68 Bentley T engine rattle under load.

Interesting thought re starter motor. Doesn’t feel like that but there is definitely something catching, metal to metal, gets worse when the engine load is increased. I have also changed the starter motor to a high torque one and the problem is still there.

re brakes. I used a Wilwood tandem brake master cylinder fitted where the original master cylinder was located. Think it was 1.75“ bore but would need to check. (Checked - twin 1 1/8” bore) This then goes off to two remote vacuum servo in the boot/trunk. Vacuum comes off a tapping on the inlet manifold. The servos are hidden behind a carpet covered panel, I lose some space but theres still loads of room. The brake lines then return to the rat trap and feed into the two circuits, one for one of the front brake callipers and the second for the other front brake callipers and rear callipers. The tandem master cylinder is fed from two separate reservoirs which in turn are fed from the existing brake reservoir. It all comes together and works fine with progressive braking and if I need to stomp on them they stop the car very well indeed. My choice to go down this route of course. Just couldn’t hack the malarkey of the original set up and it’s diabolical maintenance requirements.

I also installed 2psi residual pressure valves into both circuits to ensure brake effect is pretty much immediate when the pedal is depressed.

In post 23 I asked you to disconnect the drive belts to eliminate the fan clutch as the problem, just spinning it by hand doesn't tell you much unless the bearing in it is totally shot.

In this case the bearing is a little dry, but not binding.
The car drives well until you put a load on the bearing and gives you the noise you hear.
Stepping on the gas forces the bearing to move causing the problem.
When spinning as a mass, it's quiet until the bearing in the fan clutch starts to move.
The metallic sound is coming from the "chattering" of the bearing underload, and it's being transferred into the metal blades of the fan.
That metallic vibration sound is coming from the fan.
All this changes when the engine is cold and the viscus fluid is thick putting a load on the bearing _ at idle.

It's such a simple thing to remove the fan clutch drive belt(s), when compared to removing the trans; and all the other things you've done.

I would be surprised if it wasn't the fan clutch.

Ok thanks will check when I fit the new one.

Revving in park does not creat the rattle. Only in drive on the road, or loading in the engine in drive with the brake depressed. It will be quiet for the first few minutes as the car warms a little, and then starts to rattle under load. It never rattles whilst decelerating or coasting or lightly loaded.

My head is telling me it’s a tappet failing, maybe my phone exaggerates the noise to be more tinny than it is. It’s a hammering noise relative to engine speed (it could be double engine speed but hard to tell). It is not a main bearing rumble, I have had that before on a different car and it’s not that. When the rattle starts, putting more load on the engine makes the rattle louder and at its worst it becomes a continuous graunching noise. Getting off the gas eradicates the rattle/noise.

Whilst my head says tappet I am struggling to see how that would be engine load related. There should be no extra load on the tappet when engine is loaded compared to when engine is free revved. Only other thought is it’s relative to air/gas flow through the engine. I Borescoped the engine cylinders and didn’t find anything alarming. Maybe some minor foreign object damage on one piston. It’s not coming from the exhaust manifold or system. Given I haven’t found it yet from various inspections/tests it feels like it is going to be something odd. Thanks.