C.407 Engine Side Damper Stablizer

This C407 rubber damper for the left side of the engine on SS and Mark IV is also used on XK120 as a side damper, but not listed on the usual US vendors sites.
They have C4303 or C4794 as being front mounts for late 120.
Does anyone know if they are a good substitute?


they were also used as bumper bar mounts on MK IIs and MK Xs etc
Probably a UNF thread instead of BSF. But…

Ok I could believe that, a change in thread would mean a change in part number.
I tried to remove the bolt, but it turns without unscrewing. I suppose there is a threaded insert in the rubber that has come loose and turning.

So I removed the attaching bolts to the frame and those on the C483 torque arm bracket.
The torque arm seems to be welded to the C348 rear engine plate. Is that normal original?

Well mine is simply bolted to engine back plate.


Aaarrgh! That’s what I figured. DPO. :exploding_head:
Turning a 15 minute job into a 3 hour job.

Oh, jeez: where is that retroactive dope slap button???


Rob the hole in the bracket might be slotted, undo the bolts mount to chassis
then try to knock it out, if no luck a then a thin cutting disc to cut the head off the
setscrew, New mounts are most likely 1/2" UNF or 12 mm.
Peter B.

Brilliant, Peter, it was indeed a notch.
Not much swinging room in there as I had already put the coil back in thinking I’d come back to this another day.
Took about 100 taps with a ball pein even with a jack under the sump so it was clear of the chassis.

Yes later stabiliser brackets were welded on . A PO may have changed it over.
The weaker point is actually on the front engine plate at the 2fold where the rubber mounts are attached,
On the
Mk V this was changed to a separate bolt on piece.

It was both bolted and welded. I wonder, did they have a tendency to work loose; was that the reason for welding?
Mark V does not have this stabilizer at all.
It turned out to be 1/2-20 UNF thread. The part number of the bolt is given as C.390 or 38233 with no other remarks, so I don’t know if it was originally supposed to be BSF. It doesn’t seem to be mentioned in the '36-37 book. In the XK120 book it is NB.150/16D which is a 1/2-20 x 2" UNF bolt, used with a spacer.
Judging by the green paint on the rubber, this has been on this car a long time.

BTW the reason for this exercise was that I believe the exhaust downpipe is bumping on the steering box when I let out the clutch from rest. I will also be changing the front and rear mounts, which are the same as XK120 so readily available.

Hi Rob,

My stabiliser is just bolted and I’ve never been aware of it working loose. When I replaced my rubber chassis mount for the stabiliser I just bought an XK120 one so mine now has a UNF bolt in it.

I did buy an XK120 gearbox mount but the rubber was far too solid and transmitted vibration so I just went back to using my old soft one.

I’ve not had problems with the exhaust hitting the steering box. You might find that you can reposition the box on the chassis slightly if you don’t want to attempt bending the down pipe.


Changing the front mounts appears to have solved the bumping problem.
The old mounts were squished out to about 7/8" high and the new ones are 1-1/16" high.

There was also a 1/8" spacer plate under each old one, which I decided to also use with the new ones.
In order to do this job, I had to jack up the front of the engine about 2", which meant I had to remove the radiator and generator.

I found that there is a reason for the tapered shape of the base plate on these, for clearance past the wiring harness. The new ones didn’t have these tapers, it being not necessary on XK120 or Mark V. The notched bottom attachment turned out also to be necessary, the bolt hole spacing not quite matching, so I duplicated both features on the new ones with an air grinder.

The generator I had already restored, so now I’m stripping off the green paint on the radiator.
Both drain petcocks were stuck and the handle broke off one so I’m restoring those.

I’m waiting on USPS for a side damper stabilizer from Moss Motors, so if it is delayed and I get ambitious I may start on stripping the green paint on the front of the engine. I think they call it shipwright’s disease.

1 Like

The spacers on the front mounts were to be able to adjust the engine so that the crank nose and the crank handle hole in the chassis aligned

Ah, yes, the engine is now offset slightly higher than the hole in the chassis, perhaps 1/8", not enough to affect the crank handle, but something of which to be aware.
The new side damper mount from Moss had both the Moss 011-146 and XKs Unlimited C4794 part numbers on the bag; a sign I suppose that Moss is taking over XKs parts business, not a bad thing as I have always been happy with both sources.

Slightly different appearance but same bolt hole spacing and 1/2-20 UNF thread.
I noticed the screw I removed from the old mount is 1/2-20 UNF thread but the hex head size is for 1/2 BSF. Perhaps that is why it has part no. C.390 rather than an FS.108 number.