← Mazda Miata NA (1990-1997) problems

Short-nose crankshaft (1990 and early 1991)

Confirmed · Severity: High · Years: 1990-early 1991 (1.6L)

Symptoms

Crank pulley wobble; bolt failure; ultimately crankshaft replacement.

Cause

The early 1.6 timing-belt job included the crank seal, and improper reassembly of the pulley key can lead to the bolt failing. Hagerty says it affected about 1% of those cars; Mazda changed the crank nose partway through 1991.

Fix (summary)

Have a timing belt done by someone who knows the early engine; the crank seal is now usually skipped unless leaking. When buying, look for crank-pulley wobble.

Sources

• Your handy (1990-97) Mazda Miata buyer's guide — Hagerty Media (Mar 2021) (editorial; read 2026-10-15; full page read)

  “1.6-liter engines that came in the 1990 and early 1991 model years had a short-nose crankshaft”

• Used Miata Inspection List (2018 update) — Miata.net (editorial; read 2026-10-15; search excerpt only)
• Miata problems/maintenance by year — miatayear.com (editorial; read 2026-10-15; search excerpt only)
• NB to NA Miata Compatibility Guide — Redline Auto Parts (used-parts dealer; hands-on checks, own disclaimer) (vendor article; read 2026-10-15; full page read)

Summaries are in our own words. Not repair instructions; consult the factory service manual.