On Sat, 26 May 2007 20:00:39 +0100, "Davy"
wrote:



thanks for that Ian, I don't think many of us realised that the blade disc
has a built in facility for its removal.

It's very handy!

Regarding which is the correct bolt to draw the disc off the crank; garden
tools and mowers tended to have British Std Whitworth (BSW) threads. A 1/4"
BSW has 20 threads per inch and a obviously screw diameter of 1/4"; but you
say it has a diameter of 7/16ths - or maybe you meant across the flats? A
7/16th dia BSW is 14tpi so it can't be that. However a 7/16th dia BSF
thread is 18 tpi - maybe?
The outer diameter of the thread is, as near as I can measure it
7/16th. The AF is 5/8th. It could very well be 18 tpi so is probably
7/16th BSF
Not sure what you mean by it having three radii on it;
Looking end on at the head with a flat horizontal there are three
lines one pointing to the top flat (12 o'clock), and the other 2 at
120 degree intervals (i.e pointing to about 4 and 8 o'clock). Does
this help identify it
each but UNC/F bolts have
three circles in a row - I wonder if this is what you meant?.
No
A 1/4" UNC
bolts has is 20tpi and 7/16ths across the flats - if you did mean 'across
flats' then this is a good match to what you have. But a UNC thread is
wrong for a British lawnmower. So my guess is that the Hayter Hayterette
requires a 1/4" BSW bolt; but that someone gave you
I actually got it at a local garden machinery place who knew about the
technique when asked and also knew the correct (allegedly) bolt to use
as the withdrawal tool. But he didn't give me it!
a 1/4" UNC bolt which
will screw in to a 1/4" BSW thread; but a UNC thread is cut at 60 deg whilst
BSW is cut at 55 deg; so the mismatch will give a weak interaction because
the stresses are not transmitted through the flanks of the thread.
My knickers also twisted at this point!
But none of this is making sense to me because I think I understand you to
be saying that your withdrawal bolt screws into a thread in the centre hole
of the disc? - and that "When the retaining bolt is out, the thread in the
crank is actually smaller than the hole in the disc through which the
retaining bolt passes" The retaining bolt which goes into the crank has a
diameter of about 5/16ths - larger not smaller than 1/4".
All my 'measurements' relate to the bolt to draw off the disc. This
bolt _is_ of a larger diameter than the retaining bolt
I think my knickers are now sufficiently twisted to hand the subject back to
you!

cheers

Davy

In reply to the other issue in the thread (no pun intended) concerning
age of the equipment and the possibility of metric.......my 'new'
machine which definitely has this arrangement was bought 'just'
secondhand in about 1989/1990 . I think it was made in 1988/9. Other
bolts for handles cowlings etc are, I'm pretty sure, metric.
My 'old' machine is significantly older - given to me to tame the
jungle when we moved in here in 1987. The FIL was not known for his
generosity so I guess it was totally depreciated by then! I guess
manufactured at the latest 1975. Now, it doesn't have any metric bolts
on it to my knowledge and I don't think I have ever had the disc off
but I _THINK_ it was the donor who told me how to get the disc off
using the integral hub puller.
If it wasn't peeing down I could go and try and get the retaining bolt
out I suppose but having been stood outside for the last 2 years and
not been used other than for pinching spares for the last decade that
could take a while!!

Please reply to group - email address is not monitored
Ian