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I WOULD LIKE EVERYONES THOUGHTS ON THIS

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navchapdoc

Member
"Here are the facts..1994 90HP

"Here are the facts..1994 90HP Merc. Top and mid cylinder at 115 and 105. Bottom hole at 80. I took the air box one day and found a small puddle of gas/oil in the bottom carb throat, last time I took it out at 5000rpm the overheat alarm went off until I took it down to 4000 or below. Runs pretty well over all. Seems to smoke a bit more than I think it should when being flushed out in my yard. Here is the question...Could this low clyinder be a bad head gasket?? The plugs were changed just before I bought it so I dont know what they looked like. The carbs are being rebuilt completly this week. My Mech said the reeds looked good. The cylinder head where it meets the block looks good, no sign of corrosion. Could this be something other than a piston and ring issue??? I was thinking about the gasket cause of the overheat thing at 5000. The pump and impeller are new, so is the sending unit and poppet valve so I know water is flowing
Thanks alot!
John"
 
"It doesn't have a cyl hea

"It doesn't have a cyl head. It only has a water jacket cover, the head is the block. You need to remove the intake or exhaust covers as mentioned to determine whats wrong. Buy a manual and save the money by doing it yourself. It's more labor than parts"
 
"John, most Merc's includi

"John, most Merc's including yours are "headless". What you note as the "cylinder head" is actually just the water jacket cover. No compression will leak out of that. If you pull that cover you will note that the cylinder is complete inside of the top of the block with the only access to the "outside world" being the hole for the sparkplug.

Because of that, odds are that you have bad rings or you have scored or damaged the cylinder wall itself.

Unfortunately, unlike other makes where you can pull the head and get a look, you can either pull the exhaust cover and peek inside or you need to tear it down and split the block.

It kinda does sound like you had a clogged carb which resulted in a lack of oil to the one cylinder, which did "who knows" what damage, coupled with an overheat which certainly didn't help the situation.

You are best to address all your issues right now while the motor is rebuildable. Continued use in it's current state could result in you turning it into 300 pounds of scrap aluminum..."
 
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