Engine Repair Work Example 1

WorkKey Level: 4
NATEF Automotive Tasks: I.A.8, VIII.A.8

When doing a cylinder balance test, you come up with the following results.

Cylinder	RPM drops from 650 to
1	575
2	560
3	630
4	570

Predict which cylinder is not producing power.

The manufacturer requires at least a 10% drop in RPM when a cylinder is killed. Complete the following chart.

Cylinder	Percentage of Drop
1
2
3
4

According to your calculations in the above chart, which cylinder is not producing power?

Solution

Student predictions: Answers may vary.

Cylinder	Percentage of Drop (rounded to nearest tenth of a %)
1	(650 – 575)/650 = 75/650 = 11.5%
2	(650 – 560)/650 = 90/650 = 13.8%
3	(650 – 630)/650 = 20/650 = 3.1%
4	(650 – 570)/650 = 80/650 = 12.3%

10% drop of original amount = (0.10)(650) = 65 rpm
Acceptable amount must be (650 – 65) = 585 rpm or less.

Cylinder 3 is not producing power. 
3.1% < 10%
630 rpm > 585 rpm