Oooooookay, I was a little unsure whether to revive this thread or let sleeping dogs lie, but I have learned a lot more about my engine in the last couple of weeks, and for the most part I am very satisfied with the overall package, so I wanted to give credit where it is due.
First up, I invited an engine-builder friend over to have a look at what I had. I popped off the cam covers on both engines and he immediately pointed out that the Alfatune cams had been re-ground for a longer duration. I hadn't noticed before (duh), but the lobes were considerably less pointy than standard, and to maintain the same amount of valve lift, the base circle had been machined down as well...
Initially I also thought that the tappet buckets had run out of adjustment as well, as there is usually a couple of threads visible on the centre grub screws, but now that I think about it, they have to be that low so that they don't hit the camshaft (due to the reduced base circle diameter).
So, I am not sure what valve adjustment range is available to use, but with such limited clearance under the camshaft the grub screws have to be that low... On to other things
The engine block is from a 1.5 twin carb
, as I was told. Type number is AS 301.28, same as my 1.5 Ti. Block casting code is 18E79, which I think might be a date code (18/05/1979 perhaps? My later 1.5 Ti has a block casting code of 25B80, which suggests 25/02/1980, and the serial numbers are consistent with this, the Alfatune block being only a couple of thousand units in, the Ti engine 21,000 units later).
I tried to measure the stroke through the spark plug hole and came out with more than 73mm (1.7 crank), but the angles were a bit off and the pistons have standard concave depressions in them, which may also have made a difference. The pistons have a reference code starting with "84" stamped on them, so it looks like the bores are standard for the 1500. The actual stroke measurement came out at 77mm
So I am still a bit uncertain of the specification, but it seems pretty certain that the Alfatune has a crank from a 1.7 at the very least, maybe bigger! I was told the capacity was 1600cc though, which with standard 84mm bores can be achieved with the 73mm stroke from a 1.7 crank.
So the Alfatune is shaping up to be an impressive engine, just as I hoped it would be. There is just one thing that I am not happy with, and that is the camshaft belt clearance. Maybe it is OK for a couple of races, but for street use, I just can't get over how close the belt runs to the water pump...
Moderate finger pressure is all that is needed to put the belt into contact with the pump body. If I was to remove sufficient material from the water pump to give adequate clearance (say 5mm or so) I would risk breaking into water, or at the very least a fractured casting somewhere down the line.
On top of my concerns about the belt clearance, there is the issue of the tensioners. You can see from the pictures below how much further the tensioners on the Alfatune have to rotate compared to the standard motor. This reduces the spring tension to the point where you may as well remove the springs altogether, and use a different method the pre-load the tensioners.
Now these are just observations, not criticism. I am looking to use this engine primarily on the street, so I have a different set of priorities to a circuit racer. What I would like to do is increase the belt tension by spacing the camboxes away from the cylinder head using aluminium shims 1mm thick. I am drawing up the shape of these shims using the thin plastic gasket as a guide (I'm hoping to get them cut by water-jet). Because the valve stems will be 1mm further away from the tappet buckets I intend to use "top hat" valve stem shims of 1mm thickness to restore the valve clearance. These shims are available from Classic Alfa for 750 series Giuliettas (which had 8mm valve stems like the Alfasud), and are also used on certain Ducati motorbikes. Of course I will have to use vernier pulleys instead of the standard ones, but with this approach I recover nearly all of the running clearance around the camshaft belt AND the tensioner springs will be effective once again, so I can change the camshaft belts using standard factory procedure and no modifications are required to "consumables", such as the water pump.
Not the simplest or cheapest solution perhaps, but I think this is the best way to go for optimum reliability on the street.
I will let you know how things go.