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As Featured in Thoroughbred and Classic Cars magazine - March 2001 Issue

A stitch in time

Surelock can literally stitch your engine back together if it blows.

If you race an historic car you put ancient components under great stress, and it's not unheard of for con-rods to make a bid for freedom through the side wall of your engine block. Or say you're restoring a rare car that's stood unloved for years, and its cylinder head has cracked through frost damage. Replacement can be difficult and expensive. So where would you go to have the original repaired? America? Italy? How about a one-man operation in a tiny workshop in England's oldest county: Rutland.

'I've got a truly international clientele,' says Nick Hood, proprietor of Oakham-based cold-metal stitching specialist Surelock. 'What I do here is a dying art. People can't easily get something like this properly repaired anywhere else.' He points to a Delage engine block with a quarter-inch wide fracture stretching almost the whole length of its outer wall.

The way you might expect to repair a crack in an iron casting is by welding, but Surelock's method is entirely mechanical and involves no heat. Nick explains: 'Welding involves pre-heating a block or cylinder head to 600 degrees celsius and, while it will repair the crack, it will also distort bores, block oilways, ruin coolant channels and destroy bearing journals. What you're left with will need a great deal of machining to make good. Cold metal stitching simply heals the fracture and leaves everything else alone.'

The process involves drilling a line of holes through a template across the crack at right angles to it, and then knocking out the webs between the holes. This creates a caterpillar-shaped channel, into which specially-made nickel alloy rods - 'locks', as Nick calls them - perfectly fit. The process is repeated at intervals along the fracture, and the gaps between the locks drilled and tapped to accept bolts. Nick then tightens in the bolts, chisels off the bolt heads flush with the parent metal, and cross-peens the locks and bolt-shafts until the fissure is completely filled.

An absolute seal is achieved by further smooth-peening and then the whole assembly is pressure-tested to three times its usual working limit. The finished result literally looks like a row of stitching, but is imperceptible to the touch. Says Nick: 'You can paint a block after it's been repaired and nobody would ever know, but many owners leave the repair undisguised. Each one tells its own story.'

Holes are treated by cutting out the affected area and patching in new metal, fixing the join exactly the same way as stitching a crack. The technique is equally suitable for cast iron or aluminium alloy.

'I've got a real variety of work at the moment, from Rolls-Royce 20hp cylinder heads to blocks from a Vintage Renault and De Dion to MG T-type and racing Talbot,' says Nick. 'As a guide, I could repair cracks around the valve seats of an Austin-Healey 3000 for £250, or stitch a six-inch block fracture for £300. And I'm not tied to the workshop permanently. Some repairs can be done in-situ. I've repaired a crack in the block of a Singer Le Mans without even removing the engine. That cuts down the cost of stripping down and rebuilding.'

Surelock was founded more than 40 years ago by Nick's father, Bev, and employed 14 people at its peak, when the company's repair techniques were employed in many industrial applications. Nick learned his skills from Bev and took over in 1991, scaling down the operation to specialise in repairing historic racing car engines. He's also completed many other projects, including the counterweights for a flood barrier, which had sheered.

One particularly memorable job was two years ago. 'We had an Osca racing car in, just been rebuilt, and the restorers had blown the engine during testing. It was due to take part in a parade lap at Le Mans. At the last minute, we stitched it and they rebuilt it. Its owner drove it straight down to Le Mans, took it round the circuit and drove it all the way home again. It never skipped a beat.'

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