AEC V8 Engine Restoration - Part Two.
(Part one is several pages back now, if anyone lands here and is looking for it).
In this part we will cover the cylinder heads.
The original heads from engine 316 were chemically cleaned inside and out at the same time as the block, and were sent over to Ivor Searle of Soham for reconditioning and hot pressure testing. Hot pressure testing involves sealing off all the water ports, immersing the head into a tank of hot water at normal engine running temperature, and applying air pressure to the water channels in the head so that any leaks can be seen as bubbles. After a couple of weeks I got the call I’d been dreading - your heads are both cracked.
I went over to Soham to see for myself and plan the way forward, but the news was not good. One head had failed the hot pressure test catastrophically, with bubbles coming from deep within an exhaust port - probably due to the ‘hot spot’ cracking mentioned earlier in the thread, where the coolant boils within the head, forms a steam pocket allowing the iron to dramatically heat up, then gets cooled suddenly when the coolant begins to flow again as the RPM of the water pump increases. This particular head was scrap, no feasible repair could be done with the crack being located so deep in the port. The other head had failed it’s hot pressure test too, this time leaking around two of the injector sleeves, but with a set of dummy injectors fitted and torqued down, it was re-tested and passed with no leaks.
At this time the second head was due to be refaced by Searles, and was showing clear cracks between the injector hole and the valve seats. As those with experience of direct injection Diesel engines will know, this type of cracking is very very common, and although never ideal it is often not a cause of great concern if it is considered minor. As these cracks were not leaking under pressure when hot, it was all of our thinking that they would not be an issue - but I was far from happy to leave it as I was striving to create as close to a new engine as possible…
The search was now on for pair of replacement heads, no easy task with an engine as rare as an AEC V8. They had to be AV740 heads too, as the AV800 heads have bigger valves to suit the larger bore size that will not clear the top edge of the AV740 liners. A lucky break (or so it seemed) came in the form of a pair of heads from a former AEC V8 owner who had acquired what he believed to be a pair of brand new unused AV740 heads as spares for his engine. These were bought and stripped down, during which it became very obvious that they had been at least run on an engine due to the presence of carbon in the ports. These heads were sent off for chemical cleaning, as before…
It was then back to Soham for another round of hot pressure testing with everything crossable crossed!. But to no avail - I got another phone call to say that one of the replacement pair of heads had a catastrophic crack into one of the oil galleries. This really was a double blow, the heads had been bought as new items, but clearly were not, and on top of that one was cracked!. I got a real sense at this point that patience was wearing very thin at Searles with me and my seemingly endless stream of unserviceable engine parts, so I collected everything up and took time to collect thoughts on a way forward.
I now had four heads, and with them all on the bench one day noticed something quite interesting. The original heads from engine 316 were marked with a cast ‘A’ between the centre valve guides, one of the replacements was similarly marked, but the other was marked ‘A1’. On studying them all, the ‘A1’ head had some obvious modifications to the casting compared to the other three, and it was this head which had passed the last hot pressure test. At this point in the project I was really lucky to find a guy called Simon Smart who runs Automotive Services in Northampton, a firm specialising in reconditioning all types of engine components. I should perhaps point out that the Northampton area is great for finding really good engine machine shops and the like because of it’s proximity to Silverstone and the motorsport businesses based there - something which would benefit this AEC V8 project more than once over it’s course.
Simon took a genuine interest in the V8, not least because he knew AEC’s from his fathers time as a lorry driver for London Brick in the 60’s and 70’s. Simon re-tested all four heads, and reached the same conclusion as Searles, the ‘A1’ head had passed the hot pressure test with no issues at all, and one of the original ‘A’ heads had passed, but had the minor face cracking. The search was now on again to try to find yet another head to make a perfect pair for engine 316. A worldwide search proved fruitless, but eventually a complete engine was located which had allegedly been rebuilt by AEC at some point in it’s life. This engine was bought, stripped and noted to have one head marked ‘A1’, and another head marked ‘A2’ - with even further casting modifications!..
Now the thing we must recognise here is that engine 316 was built very late in 1969, and was one of the last AV740 engines built before sales of the AEC Mandator V8 were suspended. The fact that improved ‘A1’ and ‘A2’ marked heads were produced after the ‘A’ marked heads originally fitted to engine 316 proves that AEC were still working to get some of the V8’s reliability issues addressed even after production had stopped, something I don’t think has ever been credited to them.
The most recently acquired pair of heads were again chemically cleaned and then sent off to Simon, and this time both passed the hot pressure test, and both had no face cracking - so after six cylinder heads at last we had a perfect pair, and even a spare!. Simon selected the very best pair dimensionally and set about fully reconditioning them with a face re-grind, re-cut valve seats, brand new old stock valves and new metric valve guides which he actually managed to cross reference from a Rolls Royce application.
The heads were now fully sorted and ready to go, so it was time to look at the crankshaft, pistons and camshaft - in the next instalment!.
