Crankshaft Main Bearing/Journal Checking, Measuring and Bearing Selection

Minor differences in crankshaft dimensions are compensated for by using selective bearings. For further information on bearing part number to colour cross-references, see the latest parts information.

note
All dimensions in millimetres.
caution
Always confirm, using the Plastigauge method, that the running clearance is correct before final assembly. Severe engine damage could result from incorrect clearance.

Crankshaft Main Bearing/Journal Wear

Minor differences in crankshaft and crankcase dimensions are compensated for by using selective bearings. For further information on bearing part number to colour cross-references, see the latest parts catalogue information.

  1. Measure the bearing to crankshaft journal clearance as follows:
  2. Measure the bearing to crankshaft main journal clearance using Plastigauge (Triumph part number 3880150-T0301).
    3. note
    Do not turn the connecting rods and crankshaft during the clearance measurement as this will damage the Plastigauge.
  3. Separate the crankcase halves (see Crankcases - Disassembly).
  4. Wipe the exposed areas of the crankshaft journal, and the bearing faces inside the crankcase halves.
  5. Apply a thin smear of grease to the journal and a small quantity of silicone release agent to the bearing.
  6. Trim a length of the Plastigauge to fit across the crankshaft journal.
  7. Fit the Plastigauge to the journal using the grease to hold the strip in place.
    8. note
    The original fixings may be reused for bearing selection. Do not use new fixings as they may only be used once, even if the single use is related to bearing selection.
  8. Lubricate the threads and the face of the fixings with molybdenum disulphide grease.
    9. note
    It is not necessary to apply silicone sealer to the crankcase mating faces during the bearing selection process.Only apply silicone sealer during final assembly.
  9. Refit the crankcase and tighten the original fixings (see Crankcases - Assembly).
  10. Release the fixings and remove the crankcase.
  11. Using the Plastigauge kit, measure the width of the compressed Plastigauge.
    12. Graphic from Connecting Rod Bearing Selection (gagc.svg)

    Checking Crankshaft Journal Clearance using Plastigauge

  12. For specifications refer toCrankshaft.
  13. If the clearance exceeds the service limit, measure the diameter of the crankshaft bearing journal.
note
If any journal has worn beyond the service limit, the crankshaft must be replaced. Due to the techniques used during manufacture, the crankshaft cannot be re-ground and no oversize bearings are available.

Main Bearing Selection

note
Minor differences in dimensions are compensated for by using selective bearings. For further information on bearing part number to colour cross-references, see the latest parts information.

Select the bearings as follows:

  1. Measure and record the diameter of each crankshaft main bearing journal.
  2. Measure and record each main bearing bore diameter in the crankcase (bearings removed, crankcase halves assembled and all fixings fully torqued).
  3. Select and install the correct bearings by matching the information found in the Main Bearing Selection Chart.
    4. Table

    For example:

    Crankcase Bore

    35.990 mm

    Crankshaft Journal Diameter

    32.978 mm

    Required Bearing

    Blue

    note
    It is normal for the bearings selected to differ from one journal to another.It is also normal for there to be two options of bearing shell colour. In such cases, pick the shell size that gives the greater running clearance.
  4. Install the new bearings.

Crankshaft End Float

Standard

0.15-0.30 mm

Service Limit

0.5 mm

note
Crankshaft end float is controlled by the tolerances in crankshaft and crankcase machining. No thrust washers are used. If the crankshaft end float is outside the specified limit, the crankshaft and/or the crankcases must be replaced.