It's easy to get at the choke assembly, there is one on each carb. The two screws are removed and the whole assembly pulls out, or falls out if the seals are really bad.
My seals were really bad, the top one seals the shaft of the choke to stop air getting in from the outside world, the bottom one should seal the other end of the shaft to make sure fuel is sucked in rather than air. It was doing absolutely nothing.
The old heads ready to come off, I noticed that the top of the middle two cylinders on this side where clean, indicating that coolant had ben getting in to the cylinders.
Repainted and tarted up a bit, it's a lot tidier than before I started, doesn't smoke now either, which is nice. I have added an overflow pipe for the radiator but it looks a bit pants, going to have to come up with something better.
Those of you that have been following my exploits will know that I hit a big problem the other week with my engine blowing blue smoke - something that would prevent me getting the thing registered. You may also remember that I had problems starting the car from cold, it could be a real bitch to start and something clearly needed to be done. Well, the time had come to sort both issues, the interior and so on would have to wait.
The carbs had to come off to sort the smoking problem so I looked at those first, I had a pretty good idea what was likely to be wrong as the car ran beautifully when hot - it had to be the choke circuits. When I first got the engine with the carbs I gave them a good clean and tried them out, as they seemed to work well I did not go the full rebuild route - SU parts are ridiculously expensive with a small packet of rubber seals costing 20 or 30 quid. I did not take the choke assemblies apart, that was my big mistake. When I did take them apart I found a missing gasket and perished rubber seals, two of which fell apart when I tried to remove them. On the SU's you have a rotating shaft that is hollow and has a hole in one side. That hole meets up with a jet when the choke is on, fuel is sucked through that, goes through the shaft and in to the venturi of the carb, thereby enrichening the mixture. If the assembly is not air tight instead of sucking fuel it just sucks air, which makes the mixture leaner rather than richer - the exact opposite of what you need. It was very clear that things were in a bad way and it was obvious that's where my problem was. Fortunately I had most of the seals I needed but I did have to make one gasket, which was easy enough as I had one I could copy. Everything was carefully cleaned, reassembled and then put to one side while I dealt with the smoking issue.
I had determined that the problem was my valve guides, when the engine was fully hot and the oil was at it's thinnest it was getting sucked in to the combustion chambers and causing the blue smoke. A compression test suggested it wasn't getting past the rings as compression was spot on for all 8 cylinders. I had a choice at this point, I could have fitted valve stem oil seals - Payen HR336 seals intended for an Opel Monza 3.0 fit and would have probably solved the problem. The other option was to fit later heads, some had o rings in the inlet valves, later ones had umbrella type seals on the inlets, the very latest have seals on the inlet and exhaust valves, basically they got modified as emission standards got more and more stringent. You only really need seals when the valve stems and guides start to wear and oil finds it's way between the two and in to the cylinders. Another advantage of the later heads is that they have slightly bigger valves and, more importantly, wasted inlet valve stems. Being a lot thinner they cause less restriction to inrushing gasses and allow the engine to breathe much better, particularly at higher revs, they should add between 10 and 15 BHP, a very useful increase. I thought that if I could find the right heads in good condition that would definitely be the way to go, the ones I found were a pair of ERC0216 units from an early 3.9 litre EFI Range Rover - perfect. They look like they had been rebuilt fairly recently and the seller told me they had come from a competition car that had been running well with no signs of smoke. They only needed a minor amount of cleaning before fitting, which is pretty easy on these engines but very time consuming, it took me a whole day to do it.
I used all new gaskets, a complete set was procured for 23 quid, an absolute bargain for a v8 engines, there are an awful lot of seals and gaskets in there. While it was apart I repainted the rocker covers to match the bodywork and polished up the carbs a bit, it looks a lot tidier now.
So the good news is that it now starts way better than ever before, the bad news is a really awful ticking sound from the front left hand side of the engine. I know what it is - it's the hydraulic tappets are not working correctly and so there is no pre load, which is causing tappet rattle. On traditional tappets you have a bit of clearance when cold so that when the engine is hot you don't get valves cracking open where the push rods have expanded, you don't have clearance on hydraulic tappets, the rockers should always be in contact with the vale stem, oil pressure keeps them there. Why this has started now is a bit of a mystery, I will investigate today and see what happens, my suspicion is that when I was messing about I changed the oil pressure relief spring as my oil pressure seemed too high. I am wondering if my gauge was telling lies and I now have less pressure than I thought - that could definitely cause the issue. The other thing it could be is that the valves are not shutting properly, I doubt that one as I tested them by filling the combustion chambers with petrol and seeing if there was any leakage- there wasn't.
The good news is there was no smoke whatsoever and the engine ran really well, if I can sort out this latest problem it's good to go.
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