||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
'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
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
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.
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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