[xk] Alloy Flywheels

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From: “JAGPRO” jagpro.geo@yahoo.com
To: xk@jag-lovers.org
Subject: Alloy Flywheels
Date: Wed, 7 Mar 2001 13:25:04 +1100

Hi! Listers,

In respect of the many Alloy Flywheels made for XK engined Jags, I have
fitted various makes often the same flywheel with various brand names.

The best fitting Alloy Flywheel and the one with the best longevity in my
experience is the GTJ.

The all important Section through the bolt up area of the GTJ is correct &
the strongest in that area of the as used and or inspected by me , US made
Flywheels , the GTJ Flywheel fits nicely onto the Crankshaft Flange some
others then GTJ have the bolt holes symmetrical and people file the holes
out, bang it on with a mallet to fit it. A Jaguar Flywheel only fits on
way the holes are not symmetrical one vendor had their flywheels made with
symmetrical holes then filed the holes out before despatching and or

The filed out thinner mounting sectioned flywheels are known to be
and also the ring gears are moving, this I predicted after perusing a
particular line of Alloy Flywheels & advised that Vendor of the Problems I
realised and of expected problems in service.

Some Vendors have parts made and do not test properly before marketing
find out the shortfalls in their products by testing on their clients.

I try and use well known long-time brand names sometimes we have to use
unknown because there is no alternative,with alloy flywheels the one that
has been around the longest is a more comfortable decision for me.

All Alloy Flywheels do not last as long as a Steel Flywheels because of
Inserts used, however they generally last as long as the driven plate does
then a new insert can be fitted easily at clutch O/haul time.

I personally don’t see the need for an Alloy Flywheel the Jaguar Steel
Flywheel can be lightened sufficiently with the use of the 9.5" Diaphragm
Clutch assembly and even further for a Triple Plate Clutch Assembly, the
latter is not suitable for road use.

The little less weight of an alloy flywheel out from the centreline gives
me no measurable performance gain on the track or on the road.

The overall weight saving of an alloy flywheel does not count to me, its
weight on the extremity of any Flywheel that matters to me.

If one machines the steel flywheel down to the thickness of the ring gear
right up to the diameter of the Clutch Cover assembly and removes metal
the back of the Steel Flywheel as on the early E Types that works fine for
Road Cars & Club Racers,when one goes real fast and needs to change at
racing speeds the 9.5" Clutch will not do the job & a triple plate clutch
needed, then the steel Flywheel can be made very light and still be very

When one takes weight from the flywheel end after a point it needs to be
into the Harmonic Balancer otherwise Harmonics encountered at high &
necessary Race Revs can & will break a Crankshaft.

I use the GTJ Harmonic Balancer as first choice, the OZ made XK engine B&M
Balancer developed by Norm Lutz & Professor ? at Melbourne University is a
push on interference fit and does not become part of the crank as the
Tapered Cone set-up of the standard Jag Balancer or as the GTJ Balancer

The old Style 3.4 & 3.8 Balancer really is a dubious design and the re
bonded units leave to me some shortfalls to consider for use on a high
performance engine,the later 4.2 XJ6 Balancer is if in good order a much
better choice.

I have been using the same lightened Steel Flywheel and Triple Plate
since the 1970’s, another Sydney Racer Lionel walker has been using the
Steel Flywheel Clutch set-up since the early 1980’s, save that we both
have----- Original Message -----
replaced the friction plates.


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