Cylinder Block Measurements

Theory Background:
I am going to measure the components of the Cylinder Block to make sure every thing is in order and there is no damage to parts such as the pistons and the crankshaft.
Piston - The piston is a metal object the sits in the piston chamber. It moves up to compress the air/fuel mixture on stroke 2 and push out the exhaust gas on stroke 4, and it moves down to let the air/fuel mixture in on stroke 1 and let the mixture ignite on stroke 3.
Crankshaft - The crankshaft rotates around to move the pistons up and down in time to complete the 4-stroke cycle.


Visual Inspection of Pistons:
Before you do any measurements on the cylinder head it is important to do a visual inspections of the components e.g pistons. To do this simply check the surface for scuffing or damaged.

Piston Diameter:
To measure the piston diameter, what you do is get a micrometer and measure the diameter form the skirt of the piston.

Cylinder Bore:
For measurements of the cylinder bore you need to measure both the Y and X axis on 3 different positions (top, middle and bottom). We do this to check the ovality of the cylinder bore. For example:

This is where and how to measure each point of the cylinder.

Piston Clearance:
To find the piston clearance, you get the measurements the largest cylinder bore diameter and of each piston diameter. Then, you subtract the piston diameter from the cylinder bore cylinder. For example; cylinder bore diameter 1 = 77.99mm and piston 1 diameter = 77.88mm, so the piston clearance = 00.11mm (77.99mm - 77.88mm = 00.11mm).

Piston Ring Clearance:
To check the piston ring clearance, all you do is find the specifications for piston ring clearance for that engine, then get a feeler gauge and put it in between the piston ring and the piston ring gap. If it stays under the maximum specification then it's good, if not then the piston ring needs to be changed.

Piston Ring End Gap:
For this measurement, what you need to do is put a piston ring into the cylinder and then check the gap between the ends of the piston ring whilst in the cylinder.

Crankshaft Main Journals:
To measure this, you get a micrometer and measure the diameter of each main journal on 2 points and on an A and B axis. This measures both the taper and ovality of the main journals.

Crankshaft Big End Journals:
For this measurement, you do the same as the previous measurements. But you measure the big end journals as opposed to the main journals.