Connecting Rod Big End Journal Checking, Measuring and Bearing Selection

Connecting Rod Big End Bearing Selection/Crankshaft Journal Wear Check

  1. Measure the bearing and crankshaft journal clearance as follows.
notice
The crankshaft journal clearances are measured using Plastigauge (Triumph part number 3880150-T0301).Do not turn the connecting rod and crankshaft during the clearance measurement as this will damage the Plastigauge.

  • Remove the big end cap from the journal to be checked.

  • Wipe the exposed areas of the crankshaft journal, and the bearing face inside the cap.

  • Apply a thin smear of grease to the journal and a small quantity of silicone release agent to the bearing.

  • Size a length of the Plastigauge to fit across the crankshaft journal. Fit the Plastigauge to the journal using the grease to hold the strip in place.

  • Lubricate the threads and under-head of the bolt with molybdenum disulphide grease. Refit the bearing and cap and tighten the big end bolts (see Connecting Rods - Installation).

  • Remove the big end cap from the journal being checked. Using the gauge provided with the Plastigauge kit, measure the width of the compressed Plastigauge.

Graphic from Connecting Rod Big End Bearing Selection_Crankshaft Journal Wear Check (gagd.svg)

Connecting Rod Big End Bearing/Crankshaft Journal Clearance

For specifications refer toCrankshaft.

notice
If the measured clearance exceeds the service limit, measure the crankshaft journal diameter.

Crankshaft Journal diameter

For specifications refer toCrankshaft.

note
If any crankshaft journal has worn beyond the service limit, replace the crankshaft. Because of the advanced techniques used during manufacture, the crankshaft cannot be re-ground and no oversize bearings are available.

Connecting Rod - 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.

  1. Select the correct big end bearing shell as follows:

  • Measure each crankshaft journal diameter.

  • Select the correct bearings by matching the information found with the chart below.

notice
All dimensions in millimetres.

Big end bearing selection chart

Shell Colour

White

Red

Connecting Rod Big End Bore Dia.

36.009

36.000

36.009

36.000

Crankshaft Journal Dia.

33.010

33.003

33.002

32.994

Running Clearance Range

0.064

0.036

0.061

0.032

Running Clearance Nominal

0.049

For instance:

Connecting Rod Big End Dia. 36.002

Crankshaft Journal Diameter 32.987

Required Bearing Red

note
Repeat the measurements for all connecting rods and their respective crankshaft journals.It is normal for the bearings selected to differ from one connecting rod to another.
  1. Install the new bearings in the connecting rod.
Graphic from Connecting Rod Bearing Selection (cdmx1.svg)

  1. Big end bearings

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