Maruha 85mm Crankshaft for Mazda MX-5 NA NB 1.8

£1,020.64 inc. VAT

Available to order — usually ships in under 3 weeks

Maruha offers 3 types of custom crankshafts for the Mazda MX-5 NA and NB 1.8. The standard size 85mm crank, the spicy 87mm crank and the Carolina reaper of crankshafts, their 89mm stroker kit.

This is the OEM size 85mm crankshaft. Maruha developed this in response to Mazda discontinuing the OEM genuine crankshaft but features several design improvements over the standard crank. One of the biggest is the extended pulley boss at the front of the crank. The oil pump, timing belt and front pulley are all attached right on the very edge of the crankshaft and over time, this edge can become fatigued resulting in uneven wear of both the pulley and the crankshaft. Once worn, this will unbalance the front of the crankshaft putting major strain on some of the most critical components of the engine. Maruha have solved this by extending the crank out 14mm from the OEM pulley, setting all the load of the belts and oil pump away from the edge and providing a solid surface for this load to be transferred from.

Maruha’s 85mm crank is also around 1kg lighter than factory. With the 1.6 engine often being favoured for its free-revving qualities, this shedding of weight will lead to the 1.8 engine feeling as revy as ever while maintaining the added torque the extra displacement brings.

When building a fresh engine, one of the major considerations should be how long you’ll want the engine to last. Even complete rebuilds normally use a second-hand crank, but there may be issues even the most experienced mechanic cannot find. This is the main issue Maruha sought to address with this 85mm replacement crank; if you’re completely refreshing a stock engine or building one to take power, you’ll want to build it to last as long as possible as crank issues will require the entire engine to be disassembled. A new crank provides much-needed assurance that an engine can easily last hundreds of thousands of miles more.


  • Cast and machined from 43040 Chromoly Steel
  • Several design improvements over the OEM crankshaft
  • Compatible with OEM rods, pistons, main & rod bearings
  • Retains standard displacement

Additional information

Shipping Weight 14 kg
Shipping Dimensions 50 × 16 × 16 cm



Mk1 (89-98), Mk2 (98-05)

Warranty information

Warranties cover defects in materials and workmanship only. Warranty is for replacement of a similar product, repair of the original product or refund of the purchase value only and excludes all labour and incurred charges including towing, fitting, inconvenience, and purchases of other manufacturer's products. The warranty is good for the period stated in the additional info tab from the date of purchase. Mileage warranties are for road use only and proof of mileage is required. Products must be installed by an independent experienced professional mechanic and the suspected defect must be present at the outset. The warranty does not cover damage caused by incorrect installation, failure to comply with the maintenance requirements of the vehicle, processing or otherwise changing the product, ordinary wear and tear, or any other external influences. Warranties are invalid if the product is used for racing, rallying, drifting, track days or any other form of motorsport or competition. Please refer to the manufacturer's own warranty documentation for more information.

Making a warranty claim

Proof of purchase receipt showing the date of purchase, proof of mileage at installation, proof of current mileage and invoice of the work undertaken by an independent experienced professional mechanic must be supplied along with the returned products for a warranty claim to be considered. If your vehicle needs to be used whilst your warranty claim is considered replacement parts from the same manufacturer should be purchased through BOFI Racing. In the event of a successful warranty claim, we will refund the card that was originally used to purchase the replacement parts, in full or in part depending on the nature of the claim. BOFI Racing reserves the right to make full or partial compensation at its sole discretion depending on the condition and mileage use of the returned suspect parts. For example, if you have used the part for several thousand miles before a defect is noticed, only partial compensation may be offered.

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