Hello Jon,
I'd better order myself some rocker cover gaskets and the check the valve seals. In the mean time I lengthened the rod on the accelerator linkage to give as much free play as possible. This helped a bit but you have to press the linkage home by hand to get the revs down far enough. Obviously there is sufficient travel there but it won't do it on its own. I'll investigate further this weekend and report back.
Thanks very much for your time and knowledge, regards Mike.

 

If you pop the air filters off, then watch the butterflies when you push the throttle linkage closed and see if they move at all.

If they do make sure all the linkages are not pulling the throttle open slightly. The linkage on the V8 is particularly complicated, each of the mixture control rods should be exactly the same length, and operate on exactly the same arc otherwise one carb will open more than the other. When you check the butterflies for movement, if one move slightly but not the other, lengthen that mixture control rod so they are both the same and see if that helps.

After that you are down to adjusting the fast idle screws, but rule out everything else first so you don't throw the carbs out and have to start over.

 

Hello Jon,
I followed you advice and checked the butterflies and they both looked to be fully closed when the throttle was relaxed. I moved on to the idle screws turning them both down to the stop. I then backed them off equally until the revs hit 600rpm(about one and a half turns) . This seems to have sorted the problem and now I can select drive and reverse without the clunk as before.
This was just a garage test so the engine probably wasn't up to full temperature (the gauge isn't working) hopefully I'll road test it soon to give it a proper test.
I'm sending off for the rocker cover gaskets now and a set of spark plug tube seals as some of these are leaking. Thanks again for your advice. I've attached a picture of the car, it was re sprayed in 2005 and still looks fresh.
Regards Mike
PS The front seat leather is something else that needs attention, is this what they call wedgewood blue?

 

The V8 doesn't have valve guide seals.

 

Hello Chris,
What I meant was 'valve stem seals' sorry for any confusion. Mike

 

SNG list them part No. 2A879 ?

 

Well then, I'm confused. My parts manual doesn't show or list them and the Daimler forum guys say it doesn't have them. I know there is a modification that can be done to fit them so that may be the SNG part, but that's only a guess.

 

I looked into this further, SNG don't show it as a modified part, however other sites do seem to indicate it's for a modified valve guide, but I also found a post on the JEC forum from 2007 when a guy changed his in situ, so they must have been on his before that date, but that's not to say they weren't modified earlier.

Jaguar fitted them to the straight 6 on later engines, my 1966 engine had them.

So you may well be correct, that makes Mike's issue slightly more complicated.

Mike, you can check to see if they are fitted as per previous posts, if they are not fitted, your issue could be worn valve guides, but this will be more awkward to prove with the heads in situ, you would have to remove the rocker gear, remove the spring as before, then holding onto the valve stem, remove the compressed air, so you can slightly lower the valve and waggle it to check for wear, then reapply the compressed air without dropping the valve. If you get the piston on TDC first then if you do drop the valve stem, you won't loose the valve down the cylinder !

If there is wear on the valve guides, then it's a head off job to get them replaced.

 

Hello again,
I removed the offside rocker cover today to check the stem seals. They seem to be made of a whiteish plastic/nylon type material . The ones I probed with a screw driver were soft and pliable so hopefully the others will be the same.
I'm not experienced with these engines but is it possible for oil that has leaked into the spark plug tubes to somehow find its way into the cylinders? Starting to grasp at straws now.
Regards Mike

 

Hi Mike, can you post a pic of the seals, I have never seen white ones, they are generally black with a spring around the top edge to help squeeze the seal to the valve.

It would be almost impossible for the oil to get into the cylinders from past the spark plugs without a lot of hissing when the engine is running as the gasses pass the spark plugs the opposite way !

 

Hello Jon,
I've taken some pictures for you, looking at them today in daylight rather than a lamp they look more grey than white. There is definitely some kind of flexible collar inside the spring.
I managed to buy an old service manual today so that should be a help.
Regards Mike