Hello Graeme
Lets see if can help you get to the bottom of your bottoming.
First and foremost, you can not use your "Eyechrometer" to measure
overcentre ---- period.
I will match my calibrated "Eyechrometer" with any Europa builder. I can
work to a few 1/10,000" on torque tube drive pin fit, and work with
1/100,000" fitting together a Cox .020 model aeroplane engine.
You need to take precise measurement, I initial tried to sight, no way can
you eyeball 1/16".
I fooled for some time with my gear on a solid fixture, with shock
absorber out and the tyre moved up and down precise with a hydraulic pump
jack. Very enlightening.
I suggest especial if you have your bungi out, take tyre off, and shock
absorber out but bolts in place and run swingarm up and down through its
travel, while you measure overcentre on the 3 points I initial described.
You need a thin straight edge, either thin high strength aluminium or
stainless. A thin ruler may work, but keep checking that straight remains
true.
You first need to get in your head the fact the further down the swingarm
goes the less overcenter things will be when LG08s are against stop, and
the further up the swingarm goes, the more overcentre things will become.
I have no doubt that pushing a pencil on paper, someone calculated loads
and birth of a undercarriage mounting frame was hatched. Remember that
this was unacceptable, as the overcentre load on the stops was failing the
frame. The reason for this failure you will see if you check as I
described, compress shock absorber and overcentre increases. OK then when
real world proved not strong enough, beef was added. Nothing wrong with
this.
On paper lets say 1/32" or 1/16" overcentre is called for, and on paper it
is proved that this is just fine. Is real world really the desired amount
of overcentre? Mine was not for sure. Was my LG08s really as per drawing
as far as placement of holes and position of stops? I have a fair share of
time welding 4130 tubing. Was proper fixtures used, correct length
components and order of tacking and welding proper, and calibrated sledge
hammer used to keep things on track really used to produce stops and pivot
points in the right place? Was my frame checked against a go no/go fixture
after it was completed? Also the top and bottom actuation plates, how
much bow are in these when you are trying to achieve 3.1", and then when
there is a bow, what point do you measure?
I needed to make a spacer or spacers (I forget exact but will check if you
need) to space 1 or both LG08s from UCMF. In addition I needed to releive
some of LG08 (perhaps both) to achieve acceptable clearance from UCMF. And
final I needed to grind the head down, quite substantial from one of the
bolts so it didn't hit the UCMF on the port side. Bottom line is all
components need to equate to overcentre. Any one of the mentioned can
skunk you into too little. My UCMF came in with a pretty poor excuse for
white powder coating on it, scratches and flaking abounded. Stripped,
sandblasted with Al/Ox, prmed and painted.
You will also notice that when you push the swingarm up, that clearance
between the downstop on tunnel and the lever develops. This is normal due
to increasing overcentre action. I anticipated that a bounce will grow
this clearance, and a relaunch as you describe will bang the lever hard
against this stop. I have my lever and stop angle tainted where the lever
will be forced inboard by a minor angle, and have lever bent so that there
is spring action pushing the lever inboard.
If you do not have access to obtain a proper measuring tool, E-mail me
with dimensions you need and I will make one for you, then you can give it
to the Europa Club for loan out to anyone who wants to measure theirs.
I could have welded a cap on my UCMF, but I already had it painted, so the
urethane inserts was a neat way to get precise length. I also did not like
the bang I was able to create when the LG08s hit the stops. The Urethane
helped out with bang. I first ground and filed stops till I had 1/8"
hitting LG08s precise, then made Urethane inserts to bring it to 1/16".
Worst case is it will be 1/8", probably OK, I would not want to try 1/4",
forces grow awful fast. I actual did calculation, and adding just an extra
1/16" increases stop loads on UCMF when shock absorber is compressed by a
lot.
I made a somewhat structural upstop for swingarm. It is a piece of 3/4"
marine plywood just ahead of the tyre and aft of the retracted shock
absorber. I have it glassed to the tunnel sides, and also screwed and
resting on a extruded aluminium channel that is drilled to look like swiss
cheese and glassed to the tunnel sides as well.
If your joint is with no movement between gear lever and LG08 because of
tight fitting bolts, Redux and Mod to stiffen this joint, and you truly
had some overcentre, then my dart throw would be your 3.1" grew to make it
undercentre.
That said I suspect you simply did not have enough overcentre, and
probably undercentre at least on 1 stop like mine, and you know the rest.
Please do a thorough inspect of your gear, make sure no broken or bent
components, please post exact over or under centre you find. Check to make
sure there is a secure mount to swingarm for the bottom of shock absorber
stuff.
I have my gear slot set so I need to pull pretty hard on lever without
bungee but with full undercarriage weight installed, this is the time I
set my 3.1" and also set my overcentre.
Good Luck.
Ron Parigoris
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