|
Flywheel
- Pre-Verto types. |
21 November 2000 |
The early
spring-type clutch flywheels are of no use except where total originality is required
on a concourse car. The taper is too small and diaphragm pressure ring
non-existent. No use to man nor beast.
With the
exception of the fact the two-piece flywheel is two pieces bolted together -
this and the later one-piece cast item can be treated as the same thing. They
will universally fit all transverse engine cranks from 1964 onwards, so that
should be easy enough. If all you can get is the hulking great 1300 type, then
this too is as universal to fit, but I highly recommend you get that extra cast
lump machined off of the outer edge as a bare minimum.
Further
lightening of these cast flywheels is possible by having metal machined off of
the diaphragm side, from the outer edge of the diaphragm pressure ring
outwards. A safe amount is 0.200". I have taken considerably more off, but
wouldn't generally recommend it - the 0.200" is enough to make a big
difference. Keep a note of what thickness of material is removed, as you will
need to fit spacers under the clutch straps to maintain the correct fitted
height. I generally use 3/8" flat washers.
It is
IMPERATIVE the clutch drive straps are set at the correct height. Many get this
wrong and end up with a slipping clutch for some seemingly unfathomable reason.
The following should be carried out if the flywheel or pressure plate has been
machined, or you are using parts you have no history on:
·
Place
the pressure plate 'horns' upper-most on something to hold it off of the work
surface
·
Place
the clutch plate in position, with the protruding primary gear spline boss on
the underside facing the work surface.
·
Place
the flywheel in position.
·
If
the drive straps are holding the flywheel up, or are under tension pressing on
the pressure plate 'horns', more spacer-washers/shims are needed between the
drive straps and flywheel.
·
If
there's a gap between the drive straps and pressure plate horns, the spacing
between the straps and flywheel needs reducing.
·
If
no drive straps are fitted, using a straight edge or drive strap fitted to one
of the horns, measure the existing gap between flywheel surface and underside
of straight edge/strap, and make suitable spacers to this measurement.
The idea is
set the straps so that when in 'as assembled' position, they are not under
tension, nor are well clear of the pressure plate horns. They should be JUST
touching. Under tension the clutch will slip due to decreased clamping
pressure. Too far clear may cause disengagement problems.
 |
Click to Enlarge the image |
Marking the
timing marks on the outer edge of the flywheel adjacent to the original marks
prior to machining will allow them to be re-marked afterwards. And if you are
very friendly with the engineering company, material is removable from the
clutch plate side too. Check out the diagram for details. BUT, and a big BUT,
these are only suitable up to fast road use. High rpm use, even if only
occasional, can see them shatter. Believe me, you do not want lumps of cast
iron visiting you in the cockpit having just left the crank at 8,000rpm! Even
more weight-saving can be achieved by the fitment of the automatic Mini ring
gear (part no 22G2613) as this is much thinner than the standard manual one -
0.343” thick instead of 0.500” - therefore lighter; most importantly where it
counts - on the outside diameter. This will also allow the ring gear register
to be machined down to the thickness of the thin ring gear.
From here
we go to the specially produced flywheels turned from billets of good quality
steel. Until recently there was only an ultra-light version available (well,
two actually - more of this later) until Mini Spares fulfilled the desire of
many by producing a street version of the ultra-light item. Essentially an
ultra-light steel flywheel without the outer lightening slots machined in. Both
types are fitted with the lighter ring gears as standard. This neatly filled
the gap between serious road use and occasional sprints and hill climbing and
full race use without the alarming possibility of mid-race appendage removal by
flying iron debris. For direct weight comparisons of the aforementioned,
consider the table below.
FLYWHEEL
WEIGHT COMPARISON
|
|
LB |
KG |
|
Standard iron flywheel - unmodified |
16.71 |
7.58 |
|
Standard Iron flywheel - modified |
13.36 |
6.06* |
|
Steel light-weight flywheel |
11.02 |
5.00 |
|
Steel ultra-light flywheel |
8.38 |
3.80 |
*Note -
this is the safest recommended weight with above machining details.
See
'Flywheel & Pressure Plates - Effects of lightening' for benefits of
lightening.
For years there
was more or less only one ultra-light version available. During development of
harmonic dampers, Mini Spares came across some odd harmonics on the engine they
were using as a test bed. It was causing inconsistent harmonics up and down the
rev-range that were potentially failure-inducing of the whole crank assembly.
And something that a harmonic damper would not necessarily totally arrest.
Investigation with a strobe highlighted the outer section of the flywheel
flexing, caused by the extended thin section of the outer edge/ring gear. So
they made their own, splitting the original three long slots and three round
holes into six even slots. Problem solved!! This also allowed them to address
consistency problems experienced by the then lone supplier such as incorrect
crank taper and clutch face angles.
A couple of
modifications worthy of note are thus -
- For all race applications, and
big output road units, use THREE clutch straps for each location on the
pre Verto set-ups. This eliminates strap stretch and horrid vibrations.
- If you have the friction face
of the pressure plate re-machined to make it flat, make sure the exact
same amount is machined off of the three ‘horns’. Failure to do this will
mean severe clutch slip and ineffective disengagement.
- On performance road cars to
help prevent fretting/fusion-welding of the flywheel to the crank, torque
the flywheel bolt up to 125lb
- On race engines the above
procedure should be observed, except I always do this three times, rapping
the flywheel with a dead-blow or copper mallet against the clutch spring
ridge between each re-torque. May not be the ultimate, but I have NEVER
had a problem doing it like this - and I've seen all kinds of rituals
observed for this one!
Useful
part numbers:
|
C-AEG421 |
Light steel fast road flywheel, inertia ring gear |
|
C-AEG420 |
Light steel fast road flywheel, pre-engaged (Verto/Valeo) ring gear |
|
C-AEG619 |
Ultra-light steel flywheel, inertia ring gear |
|
C-AEG620 |
Ultra-light steel flywheel, pre-engaged (Verto/Valeo) ring gear |
|
2A3657 |
Diaphragm to pressure plate bolt, 3 needed |
|
2A3658 |
Clutch drive straps, 6 standard, 9 for up-rated/race |
|
2A3659 |
Clutch drive straps to flywheel bolts. |
|
2A3512 |
Lock tab, clutch drive strap to flywheel bolt - 3 needed. May be no longer available (NLA) & only available in clutch lock tab kit 18G8086 |