Measurement of the tolerance between piston and cylinder.
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In this video we will see:
00:00 Introduction
00:43 Ring wear
01:49 Measurement with calibrated gauge
03:04 Measurement with alexometer
04:20 Measurement by rocking the piston
This video presents the review that must be done when adjusting an engine, of the utmost importance to define if only rings can be changed, or if it has to be rectified, being able to be jacketed or take it to oversize.
The measurement of the cylinder or measurement of the sleeve is important because this is the tolerance between the piston and the cylinder, if it does not comply with said tolerance it will not give the expected durability, sometimes by not respecting this tolerance, at first the engine works well, but over time the ring will be working out of the groove and this will cause a rapid deterioration of the ring leading to the engine losing compression or passing oil to the combustion chamber and with this emitting blue smoke.
The manufacturer's tolerance tables are presented, which in this case is from the Chevrolet Chevy model, if it is decided to rectify, the tolerance of the tips of each of the rings will have to be verified, because if they are too closed outside the tolerance the The engine can be damaged when the rings expand, or oil will leak into the piston chamber.
A comparison of an old ring against a new ring is presented, where it is observed that the old ring, having wear on its tips, is greater than in the new ring, due to this, the ring also has an eyebrow or wear on its outermost part. because it was working out of the groove by dragging against the sleeve.
The first test to see the tolerance between the piston and the cylinder is done by inserting the piston with the skirt up and that the tips of it remain inside the cylinder approximately one centimeter, which is where the engine rings are working, and with a calibrated shim I proceed to measure the clearance between the piston and the cylinder, which in this case the manufacturer (Chevrolet Chevy) mentions in its electronic workshop manual that said tolerance is 0.01 to 0.03 mm (0.4 to 1.2 thousandths of an inch), introducing several shims and it can be Note that with this measurement I can observe 2.5 thousandths of an inch, which is a measurement that is outside the tolerance set by the manufacturer, and that this measurement is not the most accurate because the shim is a steel sheet and due to its width. It does not fit perfectly to the radius of the cylinder, but it does give us an approximation to the measurement that we are wanting to observe.
Later in the video I present the most precise measurement that is with the alexometer, in the video I measure the diameter of the piston skirt with a Vernier or caliper (the most accurate way to perform this measurement would be with a micrometer of the appropriate range ), with this measurement the alexometer is adjusted and we proceed to take the measurements in the engine wear axis which is perpendicular to the piston pin, observing measurements of 3.4 to 4 thousandths where with this measurement we can conclude that the piston clearance measurement or The tolerance between piston and cylinder is out of specification and the solution is to rectify, in this case it is preferable to jacket and change pistons because they already have wear and the engine remains standard, with this we will have several benefits, including which will be that the engine will have less fuel consumption and will have less heating than if it is sent to oversize, that this solution is also possible with changing pistons and opening the cylinder bore as it follows.
One last way to check piston and cylinder clearance is to place the piston in position and rock it perpendicular to the piston pin and see how much it moves, although this method is not accurate as we cannot quantitatively measure how much wear is.
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