SELECTING THE BEST COMPONENT COMBINATIONS
CONRODS
The connecting rods (piston to crankshaft) are checked for straightness, and for cracking using a magnetic flux process. Gudgeon pins which locate the piston to the conrod (the ‘small end’, as opposed to the ‘big end’ at the crankshaft) are pressed out to remove the old pistons. Minor marks on the gudgeon pin can be honed out to remove the localised raised area without affecting the diameter, but larger marks would involve scrapping the complete conrod. The conrod’s big end (connecting to the crankshaft) can wear slightly oval on the face against which the bearing shell fits, in which case, the rod is scrapped. For special or rare engines where new conrods are not available, ACR can sometimes machine the mating faces between the conrod and the bearing cap, then re-bore the assembly, thus eliminating the wear.
CAMSHAFT
A new camshaft and bearing shells in the block are fitted as standard. Camshaft bearing housings are checked and sometimes found to have been machined oversize by the original manufacturer, in which case the block is scrapped. If they are found to be undersize, ACR will re-machine them.
PISTONS AND BORES
Although the cylinder liner bores and the pistons that fit in them are accurately machined, there are inevitable variations in finished sizes. We’re talking thousandths of millimetre here but, even so, if the piston sizes are matched to suit the bore sizes, we get a more efficient and balanced engine. So each of the eight bores and a batch of, say 20 pistons, is accurately measured and marked, so the best match of piston and bore can be achieved. Cylinder liners might also be further honed to achieve the ideal piston clearance.
CRANKSHAFT BEARINGS
Minute size variations also affect crankshaft bearing assembly where individual crank journals, accuracy of original line boring, bearing bores in the block and caps, and even the bearing shells, can cumulatively produce greater or less clearance. Thus, a crankshaft is selected to best suit the engine block’s bearing dimensions.
DOCUMENTED BUILD
All measurements are made in the same environmental temperature to avoid variances due to expansion and contraction, especially given that aluminium pistons will expand more than steel cylinder liners for the same temperature difference. On completion, all component sizes are permanently recorded on ACR’S build sheet for each engine.