Johnson Outboard Compression Chart

Its hard to find good data supporting what an appropriate measurement of cylinder compression should be in older outboard boat motors. I have owned several Johnson / Evinrude outboard motors, a couple of Mercury's, and at the time of this post one Yamaha four stroke. I have started this post as a repository of my findings regarding cylinder compression and hope to expand it over the years as my habit for tinkering with outboards continues.

• Yamaha Outboard Compression Chart
• Johnson Outboard Compression Chart
• 1990 Johnson 150 Outboard Compression
• Outboard Motor Compression Specs

Yamaha Outboard Compression Chart

1. Johnson Outboard Compression Chart Chromatic Tuner Imt 500 Manual If you are looking to replace your lower unit on your vintage Johnson/Evinrude outboard then eBay is a great place to find a good deal.
2. They dont adjust the heads or gaskets on the production line ( but I guess you have never been seen an outboard producton line) thats why many V4's had different comp on either bank especially on the higher compression engines like 115 and 140's. The heads are sand cast and different parts left to right.

April 19, 2015 at 2:44 pm #14276. The type and model is what matters in an outboard's compression readings. Not necessarily the hp or size. Some of the 9.5's had 65-75 lbs when new. The late 80's 200 hp looper motors only had about 85-95 lbs when new. Some outboard designs will read well into the mid hundreds.

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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. Its also rather hard to find where a manufacturer will say the compression range should be from this psi to that psi. What I have found unanimously is that the relative compression values between the cylinders should be within 10%. This source says modern two-stroke outboards should be in the 90 to 105 psi range. 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 sourceseems to confirm with my understanding that 60 psi in older outboards can sometimes be OK. Bottom line, if I was buying an older two-cycle outboard I would probably want to see compression values above 75 psi ESPECIALLY if I could not see it run.

Four cycle outboard motors produce much higher compression than two cycles. However, four cycle engine cylinder compression should still be within 10% cylinder-to-cylinder.

Older two cycle outboards, especially low horsepower, can run fine around 60 psi however above 90 psi is optimal. Free gfive mobile pc suite driver software. Four stroke/cycle engines produce much higher compression. The main thing to check is the difference between cylinder compression. Cylinder-to-cylinder compression readings that differ more than 10% reveal trouble.

Older two cycle outboards, especially low horsepower, can run fine around 60 psi however above 90 psi is optimal. Free gfive mobile pc suite driver software. Four stroke/cycle engines produce much higher compression. The main thing to check is the difference between cylinder compression. Cylinder-to-cylinder compression readings that differ more than 10% reveal trouble.

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Johnson Outboard Compression Chart

1990 Johnson 150 Outboard Compression

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Outboard Motor Compression Specs

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