Cranking over
Matt installs vital internal components in the TR engine
With the TR’S engine block thoroughly cleaned and fitted with fresh oilway bungs (PC, June 2018) it was time to start putting the freshlymachined rotating internals back in. First up was the crankshaft – the original – which had only required minor remedial work at Ivor Searle Ltd (PC, May 2018) and been ground down to first undersize, meaning +10thou main bearings were to be used during the rebuild process. The crank journals had also been lapped and polished for good measure.
With the block inverted on an engine stand and under the watchful eye of the ever-patient (despite my occasional boo-boo) Jason Wright of TRGB, I fitted the top half of the big end bearings and gently slotted the shiny crank into place. Beginning with main bearing No.1 I then placed a strip of Plastigauge onto each crank journal. For those who don’t know (as I didn’t) Plastigauge is a must for any engine builder, is used for measuring clearances and is comprised of a rod or thread of a compliant plastic material of accurately determined cross-section – either circular or square. Firstly, the surfaces between which measurement is to be made are separated. Plastigauge is then inserted and the
surfaces are returned to their standard position. The once circular (or square) section will have been flattened but the area of the cross-section will remain unchanged. Thus the clearance to be measured is equal to a constant divided by the width of the strip after deformation.
By opening the surfaces to reveal the deformed gauge, width can be measured directly and from this the clearance can be determined. In practice, the need for any calculation is averted by the use of a calibrated scale on which an array of marks has been printed (see picture on p103). After applying plenty of graphogen assembly