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Johnson 90 HP 1985 J90TLCOS Electrical Doozy

Racer is concerned that you won't check the covers. This will give a view of the cylinders and pistons. He is suggesting you do that because of low compression, however we all know that your gauge could be low too.....and since all cylinders are equal, that could be the case. I suggest that you first try to test with another gauge and/or try your old gauge again but crank motor with a fully charged battery (12.65 volts or better) and.....crank until you see max compression on each cylinder.
 
Then, if still only 90 psi in each cyl. we suggest to remove at least one aforementioned cover.....perhaps the top one that's easiest to access. Next post a picture of the rings and piston looking through the opening. Size photo to under 1000k, otherwise the Forum will not be able to process it. Click "go advanced", then up on toolbar click on the paperclip.....then follow the prompts. As you might suspect, more interest is often generated with photos included in the post. Racer is a phenomenal tech, perhaps he will return to help.
 
I certainly do plan on looking into the covers. I will absolutely post back. Im one of these guys that likes to keep the thread updated. Thanks for the tips on uploading ill see what I can get done during lunch. Yes I understand silly questions can wear an experienced tech out but i do appreciate all the help. I was simply confused on the locations of the covers. I looked up the part on ebay and now understand where to pull them off. I will also recheck the compression after inspecting through the covers. I am trying to keep the starter jumping at a minimum so I dont burn the starter up, how do I know if i get to max compression? Thanks again
 
I suggest rechecking compression before cover removal. You could easily see 120 psi. Then you can move to other concerns and problems. Make sure the gauge stops climbing....then you know you are at max. Auto part stores loan out gauges too. Starter should be okay, just wait a couple minutes between cylinder.....and.....as aforementioned, have all plugs out to relieve load on the starter. The starter is engineered to crank 4 cylinders at 130 psi each.....so cranking up only one cylinder at a time is child's play, for a healthy starter.
 
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Hold up here before you take parts off of the motor, what do you mean you stopped the flywheel at 90 psi. For a compression test you keep that flywheel turning until the needle in the gauge stops. Re do the compression test correctly!
 
I was where you are some 50 years ago and had no mentors......still poked my way through without destroying anything. This.....and other forums.....can educate rapidly and accurately. Maintain your humility and you will succeed. There is experience abound here. Set aside any unintended insults....everyone is here to share knowledge....I'm learning lots all the time too.
Thanks Mr. Scott. Bassboatin,....yes a little wd40, mixed gas sprayed in....whatever....will lube during the testing.
 
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Thanks. Im in my 20s and have discovered a love for mechanics in the past years due to a constantly malfunctioning f150. I cannot express how grateful i am for the help. Going to try a lottle pb blaster in and report back
 
Okay readings are as follows: top right cylinder 115. Bottom right 90. Top left 95. Bottom left 90. I guess next step is to pull covers right?
 
There are no " valve covers " near the sparkplugs.----Just pull the cylinder heads off 10 bolts each.------Your compression test results are not encouraging to say the least !
 
Pistons.jpgCover.jpgpiston scoring 1.jpg

Hey guys, more pics coming its just sort of a rigamarole to get them uploaded. I popped the heads off and found significant rust under the valve covers and a lot of carbon build-up but nothing glaringly obvious that is wrong. There is some really light crosshatching in the valves but aside from that I am not sure where the problem lies. maybe some of you guys with a keener eye can help me out here.
 
Mistaken terminology- how about cylinders? Is that correct? Do these pics tell any story? Looks like a ton of carbon buildup. Im processing more pics now. Thanks for the help guys.
 
Carbon is fine. The rust is a concern put the heads back on with the old gaskets and fill the cylinders with tranny fluid and let sit for a couple days.
 
So no use in trying to clean the heads with marvel mystery or some such? I will put some aft in there and do as you suggested. How much atf you figure per cylinder? When I had the heads on and turned the flywheel by hand there was a spot when turning the flywheel you could feel some resistance. Should I take anything else apart while ive got the heads off? Sorry for the million questions I just sort of expected to see some smoking gun type deal in the head.
 
Sort of interesting though, with the heads off i can freely spin the flywheel now with little resistance. May be due to the pb blaster i squirted in there.
 
Engine was apart once already.----At least one piston is marked with 0.030 for an O/S piston.-----How many are marked with 0.030 ????
 
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