Before I can get on with some serious testing, I needed to connect the throttle linkage - from the pedal to the carburettor. It's one of those jobs I was looking forward to as it's another 'thing' that physically joins the engine to the car and so makes it 'whole' again.
It's useful to understand the mechanics and parts of the linkage and the parts books are a good reference here.
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| Throttle linkage parts |
There are some scant instructions for setting up the throttle mechanism at Operation D.142-0 in volume 1 of Manual 814.
Though they are pretty brief and don't go into a lot of detail - particularly in terms of rod alignment. Elsewhere in the manual the instruction is simply to 'align if necessary'. Here is how to go about it.
The Relay Arm - the Horizontal Control Rod
The relay arm transmits (relays) pedal movements and position to the carburettor. It's the horizontal rod at the back of the engine (part 9 in the diagram above). You haven't really got many choices when it comes to fitting the arm to the carburettor. At the carburettor end, the arm connects to the butterfly shaft.
The relay arm itself has a star-shaped end which provides some flexibility against engine movement and mis-alignment. The flexible joint also takes up engine movements during acceleration and deceleration.
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| Relay arm fixing at the carburettor end |
That's key because you want the rotation of that control rod to be as 'knot-free' as possible. The relay arm needs to be as in-line with that carburettor shaft as possible - both in the horizontal and vertical plane. Think of it as needing to be an extension of that shaft. Adjustment is done from the back, bulkhead end, not the carburettor end.
The relay arm end passes into a brass bearing suspended in rubber, on a flat metal counter plate.
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| The relay arm end is suspended in a brass bearing |
The counter plate has vertical slots and you can use these to set the horizontal orientation of the relay arm.
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| Vertical slots in the counter plate |
Check the condition of the rubber membrane in that counter plate. As the rubber perishes, the operation of the pedal on the relay arm pulls the bearing down and out of any previous alignment made. Tin fact the bearing - and so the relay arm - can fall out of the rubber completely. Replacement plates are widely available but be aware that there are two diameters of relay arm rods and so there are plates with different sized bearings.
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| New and worn counter plates |
If you are buying a replacement plate, measure the diameter of the control rod that needs to fit through it. You could use a drill bit to work out the hole size.
In trying to make the relay arm inline with the carburettor shaft, if you find that the bolts through your counter plate are at the very tops of the slot (i.e. the plate is as low as it will go) - but that the relay arm is still not in line with the carburettor shaft - this may indicate that your engine is sloping down towards the back. This could be because the rear engine mounts are set too low or - more likely - have worn and have sunk..... Time for new engine mounts.
Similarly, when viewed from the top, the relay arm needs to be attached to the carburettor shaft as square-on as possible.
The bracket on the bulkhead lip that the plate fixes to, has a horizontal slot, so the plate can be moved across it to align the rod as necessary.
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| Horizontal slot in the black bracket |
If you find you have used all the slot width and still find that the relay arm still isn't perpendicular to the mount on the carburettor, this may be because the engine is sitting at an angle across the engine bay. Ideally, the back end of the engine should be aligned so that number 4 spark plug is as directly below the hole in the scuttle as is possible.
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| Ideally the spark plug should line hole in the scuttle |
If it's not, it's not too problematic. By loosening the rear engine mounts from their plates on the chassis, the engine can be carefully 'nudged' across a little. Or you may just choose to live with it....
As an aside, I've see the bracket fixed upside down - on the underside of the bulkhead lip. The counter plate is then also fitted upside down to try to compensate....
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| Bracket and counter plate fitted upside down? |
Unfortunately in this wrong configuration, the highest setting you can achieve for the plate, is only about equivalent to the lowest position you can get if assembled correctly.
With the horizontal relay arm position set, you can move on to the vertical lever and rod at the back of the engine
Spring Adjustment
The shaft of the throttle pedal.......
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| Throttle pedal assembly |
......passes through the bulkhead and it's end protrudes at the rear side of the engine - near where the timing chain cover is.
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| Throttle pedal shaft in the engine bay |
The tip of the shaft has a flatted section. The lever of the the vertical control rod is fitted to this and secured with a pinch bolt.
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| Lever fixed to the pedal shaft |
Operating the pedal twists the pedal shaft, which cranks the lever, which pulls the vertical rod down. The relay arm at the top is then operated indirectly through the action of a pair of springs. The springs are slung between the nylon bushes on the horizontal relay arm.....
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| Springs on nylon bushes |
........and a small triangular hooking plate (part 8 in the diagram above) on the vertical control rod.......
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| Hooking plate on the control rod |
With your foot on the pedal, the springs act to pull on the relay arm and so operate the carburettor. When you lift your foot from the pedal, the springs also pull the control rod and pedal back up. Spring tension needs to be such that, the springs can fully lift the pedal and fully close the butterfly of the carburettor. If the spring tension is insufficient, the throttle will feel 'sloppy' and will affect engine responsiveness. If the springs are too tight, you will be wrestling with the pedal as you drive. Adjustment is as follows.
Firstly adjust the spring length. They should be 135mm end-to-end - that is from the point they hook over the nylon bushes to the point they hook into the small hooking plate lower down. Unfortunately adjustment is on the triangle at the bottom end but not difficult to do. The small triangular hooking plate can be wiggled and reset on different barbs on the vertical control rod to give you the necessary spring length. the spring tension holds the hooking plate in place.
Once happy with spring length adjustment, you can set the length of the vertical control rod.
Vertical Control Rod Adjustment
The top of the rod itself has a long thread. On my car, the mechanism has a long, shouldered adjustable rod (part 6 in the diagram above). this is threaded internally.
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| A long shouldered adjuster rod |
This forms an extension to the control rod and it's the adjuster rod that passes through the eye in the relay arm. A lock nut underneath the adjustable rod set its position on the control rod.
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| The extension arm passes through the relay eye |
When the pedal is operated, the vertical control rod and it's adjustable rod end are free to be pulled down through the eye on the horizontal control rod - but no so far that they disengage.
However later Ds have an arrangement where the long adjuster rod is not fitted and is replaced by a simple adjuster nut on the control rod thread.
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| Alternative adjuster on late Ds |
With no extending adjuster, presumably the control rods are longer so that they don't disengage from the eye? Mind you, with this arrangement there are also lock nuts on the top end of the rod - above the eye. On my car the rod is free to move within the eye, but it seems that with this arrangement those lock nuts if set so close to the eye) push the rod down - rather than the springs pull it?
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| Locking nuts on top of the rod |
Regardless, other than the fact that in this scenario it's the threaded rod that passes through the eye on the relay arm, the principles of adjustment are the same as it's the underside of the eye that is important.
Have a glamorous assistant fully depress the throttle pedal - or use two or three bricks. Fully open the carburettor butterfly. You can do this by rotating the horizontal relay arm attached to the carburettor with your finger so that its arm goes down.
Underneath that arm - more specifically under the eyelet piece that the vertical rod passes through - measure the gap between the shoulder of the adjustable rod and the underside of the eyelet piece.
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| With the pedal depressed and the butterfly open, there should be a gap here |
The gap needs to be between 1mm and 4mm. If it's not, slacken the lock nut and alter the adjustable sleeve on the thread of the rod by turning it. I presume it's the same for later Ds with an adjuster nut under there.
When happy with the gap under the eyelet, tighten the locking nuts of the adjuster rod and take whatever heavy weight you used off the throttle pedal.
That should be it!
