Modified Stag has Vibration Problems with Ford V6 Engine

[Mike Wattam <101714.1343@domain.elided>]

Hi Mike

Well, it's good news and bad I'm afraid.

The 3.1 litre engine was originally fitted in the Mk 1 Capri RS3100.  This
was basically a highly modified motor supplied to the UK police to make
their Granada's fairly rapid and able to catch a number of Cortina drivers
and nick them.

The Capri application was awful.  The ride was somewhat similar to falling
down the stairs riding a block of concrete.  The power-to-weight was
fabulous and acceleration could deposit surplus body weight in the boot. 
The back wheel adhesion was non-existent and any attempt at serious use of
the right foot had you disppearing over the horizon sideways or backwards. 
The other bad news was that it was all a bit of a blur because Ford in
their wisdom hadn't bothered with NVH and the vibration off the engine had
this habit of stirring your whole body into mud. 

Engine coarseness and vibration is always a problem with this engine
conversion, the engine anyway always was a 'nail' of an engine even when
new.  Ford when they got the chance of ditching this 'Essex' engine in
favour of the 'Cologne' 2.8V6 did pdq, as it was much quieter, smoother and
more powerful than the Essesx engine.  You can find out more about this
subject by reading the book of the Capri by Steve Saxty, he also mentions
as a throw-away line that the Essex V6 was originally designed to be a
diesel - that explains a few things..............

Now, I don't know what specification 'your' engine supplier has actually
used.  If he has either used a genuine RS3100 engine or gone for the
identical spec it will have a flywheel which was extensively lightened,
thus making the inherent vibration of this rather coarse engine much worse.
 I would suggest you try to find this out.  Therefore I agree with your
colleagues diagnosis, in that it probably needs a lot more flywheel, it may
be a good idea to go for a Granada/Capri 3.0 flywheel if not already
fitted, this will help.  The Ford V6 3.0 engine never was smooth, and even
in detuned form tends to vibrate in the Stag.  You can probably get a good
idea about flywheel weight by 'blipping' the throttle - an unusually fast
response both up and down is a characteristic of a severely lightened
flywheel.

It is not usual to balance engine-gearbox adaptor plates, so I would not
have thought these would be at fault.  However, it is possible that when
the convertor/box were mounted up to the engine, the afaptor palte was bent
if the gearbox was allowed to hang on it - I have also seen the centres
torn out of these adaptor plates, the first symptom of this is heavy
vibration.  Also, Ford at that time had a fiendish reputation for
inaccurately machined bellhousings so the engine ran out of line with the
gearbox - if more than about 0.020" this would cause a lot of vibration and
the drive plate would break around the centre within 1-5,000 miles

Another thing to check is the propshaft.  Any vibration problems inherent
in the engine will have a magnified effect if the wrong type of propshaft
is fitted.  The Ford application had a rubber sleeved propshaft which was
intended to even out torque vibrations, but the Stag auto propshaft is
solid.  Could also be your propshaft needs rebalancing.  Check this out by
fitting a couple of 'Jubilee' clips to the front end, does this make any
difference?

Look at the engine/gearbox insulation from the body.  The Capri mounts were
very soft, but these would have been scrapped in favour of the Stag mounts
and as the Ford engine is lighter, it will tend to 'wag' the car at
tickover.  If you can find some softer mounts, this should help.  Finally,
take a close look at the exhaust system particularly close to the cylinder
heads.  I can almost guarantee the manifolds will be in contact with the
chassis members and if so, you will need to do some cut-and-shut to sort
this out.  The Ford auto gearbox tends to drop onto the rear crossmember,
thus passing a lot of vibration back into the car.

Finally, the standard Stag exhausts run through the rear subframes both
sides and if this is still so, torque wind-up could be forcing
metal-to-metal at this point and the exhaust will have to be re-hung,
possibly using different insulators.

Hope this helps you.  Please let us know how you get on.

Mike Wattam
Triumph Stag Register