Typical clearance between piston and bore is 28 ... 07) a gSX-r750 K3 after
boring it out to 800cc. ... after that, fitting the clutch and engine covers is child's
play.
big-bang
g n i d l i u b e n i g n e -steps the de si ly at ne ch oa pr ap l ca di ho A met ad stripping re th e as kc an cr of at re th g in worry Game Words Olly Crick Photography Rory
J
anuary to March is the busiest time of year for engine builders, in preparation for the forthcoming racing season. Tim has nine engines besides ours to do in eight days. It’s labour intensive as some parts have to be assembled, stripped back down, then measured before being assembled again. Cylinder heads sometimes have to be torqued down onto the cylinder block and then disassembled half a dozen times before they are right. Our cylinder block has been bored and honed to 800cc by Perfect Bore. The bore diameters are all within three microns of each other (0.003mm), a tight tolerance. Tim has balanced the pistons and rods on scales, removing parts of the pistons’ skirts to achieve perfect balance. The pistons have then been matched to the bores, the largest piston going in the largest hole and so on. Typical clearance between piston and bore is 28 microns all round. Tim skims the cylinder block on his newto-him Tecnodue SP330R skimming machine, he’s not saying how much though; secrets are engine builders’ stock in trade. He’s invested in the machine so he doesn’t have to lose time waiting for another company to do the work. Placing the block on the machine’s bed, he measures that it’s sitting squarely by lightly touching the surface to be machined with the cutting tool. Three corners need propping up with a single sheet of paper to make it absolutely right. He’s worked out exactly what piston-to-cylinder head clearance he wants (fractions of a millimetre, but again he’s not saying), so when the conrod stretches at full tilt, the piston will just kiss the head without catastrophically crashing into it.
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Project Big-Bang pt3
Building Big-Bang
1 Block bored to 800cc. 2 TR and OC peer into the Tecnodue skimming machine. It skims with cutters and grinding stones. The stones are used when valve seats need some material removed. The seats are proper hard and would ruin the cutter tip. ‘It would be like finding a bolt in butter,’ says Tim. 3 The skimmed block is washed in a Safety Kleen parts washer at 60°C for 10 minutes before re-assembly. These car heads give a before and after comparison. 4 Conrod cap bolts are designed to stretch as they are torqued, use them once and throw away. The procedure for tightening ours down is torque to 11lb-ft, followed by an extra 90° turn. Here Tim’s marking the position with a gold pen ready for the final turn. 2
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With the crankshaft, pistons and rods in situ, Tim uses plasticine to stick a strand of soft solder to the tops of the pistons, front and back. Then he torques the head and gasket down. Next, with a spanner on the crankshaft, he turns the engine over, crushing the solder between the pistons and cylinder head. Removing the cylinder head, he then measures the solder’s thickness to check his piston/cylinder head clearance calculations are correct. With clearances sorted, the head can be refitted, the camshafts put in and shimmed for their correct valve clearances. With a suitable tool passing through the cylinder head and resting on a piston top and a DTI (dial test indicator) fixed to a magnetic base, it’s fairly easy to find TDC (top dead centre). A degree wheel is bolted onto the crankshaft with a suitable pointer reading TDC on the wheel. To dial-in the cams, with the indicator now set on one of the inlet valve buckets, Tim first measures when it is uppermost (valve closed). He then turns the engine clockwise from the right-hand side, the way the engine normally rotates, with a spanner until the bucket moves down 1mm and notes the angle on the wheel – ours was 21 degrees after TDC. Next he turns the engine over until the valve has been pressed fully open and is 1mm from closed, the wheel gives a reading of 47 degrees. To get the centre-line of the cam lobe relative to the crankshaft he does the sum: 180+47=227-21=206/2=103. So the cam centre line is set at 103 degrees, the position of the camshaft relative to the crankshaft. It is stated as the number of degrees that full lift occurs after TDC for inlet and before TDC for the exhaust. Tim is reluctant to say what his preferred cam settings are, but they are adjusted from this point using the bolted-on cam gears. He slackens off the bolts and turns the crankshaft by his preferred adjustment. The shafts of the cams don’t turn, but the gears move around their slotted bolt holes with the bolts slack. Now he tightens the bolts. Job done. See www.pipercams. co.uk and click on Technical advice for a more in-depth explanation. After that, fitting the clutch and engine covers is child’s play. OC
BANG !
Finished engine is now ready for testing at Mallory Park. The excitement is tangible
What are we doing?
In essence, chasing traction. We’re ‘BB2’ big-banging (see PB, January 07) a GSX-R750 K3 after boring it out to 800cc. Then we’ll re-strip it and turning it into a ‘BB3’. Kawasaki used these configurations (plus others) during their 2006 MotoGP campaign.
Who’s doing it?
Tim Radley. Proprietor of Gloucester-based Race Developments, a Dynojetapproved tuning centre. Tim has been building and tuning engines for race bikes for 20 years.
Targets
We datalogged the K3 around Mallory Park before working on it, taking acceleration figures out of three corners – Gerrards, Edwina’s and exiting the Bus Stop into Devil’s Elbow. The figures were published in PB January 2007 and they are our baseline numbers to measure our new engine configurations against. In addition to that the K3 had a peak torque figure of 59lb-ft@10,200rpm and a peak power figure of 133bhp@12,500rpm.
Next month: Big-Bang runs. Maybe
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