Big End Shells Undersize 020 for JAP 4/3 Engines are genuine JAP bearing shells used on the connecting rod big end to restore correct oil clearance on reworked crankpins. Supplied as vintage unused old stock, they are made from durable, steel-backed bearing material for consistent load carrying and longevity. The 020 designation equals 0.020 inch undersize (about 0.508 mm), suited to crankshafts ground to this dimension. Marked with OEM part number 18474/020, they offer an assured match to original specification on JAP 3 and JAP 4 petrol engines typically found in compact plant, stationary equipment, and vintage garden machinery. Fitting the correct undersize shells reduces knock, improves oil pressure at the rod journal, and helps the engine run smoothly and reliably.

Key Features:
– Genuine JAP part for correct fit and compatibility on JAP 3 and JAP 4 engines- Undersize 0.020 in (approx. 0.508 mm) to suit a 20‐thou re-ground crankpin- Steel-backed bearing material for strength and stable running clearances- Helps restore oil film integrity, reducing big-end knock and wear- Precision-made to OEM No. 18474/020 for reliable alignment and seating- Suitable for engine rebuilds and restorations of classic JAP petrol units- Vintage unused old stock; may show tarnish or storage marks without affecting function- Supports smooth rotation of the connecting rod under load at operating temperature- Straightforward to install for competent mechanics when used with correct torque and clearance checks- Enhances longevity when paired with clean oil and proper running-in procedure

Typical Applications:
Used during engine overhauls after crankshaft regrind to 0.020 in undersize, to replace worn big-end bearings on JAP 3 and JAP 4 engines. Common in the refurbishment of vintage plant, pumps, generators, rollers, and garden machinery using JAP petrol power units, where restoring oil pressure and eliminating rod knock is required.

Also known as:
Big-end bearings, connecting rod shells, con-rod bearings, rod inserts, 0.020 in undersize shells (approx. 0.51 mm), 20‐thou undersize bearings, crankpin shells, big-end bushings.

Fits Models:
JAP 3, JAP 4, JAP3, JAP4

Product Specifications