer in to
prevent threads in crankshaft being damaged. If disk has not been off for a
long time then woodruff key is likely to be rusted into the keyway and disk
will be difficult to remove. Disk is thin so has only a few threads and
these are likely to strip. Some resort to WD40, blow gun and big mallets.
Some cut the disk off. If done by a dealer then expect an hour at £30.

Examine disk for cracks - if it disintegrated at speed then not funny. If
blade bolt holes are elongated then needs a new disk.

Whilst disc is off, allows access to oil drain plug so oil can be changed.

hope this helps,

Davy

"Davy" wrote in message
om...
I am servicing a Hayter Hayterette mower and need to remove the large
metal
disc that the bladelets are attached to so that I can replace them. I
assume I undo the nut in the centre. But how to stop the disc/shaft
turning?
And does anyone know which way the disc rotates in use - I suspect that
the
bladelets are on the wrong way round!

cheers

Davy