BSA M21
Real ownership data from 245 UK M21 motorcycles — mileage, MOT pass rates and the faults that actually come up, taken from DVSA test records rather than opinion.
Most common M21 problems
Ranked by how often each fault appears in this model's MOT history.
| Fault | Severity | Share of faults |
|---|---|---|
| Lights and indicators | fail | 10.6% |
| Other | fail | 7.5% |
| Brakes | fail | 4.9% |
| Suspension | fail | 3.9% |
| Steering and head bearings | fail | 3% |
| Fluid leaks | fail | 2.8% |
| Tyres | fail | 2.6% |
| Electrical | fail | 2.4% |
Advisories (wear noted but not failed) are excluded above; the most common is wheels.
M21 mileage and reliability by year
Use this to judge whether a specific bike is high or low mileage for its age.
| Year | Examples | Median mileage | Miles/year | First-time pass |
|---|---|---|---|---|
| 1998 | 5 | 12,700 mi | 512 | 89.66% |
| 1990 | 7 | 34,883 mi | 380 | 97.37% |
| 1985 | 5 | 26,817 mi | 162 | 88.24% |
| 1984 | 8 | 21,864 mi | 229 | 100% |
| 1961 | 19 | 25,751 mi | 193 | 93.88% |
| 1960 | 14 | 18,496 mi | 78 | 94.64% |
| 1959 | 15 | 7,780 mi | 118 | 91.67% |
| 1958 | 9 | 13,867 mi | 139 | 91.67% |
| 1957 | 11 | 17,237 mi | 130 | 100% |
| 1956 | 10 | 10,787 mi | 308 | 81.25% |
| 1955 | 22 | 36,194 mi | 316 | 92.31% |
| 1954 | 16 | 17,334 mi | 334 | 87.88% |
| 1953 | 14 | 14,354 mi | 224 | 95.56% |
| 1952 | 8 | 13,803 mi | 200 | 91.43% |
| 1950 | 11 | 18,568 mi | 42 | 94.44% |
| 1948 | 6 | 23,608 mi | 34 | 89.47% |
| 1947 | 8 | 29,357 mi | 698 | 88.46% |
M21 questions, answered with data
What are the most common problems with the BSA M21?
Across 245 UK examples, the most frequently recorded MOT faults are lights and indicators (10.6% of all recorded faults), other (7.5% of all recorded faults), brakes (4.9% of all recorded faults).
What is average mileage for a BSA M21?
The median BSA M21 in the UK has covered 19,579 miles, and typically rides about 180 miles a year. Half of all examples fall between 4,482 and 43,976 miles.
Is the BSA M21 reliable?
92.72% of BSA M21 MOT tests are passed first time, with an average of 0.46 faults recorded per test. This is measured from DVSA MOT records, not owner opinion.
Based on DVSA MOT test records for 245 BSA M21 motorcycles registered in Great Britain and Northern Ireland. Contains public sector information licensed under the Open Government Licence v3.0.