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1.6L 16v - Z16LER Z16LET
Manufacturers
1.6L 16v - Z16LER Z16LET
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ARP main bolt kit as a replacement for the original bolts on Opel and Vauxhall 1.6 Turbo petrol engines.
In the mid-2000s Opel turbocharged its 1.6 litre petrol four-cylinder family to power its sportiest models. The Z16LET, a 1.6 litre DOHC 16-valve four, powers the Astra and Corsa in their OPC versions, sold as VXR on the British market.
The Z16LER shares the same architecture, while the following generation, designated A16LER and A16LET, carries the block over with further development. These factory-turbocharged engines are a popular tuning base: the block accepts power levels well above stock once the bottom end is reinforced.
Main bolts hold the main caps to the engine block, and therefore clamp the crankshaft in its bearings. They constantly absorb the loads transmitted by the rotating assembly: on every combustion event, the load applied to the crankshaft tries to lift the cap out of its register. As soon as boost pressure rises, the preload of the original bolts becomes insufficient: the cap moves, fretting appears at the block-to-cap interface and crankshaft flex increases.
Forged from 8740 chrome moly steel, ARP main bolts feature a reduced wrenching head, a large underhead radius that spreads stress, and threads rolled after heat treatment. This aerospace-derived process gives far greater fatigue strength than a bolt threaded before heat treatment. Every kit is supplied with hardened parallel-ground washers, which ensure a flat seat and a consistent torque figure.
| Brand | Grade / material | Fastener type | Thread | Length | Number of pieces |
|---|---|---|---|---|---|
| ARP | 8740 chrome moly | Main bolts | M10 x 1.50 | 60 mm | Not specified |
| Part number | Torque value | Lubrication |
|---|---|---|
| 117-4711 | 73.2 Nm (54 ft-lbs) | ARP Ultra-Torque recommended |
Unlike rod bolts, which are checked by stretch measurement, main bolts are installed to torque: adherence to the specified value determines preload and therefore crankshaft running clearance.
Founded in California in the early 1970s by Gary Holzapfel, a former aerospace industry engineer, ARP (Automotive Racing Products) grew from a simple observation: in motorsport, engine failures often came from undersized fasteners. Fifty years later, the company designs and manufactures thousands of part numbers in the United States (head bolts, studs, rod bolts, main hardware) and equips most professional grids, from drag racing to endurance.
A main bolt part number is specific to an engine family: it depends on thread, usable length and cap geometry. Then comes the choice between bolts and studs.
| 8740 chrome moly is ARP's reference steel for bottom-end hardware: a chrome-molybdenum steel, quenched and tempered, with threads rolled after heat treatment. Bolts replace the originals directly and install without modification, while main studs, permanently fitted in the block, offer even more precise alignment but sometimes require machining of the block. For a Z16LET-based build, the bolt kit offers the best gain-to-simplicity ratio. |
Bolts are installed on a bare block, with journals and bearings clean and dry, and caps in their original order and orientation. Tightening is done to torque, in several progressive cross-pattern passes, with the recommended assembly lubricant: lubricant choice directly affects the preload achieved at a given torque. Checking main bearing radial clearance with plastigauge after tightening is strongly advised, before reassembling the rotating assembly.
| Make | Engine code | Displacement | Range concerned |
|---|---|---|---|
| Opel / Vauxhall | Z16LET | 1.6 Turbo 16v | Astra, Corsa OPC / VXR |
| Opel / Vauxhall | Z16LER | 1.6 Turbo 16v | Astra, Corsa OPC / VXR |
| Opel / Vauxhall | Z16LEH | 1.6 Turbo 16v | 1.6 Turbo range |
| Opel / Vauxhall | A16LER | 1.6 Turbo 16v | 1.6 Turbo range |
| Opel / Vauxhall | A16LET | 1.6 Turbo 16v | 1.6 Turbo range |
Dimensions: M10 x 1.50, 60 mm length
A main bolt kit costs a fraction of a bottom-end rebuild. If a main cap moves because of insufficient preload, consequences range from fretting of the mating surfaces to destruction of the crankshaft and block. Fitting ARP bolts while the engine is open (with the block already accessible) removes that risk for a marginal investment.
