DIRTY STUFF

IHATE it when they arrive with all the bits of an engine in boxes. This guy wanted a go-faster engine for his rally car, a Mk1 1500 Ford Cortina. So he ripped a spare engine apart, and to save on the dollars, he got a lot of the machining done to suit the parts he had picked up at swap meets. These included valves and bearings and a duplex timing chain conversion kit, plus four .060in-oversize pistons. The latter were pre-loved pieces, slightly scuffed on the skirts, with no names anywhere. I had seen these anonymous parts before; they were rough cast and machined but of a reasonable quality.

Anyway, before he got to me, he’d had the crank ground and the block bored to suit these pistons and found a guaranteedgood Cosworth camshaft, a set of Titan roller rockers, a flash high-top alloy rocker cover, and a new high-volume oil pump with a canister filter. All good stuff, he reckoned, and could I put it together for him?

So I agreed to help this guy out if he could give me a month. At least all the bits were clean. Somebody had got at the cylinder head at some stage, opening up the ports and milling a big chunk off the head face. When I measured the combustion chambers, that old engine was somehow running at over 12:1 compression. As the rally man had also got hold of a set of lightweight, oversize stainless valves with 7mm stems, I knew I would have to get the head fitted with custom bronze valve guides to take these, along with opening out the chambers and cutting new, larger seats.

When all this was done, without facing the head deck, the comp ratio dropped down to a whisker over 10:1, which would be quite okay as long as the bloke ran the built engine on PULP. To control the long-duration, highlift Cosworth A6 camshaft, which is about as big as you can get for these engines, I used a set of Us-made duplex coil springs, way larger than the original Ford pieces and needing bigger spring seats cut into the top of the head. I knew these parts were good for 11,000rpm with an A6 ’shaft before spring surge, which occurs when valve heads are really close to piston crowns.

So I got all that done and began the build by slotting in that Cosworth camshaft. As Ford’s original cam drive was by a single-row chain, which is too weak for big cams and springs, uprating these engines requires the fitting of a duplex chain drive – or with the extreme revvers, special triple gears. The customer was going to run a set of Ford twin-cam rods, which are heavier and good for 8000rpm, but as they were used pieces, I reckoned they would be safe to 7500 revolutions.

I had managed to pick up a set of Repco rings and lead-indium main and big-end bearings through luck and knowing the right people, so I fitted them to the conrod and piston assemblies and got ready to pop them into each cylinder.

Didn’t get very far. I wound a good ring compressor onto number one, started that assembly into the cylinder with the crank throw at the bottom, gave it a couple of taps with the wooden end of a hammer and it stopped. So I unwound the ring compressor; the three-piece oil and second ring had gone in, but the top ring seemed to have popped out and stopped the piston going any further. Tried again – same result.

Further investigation revealed that the top ring groove in those no-name pistons was too shallow, so the ring couldn’t compress – like a true idiot, I hadn’t bothered to check. It was only half a millimetre short, but that was enough to stop all work.

So, once I get the pistons back from the machine shop and fit them into the four holes in the block, the next step is to degree-in the cam with a degree wheel mounted on the nose of the crank and a dial indicator checking piston height. Cam timing should be 55/86-86/55 with a .400in lift, depending on the ratio of those Titan roller rockers. With all that and a couple of 45mm dualthroat side-draught Weber carbs, I reckon that even with the nameless pistons, this mill should pump out close to 140hp!

THE TOP RING GROOVE IN THOSE NO-NAME PISTONS WAS TOO SHALLOW, SO THE RING COULDN’T COMPRESS – LIKE A TRUE IDIOT, I HADN’T BOTHERED TO CHECK