Hi, solved, but wanted to share this with you in case you encounter the same problem.
I noticed a clunking noise at the front end when a torsion was applied to the bodyframe (e.g., when driving up a curb with the left or right wheel) or due to a pothole. I suspected the suspension but everything okay there. I spent some further 20 hrs to investigate where the noise came from.
The rods on top of the engine that increase the rigidity of the body are fixed at the bulkhead and at both wings. The bolt that fixes the rods to the bulkhead had some play. Covered the bolt thread with some heat shrink tubing around it, tightened the bolt and no more clunking.

 

thanks for taking the time to describe your problem and explain the solution. now it's a searchable problem/solution resource. too often members list their problem but don't explain if the issue was resolved and how.

 

yes the torsion bars must be really tight to prevent flexing when the engine torques. E types have them too.

 

Jose, I believe the torsion bars on E-types refer to the twisting bars that replace a front suspension spring (like those fitted to our XJ6/12's). I think Willem is talking about the V-shaped bars (tubes really) that prevent the XJ front end from twisting under stress. I would prefer to re-bush that bulkhead fitting instead of taking up any wear with a plastic insert.

 

Hi Jose, yes that's the V-shaped bars on top of the engine and which are so awkward when working on the engine.
I agree that re-bushing would be the best way to go.
I must say that two garagists had already failed to find the cause of the clunking, it was driving me nuts.

 

hi: assuming "garagists" = mechanics, failed to find the cause. that doesn't surprise me. they are not vested in your car as you are. how much time did they really spend on the road trying to duplicate and locate the noise? not much would be my guess. i'm not against hired help but these cars require a special someone that is patient and methodical. it's great that you determined and corrected the problem (well maybe not in the best long term fashion). and again, thanks for letting us all know.

 

yes Iramphal, those are the torque bars, but I see E types with the same over-the-engine torque bars. i have also seen them in Maserati Quatroporte, same thing.

 

yes I have removed those from my car to repaint them glossy black. They are quite heavy steel. The bolts are 9/16" if I remember correctly. One bolt at the cowl where the two bars meet and one bolt at each wing. I have the bolts and nuts torqued at 50 lbs. more or less and I added a locking washer.

 

Yeah, those braces need to be really tight or they'll make noise.

While we're on the subject of clunks, the front shocks often clunk from worn upper bushings and/or not-tight-enough lower mounting bolts. I've found that those lower bolts have to be really, really tight to prevent noise. Tighter than you'd typically think. Those noise is identical, IME, to the noise from the engine bay braces.

Cheers
DD