1988 Johnson 90hp compression

[jdupree]

My 170 that I just bought has a 1988 90hp Johnson.  When I did the compression check it averaged between 90 and 95 psi on all 4 cylinders.  Is this good Motor runs great but have not run it under load yet.  Just curious if that is good compression or not Thanks for any input,

[Mr. Osprey]

It's all right. As long as the numbers are relatively good and within 5 psi of each other.

[jdupree]

Mr. Osprey,

Thanks for the info.  When you say that "its allright" do you think that is lower than normal compression   I have always heard as you said that as long as all the cylinders are close that you are fine.  I was just thinking if I was close to a re-build or if 90 to 95 is ok

[jy118lfd]

Just try running it under load. When you get it in the water shoot for 5800 to 6000 with a light load. 90 to 95 sounds good. Compression gauges vary just so long they are within 15lbs of each other. Most outboards do not wear out they are destroied by lack of matience. Keep the fuel fresh and mixed at 50 to 1 with a tcw3 oil. If still using the vro make sure no water is in the oil tank as this has caused many a blown powerhead.

Most important is getting it setup to run the  proper rpm as wot even if you don't run it wide open.

Outboardrepairs.com is a great site to post questions like these as there are some real experts on that site as well

[JimCt]

Agree.  Compression's fine for the age & likely number of hours on it.  If you had, say, 90-90-90-50, then red flags would be out.  As said above, use a top-quality TCW3 oil and stay up on the maintenance.  Avoid mixing different brands/types of oil, even if all TCW3's. Some blends are not compatable with others.

Other item to check is the lower unit.  Change out the L/U lube before you use the motor.  Take the boat out for a jaunt for an hour or so, haul it and dump out the lube into a container and inspect it for milkiness or chunks of metal.  If the lube looks clean & clear your seals should be OK.

How'd the spark plugs look when you pulled them?  If they looked fouled, change them.  Check the motor mfg's plug recommendation.  Many times you'll find the wrong plugs in a used engine; last two used motors I bought had the wrong plugs.