AEC V8 Engine Restoration - Part Three.
(Part two is on page 33, if anyone lands here and is looking for it).
Now seems a good time in proceedings to look at the next phase of the engine restoration.
Some of the following illustrations are from the AEC V8 service training course, hosted at the BL service training centre at Standard Triumph, Radford.
We have just been discussing power ratings and power delivery, and this is one area where the AEC V8 engine did actually get a good deal of innovative development in the early stages of it’s conception. It had an exceptional power output for it’s time, ably described by every lorry driver lucky enough to drive a Mandator V8 in service.
But why?.
There are a couple of key paragraphs in the three-page CM article that I posted a few pages back, the first is…
So how was that possible?.
The first key to this was AEC being among the direct injection engine manufacturers of the early 1960’s to employ Toroidal Cavity pistons and masked inlet valves. In basic terms, the Toroidal combustion chamber in the piston top improves the way in which air and injected fuel mix, and therefore burn more intensely, releasing more power from the process, also improving efficiency. (If anyone can describe it better, please do!)
The overall combustion process itself is the key thing that engine development engineers are always trying to improve, and one of many ways of doing that was by masking the inlet valves. The mask is a small curved section of the inlet valve head that protrudes up into the port.
You can see it on valve ‘B’ here…
This mask has the effect of inducing turbulence or ‘swirl’ to the air being drawn into the cylinder on the induction stroke, allowing more air to enter the cylinder and again giving an improved mix ratio for the compression to ignite once the atomised fuel is injected.
I’m trying to keep this simple, honest!.
For this to work, the inlet valve cannot be allowed to rotate in the way that a valve normally can in an engine, so the stem of the valve is splined and a special cap is fitted to the top of the valve guide to keep the valve mask in exactly the right position to achieve the best possible combustion results. This can be seen here…
I was lucky with engine 316 because I had actually managed to find new old stock valves, so this was one area of the engine that didn’t cause me great problems, but of course it couldn’t last, and the next component in line was a major headache - the camshaft.
By this time, during the course of this restoration, we had stripped down four AEC V8 engines, one of which was an original low mileage unit. The original camshaft in engine 316 was in horrendous condition, out of the 16 cams only 4 still had the ends of the lobes intact. The others all had wear up to 6 mm - a colossal amount for a cam lobe tip to loose, obviously well through the case hardening.
We looked at the cams in the other engines, but they were ALL worn, even the low mileage one, although to a much lesser degree. The cam followers were the same, where the lobes had worn down, the associated followers were all badly grooved as shown here…
But why?.
The conclusion was that the followers are designed to rotate, thus spreading the wear evenly across the contact surface, but it was obvious that most of the followers in all of these AEC V8 engines hadn’t been rotating at all, which was very confusing. So we now had a major problem. I couldn’t put 16 serviceable cam followers together from 64 recovered from all the stripped engines, and I had no good camshaft. Bearing in mind that British Leyland had withdrawn spares support for the AEC V8 engine completely by 1976, I stood no chance of finding new parts. I made a call to Simon Smart at Automotive Services in Northampton to see if he had any ideas, and luckily he did!. “Bring me your best parts” he said, so over I went with the 24 best cam followers and the 2 best camshafts.
After a lot of surface testing and measuring, the best followers were selected to be reground, and the best camshaft sent off to Kent Cams for re-grinding. Now, anyone who has had a Ford car in their youth is probably aware of Kent Cams from their connection to motorsport, but up until this point I didn’t realise that they are one of the few UK firms that specialise in ALL engine camshaft’s, whatever the application.
I had two questions - what would this all cost?, and how can you grind material OFF a worn cam to restore the original lift?.
The first answer was encouraging. “As it’s a 1960’s Diesel engine, both inlet and exhaust cam profiles will be identical” they said. “And if we’ve got a known master profile on the shelf, you are just looking at the machining and re-hardening costs, so circa a couple of hundred quid”.
All good so far.
The second answer was rather obvious when you think about it. Grinding material off the BACK of the cam enables the material at the front to be profiled back to completely the original shape, with no detriment at all - as long as there is sufficient unworn material left on the cam, and ample adjustment on the rocker arm valve clearance adjustment screws to take up the difference, which there easily was.
Then I got the usual AEC V8 phone call.
It was Kent Cams.
“There is a problem with this camshaft”.
They had done a lobe profile analysis on the cams with no wear, and found two things of interest. The inlet cam profile was very different to the exhaust, and neither profile matched ANY of the hundreds of master profiles used for grinding held in their huge library!.
Great.
The clue to this was actually in the CM launch article…
So now I was faced with the increased cost of having TWO master profiles specially made for the grinding machine, just to get one camshaft re-ground!.
That’s AEC V8’s for you.
Kent Cams did come through though, and a fully reconditioned camshaft and followers (including some spares) duly arrived back with me…
The other thing Kent Cams said was that, contrary to modern practice, the tips of the AEC cam lobe were straight - ie parallel to the shaft.
Now I thought all cams were made like that, but apparently not. Cam tips these days have a very slight taper of only a few thou machined into them, which mates with a very slightly concave surface on the follower. The two are then positioned slightly off-centre to each other to promote the follower to turn every time the cam strikes it.
In the AEC V8 engine the followers are all completely flat, the cam tips are parallel to the camshaft, and the cam strikes the follower at exactly the centre point. Other AEC engines have the flat cam tips and flat followers, but do have the two off-set slightly to promote rotation.
So why build an engine like that, knowing full well that the follower would not turn at all if just a little sticky oil or carbon got near it?.
The answer actually came from Perkins.
“That was quite normal when we were working on development engines in the 1960’s, trying different cam profiles and testing prototypes…” they said!.
So, all the hard development work had been done on the innovative cam profiles early in the AEC V8 development, but when the project was shelved, the finer detail of the cam and follower relative positioning still hadn’t been finalised.
If details like that had been allowed through before production started, what else would we find?.
One thing was quite shocking really.
Positioned over the top of the cam followers is a retainer plate with holes for the push rods to pass through, shown here…
The idea is that it acts as an oil baffle, and stops the followers from being pulled out by suction if the push rods are removed. In the prototype engine that I stripped, the push rod holes in this plate were all in slightly the wrong place, and had all been hand filed to an oval shape to clear the push rods.
When we looked in all of the production engines, the push rods were actually rubbing on it!.
In two engines we even found that the push rods were in fact bent, and would pass through the centre of the hole, but when rotated would lay against one side of it.
Can you imagine this?. An engine in production with such basic things yet to be sorted out.
What must the people assembling them have thought?.
Why was it not addressed?.
Keith Roberts and his team must have stood in complete disbelief at Southall watching machine tools being set up to produce an engine with such fundamental simple flaws still in it’s design, let alone the major issues that they knew it still had.
I don’t really like to speculate, but to me it is just as though a production set up team had burst into the AEC R&D department, taken all the prototype V8 files and drawings away, and began tooling up to manufacture the engine - whatever the R&D team said in protest!.