The C3447 anti-roll bar for early XK120 OTS & FHC is 0.591" diameter.
The C7220 anti-roll bar for late XK120 OTS & FHC and all DHC is 0.687"
diameter.
Going by chassis numbers in the parts catalogue, it would appear this change
occured across the board in August 1952 on all cars, not just SE’s.
The rubber bushings were C3056 early and C4349 late, the only difference
being inside diameter, so you could drill out your new bushings if you find
a later bar.
If your new bar fits, its probably not from a saloon, as they had wider
track.
Rob Reilly - 679187
The C3447 anti-roll bar for early XK120 OTS & FHC is 0.591" diameter.
The C7220 anti-roll bar for late XK120 OTS & FHC and all DHC is 0.687"
diameter.
Going by chassis numbers in the parts catalogue, it would appear this change
occured across the board in August 1952 on all cars, not just SE’s.
The rubber bushings were C3056 early and C4349 late, the only difference
being inside diameter, so you could drill out your new bushings if you find
a later bar.
If your new bar fits, its probably not from a saloon, as they had wider
track.
Rob Reilly - 679187
I forgot to mention the early bar I measured, originally removed from
679187, was also rather twisted and broken in the middle, a classic
torsional failure. I measured two bars from Mark V saloons and they vary
from .585 to .605 depending on where the measurement was taken, so it would
appear the early 120 bar was made from the same steel stock as Mark V and
the diameter varied a bit. These are the first two models with IFS, so
Heynes et al are still on the learning curve.
I also looked up the bar for XK140 and it is also the same C7220 as for late
120.
So we have a broken early bar and a broken late bar. This suggests two cars
that have seen a lot of extreme cornering in both directions.
Shearing stress is inversely proportional to the third power of the
diameter, and angle of twist goes inversely with the fourth power, so
coupled with the smaller diameter torsion bars of a non-SE car, and thus
more body roll, one would expect to see broken anti-roll bars more often on
early cars.
Has anybody else come across a broken anti-roll bar?
Rob Reilly - 679187>The anti-roll bar was broken in the middle when I got the car
Thanks for your note. The torsion bar on my 681431 is not a torsion
failure, but rather a straight break.
I picture some well meaning individual putting a towing hook on the torsion
bar to pull the car out of a snow bank in a blizzard at -35F and voila -
“SNAP”. Think 1966 or so.
I forgot to mention the early bar I measured, originally removed from
679187, was also rather twisted and broken in the middle, a classic
torsional failure. I measured two bars from Mark V saloons and they vary
from .585 to .605 depending on where the measurement was taken, so it would
appear the early 120 bar was made from the same steel stock as Mark V and
the diameter varied a bit. These are the first two models with IFS, so
Heynes et al are still on the learning curve.
I also looked up the bar for XK140 and it is also the same C7220 as for late
So we have a broken early bar and a broken late bar. This suggests two cars
that have seen a lot of extreme cornering in both directions.
Shearing stress is inversely proportional to the third power of the
diameter, and angle of twist goes inversely with the fourth power, so
coupled with the smaller diameter torsion bars of a non-SE car, and thus
more body roll, one would expect to see broken anti-roll bars more often on
early cars.
Has anybody else come across a broken anti-roll bar?
Rob Reilly - 679187