Compression Question????

[fdheld34]

I have a 1997 Johnson Oceanrunner
Compression as follows
looking at rear of block
left side
120
120
85

right side
120
120
90

Per mechanic possible rebuild of engine or sell as blown motor???
Motor runs fine...just never had compression test done before
Any other suggestions decarb etc. etc.
I am aware that there is no mechanic in a can but just trying to come up with ideas etc?
Thanks in advance
-Fred H

[77SceptreOB]

You can try a De-carb process, but those #'s are pretty far off. General rule is: the range should NOT be more that 10 psi or max max of 10% differnce. That would be a 12psi max. You are 35 psi, surprised the engine runs well w/ those #'s.

Did you check the compression when the engine was warmed up?? Also was fuel/oil running through it at the time of the test?(Kill switch in safe mode) All the plugs out at when you cranked it over?? All of the above can affect the #'s as I have read in many articles on the subject.

I just went through this exercise myself in the past month. Fortunately my max range was 9 psi.

[fdheld34]

oops...not 120 but 110..typed it wrong
so let me redo!!
left
110
110
85
right
110
110
90
still looks like off more than 10 percent
Any more suggestions..rebuild....etc???
thanks again
-FRED

[Old'sCool]

You need to know what the specification is. Some of those motors had two opposing cylinders lower

[Bigshrimpin]

Those bottom two are toast. Pull the heads and take a look at the damage. Scoring is probably minimal at 80psi . . . but do not run that motor anymore . . . don't even turn it over (unless you do it by hand slowly with lots of oil). I bet you have two stuck rings and some nice aluminum paint inside the bottom two with light scoring. If you stop now you can probably get away fixing the motor with a hone and two new pistons. Don't even bother decarbing at this point. Pull the heads and look. If you just have stuck rings and no cylinder wall damage . . . then consider yourself extremely lucky. The nice thing about that motor is that you can pull both pistons out without cracking the block open.

[fdheld34]

Did you check the compression when the engine was warmed up?? Also was fuel/oil running through it at the time of the test?(Kill switch in safe mode) All the plugs out at when you cranked it over??

Motor was cold when compression done
all spark plugs removed and remote starter used at motor


Tim... wish you were closer.....

I will check specs just in case..I really dont feel like dumping money in that I dont have!!!!

[Bigshrimpin]

Fred - 1st thing I would do is buy a compression tester yourself and double check the mechanics claims on the bottom two. If they test low . . . pull the heads.

if the scoring isn't bad, you can do a 2 hole fix on that motor w/o a total rebuild. It'll take about 1 day and you'll need 2 new head gaskets, 2 new pistons and rings, bearings (may be able to reuse), intake gasket, a ball hone that will fit that motor, lots of oil, wd-40, locktite, gel seal, and carb rebuild kits. It's a bit of a hack fix, but it'll work if you keep everything clean clean clean. The alternative is to sell it. Parts will probably run $300 - $400, so you have to make the call and decide if you feel mechanically inclined.

[thehermit]

You should pop a head....and have a look. Tim walked me thru this exact repair. Yes you can pull the reed block unbolt the rod and push the piston out. After doing that you can "de glaze" with a hone. I did this to one cyl that had a stuck ring (my fault) on my 225. Compression went from 80 back up to 120 where the rest were. Parts for the piston, rings, rod bearings etc was just over 200ish I think. Its a pretty basic motor. I dont think I would move it into the "parts motor" catagory without looking inside 1st.

[76Red18]

Mine's 105 - 108 and 98 on the bottom port. When I rebuilt a couple years ago, they were 110 except that bottom one at 105.

[Bigshrimpin]

John - Do you have that picture of the piston with the stuck ring, so fred can see what 80psi looks like in that motor?