1990 90hp, leaking outer exhaust cover; low compression

[funpilot]

My sons reported that the boat wasn't running like it should, I finally had a chance to put it on the lake today. It did run poorly, and with the fast idle lever up I could only get about 1200 RPM. I ran it around, it sounded rough, got about 5000 RPM out of it tops. There was water coming out of the engine in a pretty good stream by the lower side of the starboard cylinder bank, at first I thought it was a bad head gasket.<br /><br />I took out the sparkplugs and did a quick compression test (not WOT) and got about 40psi on the upper starboard spark plug (#1?) and a good 115 psi on the rest. I was expecting the lower starbord (#3?) to be low, so I ran the engine on the muffs and found that the exhaust cover plate is leaking from its gasket close to where the tube for the indicator stream is taken off the exhaust cover fitting, and not the head gasket. It's just spraying in the general direction of the head.<br /><br />So, I have two problems. The first is replacing the gaskets under the exhaust cover and the second is determining what is wrong with the compression. I see a rebuild in my future, and reading the clymer manual makes it seem that this rebuild is going to be a lot harder than the 120 hp Sport Jet (Force/Mercury) engine I did last.<br /><br />Except for replacing both plastic bowls with metals ones, and a new clutch dog and reverse gear, this engine has been very reliable for the past 15 years. Just regular decarb, lower unit fluid, spark plugs and fuel hose repair.<br /><br />Any comments on what I'm seeing, would be appreciated.<br /><br />Thanks,<br />fp

 

[Goodoleboy]

Re: 1990 90hp, leaking outer exhaust cover; low compression

Sorry to hear your compression is gone. I would guess its broken rings.<br /><br />You will want to determine what caused broken rings before repair is made. Otherwise repair job may be useless.<br /><br />Good luck!

 

[Goodoleboy]

Re: 1990 90hp, leaking outer exhaust cover; low compression

I supose you could just have a blown head gasket. I guess you will know for sure when you pull the head.<br /><br />Good luck!

 

[funpilot]

Re: 1990 90hp, leaking outer exhaust cover; low compression

Thanks Goodoleboy,<br /><br />I just looked at a rebuilt powerhead from iboats. I don't think I can tear the engine down and rebuild for that. Anyone have experience with buying a powerhead? The rest of the outboard, lower unit, etc, are good.<br /><br />fp

 

[Dhadley]

Re: 1990 90hp, leaking outer exhaust cover; low compression

Buying a replacement is a very logical way to go. All you have to do is undress yours and redress the new one. Youll still want to do the usual stuff, clean the carbs and replace the water pump. The biggest thing is to determine why it did whatever it did and fix the cause of it.<br /><br />A damaged piston is a result, not a cause.

 

[funpilot]

Re: 1990 90hp, leaking outer exhaust cover; low compression

Thank you Dhadley,<br /><br />I replaced the water pump last fall just before storing, and it seemed to run fine, good water stream from indicator, and no warning of overtemp. In fact, I only replaced the impeller as a matter of maintenance. Started fine, ran fine. Each year I've decarbed it, and put sea foam in the fuel tank and fogging oil in the engine via the shraeder valve. I happen to have indoor, heated storage for my boats.<br /><br />The motor has been used hard over the years, probably weekly or more until the past two years since my sons have moved away. Now it is more like monthly use. I had the boat out a week or so before my oldest son came home, and it ran fine. I didn't notice the water leakage from the exhaust cover, in fact, never suspected such a thing was probable. It has been using oil from the VRO tank as it always has, all summer.<br /><br />If I buy a replacement power head, would it be acceptable to remove the head and look inside before I ship it off? The carb rebuild is a good idea, are there any other typical areas to look at when a piston goes bad?<br /><br />thanks again for your thoughts!<br /><br />fp

 

[Goodoleboy]

Re: 1990 90hp, leaking outer exhaust cover; low compression

What was your WOT rpms. Most all the top wrenches on this forum say to have setup to turn 5800 to 6000.<br /><br />Dosent mean you have to run it this way all day long . It just means it should be abel to turn these rpms . <br /><br />Otherwise engine is "luging" which will lead to coking of rings. Which inturn will lead to broken rings.<br /><br />But theirs a number of other things that will cause broken rings also. Running to lean, running to rich.<br /><br />I wouldnt think it would matter if you pulled the head on engine prior to sending it in for replace ment.<br /><br />Like I said, It may just be a blown head gasket. 25 dollar fix.<br /><br />Good luck!

 

[funpilot]

Re: 1990 90hp, leaking outer exhaust cover; low compression

At the risk of opening a new can of worms on prop sizing...<br /><br />I was running a 19 pitch prop on this thing from day one, first an aluminum and then a Stainless. As my kids got bigger, they complained about being able to get up behind it. I asked my boat store, and they said I should be using a 17 pitch... and they sold me one (funny how the boat came rigged with the 19). That lowered my top speed for any given RPM about 10%, but improved the hole shot.<br /><br />I don't think I've ever seen 5800 RPM, at the most about 5500 with the 19 ptich and I'm not sure what I've seen with the 17 pitch.<br /><br />I thought I was safe from ring damage by decarbing the engine each year...<br /><br />Thanks for your viewpoint, Goodoleboy<br /><br />fp