Connecting Rod for Diesel Engines: Weichai, Baudouin and Yuchai

A connecting rod transfers the firing impulse from the piston to the crankshaft, and its big end carries the highest alternating load of any bearing in a diesel engine. Because the rod is a matched assembly rather than a single part, buying the right one depends on the rod number, the piston pin diameter and the weight class of the set.

Connecting rod part numbers by engine

The table below lists the rod assemblies we hold for the Weichai, Baudouin and Yuchai families. Use the engine plate and the old rod number together — two rods can share a length and big end diameter and still differ in weight class.

What decides fitment

Three dimensions decide whether a rod will work, and all three are measurable:

• Big end bore — must match the bearing shell and the journal after any regrind.
• Small end bush diameter — must match the piston pin; a worn bush loads the pin unevenly.
• Centre-to-centre length — changes compression height if wrong, which shows up as piston-to-head contact.

Weight class is the fourth factor and the one most often missed. A rod that is 20 grams heavier than the rest of the set produces vibration that is usually misdiagnosed as a crankshaft or damper fault.

Rod bolts are not reusable

Rods on these engines use torque-to-yield bolts. Once tightened they have passed their elastic limit, and reusing them loses clamping load exactly when the cap is under load. A stretched bolt lets the cap fret, the bearing spins and the journal is damaged within a few thousand kilometres.

Order new bolts with the rod, and check the cap mating surface for fretting before assembly. A cap that has already fretted will not hold torque even with new bolts.

Inspection points before fitting

1. Check the rod for bend and twist on a proper fixture, not by eye.
2. Measure the big end bore with the cap torqued to specification.
3. Inspect the small end bush for scoring and measure clearance to the pin.
4. Confirm the weight matches the rest of the set.
5. Check the oil squirt hole, where fitted, is clear.

Frequently asked questions

Can a connecting rod be straightened?

No. A bent rod is replaced; straightening a forged rod changes its fatigue life and it will fail again.

Are rod bearings included?

No. Big end shells are ordered separately and must match the journal size after any regrind.

Do I need to replace all six rods?

Only if weight matching or damage requires it. When replacing fewer than a set, have the new rod weight matched to the others.

What causes rod bearing failure?

Usually oil starvation, incorrect clearance or a stretched bolt that lost clamping load.

Ordering

Send the old rod number, a photograph of the big end with a ruler alongside, and the engine plate. Those three items identify the variant faster than any catalogue, and they avoid a return on a part that fits but does not match the set.