How much compression should a Mercury outboard have?

Results vary depending on whether the outboard is a Four-Stroke or a Two-Stroke. Good results for Four-Strokes should be 180-210 PSI, and Two-Strokes should be around 110-130 PSI. Here is everything that you need to know about outboard compression tests.

Is 120 psi good compression on outboard?

For a general number scale for compression. Two-stroke engines should be somewhere between 100-120 PSI per cylinder. Then four-strokes are going to be somewhere between 150-210 PSI! You will see a good compression reading of 150-160 PSI.

How do you fix low compression?

A healthy engine should have 100 PSI per cylinder. If two cylinders next to each other both have low pressure, a blown head gasket is a likely culprit. If you discover you do have low compression, the only solution is to replace the leaking part whether it’s the piston, piston ring, camshaft, head gasket or valves.

Is 150 psi compression good?

150 is realy good compression.

Will a 2 stroke Start with low compression?

Check Your Piston Rings Since the piston rings’ main job is to create compression in a two-stroke engine, they are usually the cause of a lack of compression. If your engine will start, but won’t hold compression or sputters and dies when you accelerate, there’s probably an issue with your piston rings.

How much does it cost to fix low compression?

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).

What is considered bad compression?

An engine compression test will tell you if your cylinders have good compression. As a rule, most engines should have 140 to 160 lbs. Of cranking compression with no more than 10% difference between any of the cylinders. Low compression in one cylinder usually indicates a bad exhaust valve.

What causes a 2 stroke to have no compression?

A common issue of a two-stroke engine is losing compression, and there are a few different reasons why this occurs. The most likely reason why a two-stroke engine has lost compression is an issue with the piston or piston rings. If there is a crack in the piston, air can escape and cause a lack of compression.

What should the cylinder compression be on a Mercury outboard?

From my research, cylinder compression values that people say are “acceptable” for low horsepower outboards seem to vary. They not only vary from the reporting individual but from manufacturer to manufacturer. For instance, a fully functional Mercury 25 Hp cylinder compression value may be significantly different than that of a Johnson 25 Hp.

What should the PSI be on an outboard compression test?

Results vary depending on whether the outboard is a Four-Stroke or a Two-Stroke. Good results for Four-Strokes should be 180-210 PSI, and Two-Strokes should be around 110-130 PSI. Here is everything that you need to know about outboard compression tests. How to do them and what the results mean for you! What Is A Compression Test?

What causes a bad compression test on a Mercury 2 stroke?

Even a small leak will result in a poorly performing powerhead as the fuel mixture will become lean causing the temperatures of the cylinder to increase. Lean air and fuel conditions increase cylinder temperatures beyond factory specifications.

What should the compression be on an Evinrude crank?

However if you watch the end my video below you will see that my 1979 Evinrude 6 Hp cranks easily cold ( 2 pulls) with 60 psi compression This source says the older two stroke outboards below 25 Hp should be between 75 and 85 psi. This source seems to confirm with my understanding that 60 psi in older outboards can sometimes be OK.