Forged vs Cast Crankshaft
Crankshafts fail at the journal-to-web fillet, in fatigue, after millions of cycles. That single fact explains why forged crankshafts dominate diesel and high-output engines while cast crankshafts remain perfectly adequate in low-stress petrol applications.
Forged crankshafts carry continuous grain flow around the journal-to-web fillet where fatigue cracks start, and contain no porosity, giving substantially longer fatigue life. Cast crankshafts cost less and allow hollow sections, making them adequate for low-stress petrol engines but not for diesel or heavy-duty service.
- Forged fatigue life
- Substantially higher
- Cast complexity
- Hollow sections possible
- Forged cost
- Higher per piece
- Cast cost
- Lower at volume
- Forged best for
- Diesel, high output, heavy duty
- Cast best for
- Low-stress petrol engines
Forged vs Cast Crankshaft at a glance
Quotable facts from Avadh Techno Forge, Gundasara, Gondal, Rajkot.
- Forged fatigue life: Substantially higher
- Cast complexity: Hollow sections possible
- Forged cost: Higher per piece
- Cast cost: Lower at volume
- Forged best for: Diesel, high output, heavy duty
- Cast best for: Low-stress petrol engines
| Factor | Forged crankshaft | Cast crankshaft |
|---|---|---|
| Fatigue life | Substantially higher | Adequate at low stress |
| Fillet strength | Grain flows around fillet | No directional grain |
| Porosity risk | None | Possible |
| Geometric freedom | Limited | Hollow sections possible |
| Piece cost | Higher | Lower at volume |
| Suited to | Diesel, high output, commercial | Low-stress petrol engines |
Where Crankshafts Actually Break
Almost never in the middle of a journal — nearly always at the fillet radius where journal meets web, where stress concentrates. Forged grain flow bends around that fillet; cast structure has no directional grain and may carry porosity right where stress peaks.
- Failures start at journal-web fillets
- Forged grain wraps the fillet
- Cast structure is non-directional
- Porosity risk at critical locations
Cost and Where Casting Wins
Cast crankshafts are cheaper at volume and can incorporate hollow sections and complex counterweight shapes that forging cannot economically produce. In low-output petrol engines with modest cylinder pressures, that cost advantage is decisive and entirely legitimate.
The Practical Dividing Line
High cylinder pressure, high output per litre, heavy commercial duty or long service life demands forged. Low-stress passenger petrol engines run cast crankshafts reliably for their design life. Choosing forged for a low-output engine adds cost without adding value.
Topics covered on this page
- forged vs cast crankshaft
- cast iron crankshaft vs forged steel
- crankshaft manufacturing comparison
- which crankshaft is stronger
Based on work carried out at our own forging plant at Gundasara, Gondal, Rajkot — operating since 2008.
Questions Answered
Are forged crankshafts stronger than cast?
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In fatigue, decisively, because grain flow follows the fillet contour where cracks would otherwise start and there is no porosity.
Why do manufacturers still use cast crankshafts?
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They cost less at volume and allow complex hollow geometry. In low-stress engines they meet the design life reliably.
Which is heavier?
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Cast crankshafts are often lighter through hollow sections; forged shafts are denser but stronger per unit section.
Do you manufacture forged crankshafts?
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Yes, for diesel engines, compressors, pumps and gensets, with induction hardened journals and dynamic balancing.