Measuring jig

1. A measuring jig for measuring an inner diameter of a hole portion formed coaxially with a reference hole, the measuring jig comprising:

an insertion shaft inserted into the reference hole; and

a measuring instrument having a probe that is disposed around an axis of the insertion shaft and that is brought into contact with an inner wall of the hole portion,

wherein the inner diameter of the hole portion is measured by way of the probe by turning the measuring instrument about the axis, and

the measuring instrument is disposed on the axis.

2. The measuring jig according to claim 1 ,

wherein the measuring jig includes an operation shaft for turning the measuring instrument, and

the measuring instrument is positioned on an operation axis that is an axis of the operation shaft.

3. The measuring jig according to claim 2 , wherein the axis of the insertion shaft and the operation axis are disposed coaxially with each other.

4. The measuring jig according to claim 1 , further comprising a master gauge having: a positioning hole formed for positioning the insertion shaft; and an inner diameter reference hole provided coaxially with the positioning hole, an inner diameter of the inner diameter reference hole being preliminarily set to a reference value,

wherein the reference value that is an inner diameter of the inner diameter reference hole is measured by way of the probe by turning the measuring instrument about the axis of the insertion shaft in a state where the insertion shaft is positioned by the positioning hole with respect to the master gauge, and

a difference between the reference value and the inner diameter of the hole portion is measured.

5. The measuring jig according to claim 1 ,

wherein the hole portion is a valve hole portion of an engine including a cylinder head and a cylinder,

the cylinder head and the cylinder are integrally formed with each other, and

the measuring instrument is configured to turn in the cylinder.

6. The measuring jig according to claim 5 ,

wherein the valve hole portion includes a valve contact surface with which a valve face of a valve of the engine is brought into contact, and

the probe is configured to measure an inner diameter of the valve contact surface.

7. The measuring jig according to claim 1 ,

wherein the measuring instrument includes the probe, and a case that supports the probe in a swingable manner, and

the case is disposed on the axis.

8. The measuring jig according to claim 7 ,

wherein the case is formed into a box shape and the probe is supported on one end portion of the case in a longitudinal direction of the case,

the insertion shaft is mounted on the case, and

the axis of the insertion shaft is inclined with respect to a case axis that is an axis of the case in the longitudinal direction of the case.

9. The measuring jig according to claim 8 ,

wherein the case includes: an insertion shaft mounting surface on which the insertion shaft is mounted; and an operation shaft mounting surface positioned on a side opposite to the insertion shaft mounting surface, and

the operation shaft for turning the measuring instrument is mounted on the operation shaft mounting surface.

10. The measuring jig according to claim 1 , wherein the insertion shaft includes a stepped portion that is brought into contact with a bottom portion of the hole portion.

11. The measuring jig according to claim 1 , wherein the insertion shaft is supported in a state where a length of the insertion shaft in an axial direction is adjustable with respect to the measuring instrument.

12. The measuring jig according to claim 4 ,

wherein the insertion shaft includes a stepped portion that is brought into contact with a bottom portion of the hole portion, and

the master gauge includes a spacer that is interposed between the stepped portion of the insertion shaft and the master gauge.

13. The measuring jig according to claim 12 , wherein the insertion shaft is supported in a state where a length of the insertion shaft in the axial direction is adjustable with respect to the measuring instrument.

14. The measuring jig according to claim 5 , wherein the measuring jig includes an operation shaft for turning the measuring instrument, the operation shaft passing through the reference hole and extending to the outside of the cylinder head.