To Optimise Performance...
... I thought it might be wise to weigh the pistons and conrods before assembling the engine. But before I got that far, the pistons which had been sitting around for a number of years, needed some attention and the gudgeon pins removing.
Half an hour in the oven set to 100° did the trick and all but one pin, which was in the early stages of amalgamating with the casting, popped out with ease. The next operation was one I never look forward to, putting the rings on. But, with patience and a steady hand, all went well, and none broke.
However, I realised that I didn't have enough oil control rings to go round - I was 4 short. Getting another 4 +.020" rings was going to be a long shot so I consulted with the ever-resourceful Holmes, and had his thoughts confirmed by a second opinion from Learned Counsel. The long and short of it was that the original pistons had only 3 rings - first, second and a scraper ring - and it was only the after-market pistons that introduced a second oil control ring to help with worn bores. Holmes also reminded me that Rootes Group supplied the Humber Hawk with four-ring pistons but omitted the fourth ring, adding it only later in servicing when oil consumption became excessive. With newly bored bores - so to speak - that's the plan.
All six pistons weighed in within 20 grams of each other, despite two of the gudgeon pins being of slightly different design with more material in the bore. In fact, it was two of the four of the same design that were the farthest out.
I wondered if weighing each conrod and piston together would be a good idea but having each assembly within two or three grams of each other is not the same as having each of the components separately within that tolerance. In the small hours, I could see the forces acting on the assembly, but couldn't begin to explain it to myself - it just didn't feel right. Before I weigh the conrods, I'll have to turn up new small ends.
You may recall that the top of the block had signs of corrosion which was more than just surface rust. I whizzed it down to the engine shop where it was popped on the surface grinder. After several passes, 4 thou was removed.
Mmmm... shiny! In the cylinder above the block is an arrangement of grinding stones that do the business. A highly geared wheel on the side of the machine adjusts the height of the cylinder in tiny increments per turn.
Leon made up this plate to get the valve timing on his Coventry Climax exactly where he wanted it. Setting the lift on No.1 inlet valve (including the specified tappet clearance) to suit the new hairy cam is achieved by turning the camshaft with the cam chain removed. With that set, No.1 piston is brought up to TDC and the sprocket secured.
It sounds simple, but it's probably a bit of a performance.