You should start to worry if one of your cylinders is getting close to 100 psi. Most new engines in good condition compress at around 175 psi. Suppose that #4 cylinder were at 120 psi, the difference ratio would be 31.4% which would indicate excessive wear in the cylinder.

Engines will need at least 100psi to run, and they might not run well at this low on compression. Most healthy motorcycle engines will have 120+psi. I would investigate further with any readings under 110psi. Readings on all cylinders should be within 10% of each other.

An engine with low compression in one cylinder will present itself by having a misfire and running rough while no compression in all cylinders will cause the engine not to start. There are many different low compression symptoms which will cause the engine to run abnormally.

A compression test reveals the condition of your engine’s valves, its valve seats, and piston rings and whether these parts are wearing evenly. Healthy engines should have compression over 100 psi per cylinder, with no more than 10 percent variation between the highest and lowest readings.

around 90psi

If you experience compression loss in one cylinder of the engine, it can cause misfiring and poor vehicle performance. A decrease in power output is a sign of worn-out internal parts. Sometimes, an engine misfire code may indicate compression loss, but first, check the ignition and fuel for problems.

Fixing low engine compression issues involves repairing or replacing the part(s) causing the problem. If you decide to have a professional mechanic do the compression test, it’ll cost you anywhere between $100 and $200. You’ll also need to factor in the cost of repairing or replacing the damaged part(s).

The term “compression” refers to the pressure that builds up inside the piston chamber, as a combination of fuel and air is squeezed, and a spark is applied. A loss of compression may result when the pistons are worn, the seals around your pistons are worn, or a push rod has become bent or broken.

When drivers notice excessive oil consumption, white or gray exhaust smoke, poor acceleration, and/or overall loss of power or poor engine performance, they may be seeing signs of worn piston rings.

Rod knock typically sounds like a low-pitched knocking sound that can be heard deep in the engine. As the engine speeds up, the frequency of the noise will increase, but you can hear it at any engine speed.

Bad Lifter Symptoms

• #1 – Sticky Lifters. A sticky lifter remains in a collapsed state instead of going up and down.
• #2 – More RPM Causes More Noise.
• #3 – Misfires.
• #4 – Dead Cylinder.
• #5 – Check Engine Light.