• When a cylinder becomes oval, out of round or excessively worn it is time for a rebore.
  • This process involves removing the piston (s),having the cylinder (s) checked for size,ovality and for being parallel by using an internal micrometer.


This operation is critical to ensure the correct bedding in of the piston rings to maximize engine life and give ultimate performance.
During an engine rebuild the mechanic will typically measure the piston to bore clearance (the running clearance) and the ovality of the cylinder liner. However, if the motorcycle is running, there are a number of ways to check the cylinder condition without disassembling the engine.

The first indication that a motorcycle engine requires a rebore, and/or new rings, is when the rider or mechanic notices the engine emitting smoke. This applies primarily to 4-strokes. On 2-strokes the rider will notice a drop in performance and difficulty in starting.

Cylinder boring and sleeving for car engines, commercial engines and motorcyles from 4″ bore to 6.5-10″ bore.
Our workshop prides itself on its ability to handle most engine machining jobs, from the smallest to the largest, all done within a very fast turn around time.

We repair many different engines and cylinder heads including Toyota, Nissan, Mazda and all European brands.
We also cater for all types of motorcycle machining inc rebores with our sunnen hone, complete head rebuilding, crankshaft rebuilding, two and four stroke, broken bolt removal.

A cylinder is rebored because:
1. the piston to cylinder bore clearance is to large
2. the are deep scratches, grooves in the bore that hinder cylinder sealing
3. the bore is out round compared to the piston.

If the cylinder has an iron liner it can be rebored and a new piston is installed to match the bore. if the cylinder has some sort of “chrome” bore it must be rechromed or an iron liner installed with matching piston.

All these things are done to maximise cylinder sealing which equals power.
At a minimum new base gasket, head gasket, and top end bearing would be replaced.