During overhaul inspection of a horizontally opposed engine's crankcase, a technician measures the stretch of each through-bolt using a specialized dial-bore gauge to check for permanent elongation. One through-bolt shows stretch exceeding the manufacturer's maximum allowable limit. What is the significance of this finding?
- AThe stretch is normal and expected after the first engine run and requires no action
- BThe stretch indicates the bolt has been overtorqued or fatigued and must be replaced, not reused
- CThe bolt has simply been torqued to the low end of the acceptable range and is serviceable
- DThe bolt can be reused after being re-torqued to the original specification
Show answer & explanationAnswer & explanation
Correct answer: B. The stretch indicates the bolt has been overtorqued or fatigued and must be replaced, not reused
Through-bolts are torqued into their elastic range to clamp the crankcase halves together, but permanent stretch beyond the specified limit indicates the bolt has been overstressed into plastic deformation or fatigued from repeated loading cycles. Such a bolt has lost its clamping integrity and must be discarded and replaced with a new one; it cannot be restored by re-torquing.
Why the other options are wrong
- A. Some minor stretch is normal, but exceeding the manufacturer's specified maximum is not acceptable.
- C. Stretch beyond the limit is not related to torque range selection, it indicates permanent deformation.
- D. Re-torquing cannot restore a bolt that has already permanently stretched beyond its elastic limit.
Crankcase Through-Bolt Stretch Check
A precision measurement of through-bolt length or diameter change used to detect permanent elongation from overtorque or fatigue during crankcase overhaul.
- Through-bolts clamp crankcase halves together under high tension
- Stretch beyond manufacturer limits indicates permanent deformation
- Bolts exceeding the stretch limit must be replaced, never reused
Memory trick: A stretched bolt is like an overused rubber band — once it's past its limit, it's junk.