Engine Builders Season Kicks in


<img width="205" height="150" class="floatleft" src="www.motorcycle.in.th/images/articles/Engine-Builders-Season-Kicks-in_1.jpg" alt="" />December to mid-March is the busiest time of year for engine builders, in preparation for the forthcoming racing season. Mee has ten engines to do in eight days. It's labor intensive as some4 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 six to eight times before they are right.

For one engine the cylinder block has been bored and hone4d to 800cc by an external service supplier. The bore diameters are all within three microns of each other, that is a very tight tolerance.

Mee 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.

Mee skims the cylinder block on his new-to-him Tecnodue SP330R skimming machine, he's not saying how much though; secrets are engine builders' stock in trade. The company invested in the machine so we doesn't lose time waiting for another company to do the work. Placing the block on the machine's bed, Mee 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 working out exactly what piston-to-cylinder head clearance he wants, so when the conrod stretches at full tilt, the piston will just kiss the head without catastrophically crashing into it.
With the crankshaft, pistons and rods in situ, Mee 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 camshaft 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 dial test indicator fixed to a magnetic base, it's fairly easy to find TDC. 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, Mee first measures when it is uppermost. 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 – in this case is was 21 degrees after TDC. Next he turns the engine over until the valve has been pressed fully open and is 1mm from closing, the wheel gives a reading of 47 degrees. To get the center-line of the cam lobe relative to the crankshaft he does the sum: 180+48=227-21=206/2=103. So the cam center 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. Mee 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 shaft of the cams don't turn, but the gears move around their slotted bolt holes with the bolt slack. Now the tightens the bolts.
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