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1990 90hp VRO bending spark plugs

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pugetsounder

Advanced Contributor
"Posting this for a friend. He

"Posting this for a friend. He bought the motor about 6 months ago. The compression check showed pretty good in all four within 10% three exact, one about 10lbs lower. Ran great, smooth, starts up no problem. The oil pump was working fine. He spent a couple of days out on the water and everything ran great. Then this past weekend on a boat camping run it starts to lose power. Still ran but only on three cyls. Limped it back to the dock. Took it to a shop and they pulled the plugs to find one tip squished closed. Put in a new one, started it up, ran good for a bit then the same thing. Pulled the plug and it was squished close again.
Any idea what could cause this? It's not noisey or any knocking or any different sounds. Is it fixable without a complete rebuild? I'm a stern drive guy and to pull a cyl would involve pulling the leg, pulling the motor out of the boat just to get to it. But the OB looks pretty easy to pull the head and get to it to see what's up. I have access to cyl hones, ring compressors, etc, if the piston assembly needed replacing. Is this a pipe dream or relatively simple? If he could just get a summer out of the motor would be a world of help. Right now he's thinking he's got an expensive boat anchor. Thanks for the advice."
 
"he would be right,on the anch

"he would be right,on the anchor thing....until fixed..he has got a big prob.....bad/missing bearings,loose rod cap,broken piston pin area,would be my guess...needs overhaul.u remove the pwrhd from exhaust hsng,to rebuild."
 
"I was afraid of that. How har

"I was afraid of that. How hard would it be to pull the piston and connect rod of the cylinder in question? Do I have to pull the crank or can I push it through the top deck. I was thinking if the cyl walls aren't scored and the crank journal isn't damaged just replacing the piston, rod and bearing and head gasket might fix it at least for a while. Like I said there is no knocking sounds or anything like that. Does anybody have an exploded diagram of this motor online somewhere? Thanks again."
 
"First, make sure you are usin

"First, make sure you are using the right plugs! If I remember correctly, those plugs should have a relatively short threaded section."
 
"Thought of that but all four

"Thought of that but all four are the same and it only happens on one cylinder.

I found this diagram:

http://www.boats.net/parts/search/BRP/JOHNSON/1990/J90TLESB%201990/CYLINDER%20&% 20CRANKCASE/parts.html

Am I right in assuming there are no crank shaft end caps? The entire bottom casing of the motor holds the crank in place? That would make things way more complicated. I've replaced a rod and wrist pin bearing in a car before just by pulling the the head and oil pan off and having complete access to the crank and piston. It ran when I sold it quite a while later no problem. But outboard 2-strokes are a pretty comlicated animal even with the easy access."
 
"good point---correct plugs ar

"good point---correct plugs are--QL77JC4---if using the wrong plugs,it would be doing it on all cyls ,however."
 
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