is this common?

[spamreef]

I have an 1980s 80 hp 4 cyl mercury.It ran verry well a few years ago but over the course of last summer it started to run rough and loose power. after looking at it the service shop said it was the ignition systen ,and replaced it. This did not help at all. so i did my homework and took a look at it. i found everything to be in good shape. the only thing i could find wrong with the motor is that the bottom spark plug is very very clean witch tells me that water is getting in that cyl. i did a compresion check on the top 3 cyls. ant they wear fine, i was not able to take a reading on #4 because the cowl is in the way. does this sound like a gasket? or is this major engin damage? I have heard thats its commom for #4 cyl. to collect water when the boat stops ubruptly,,, is this true??? thanks scott

 

[Texasmark]

Re: is this common?

Wish I could help, but haven't a clue.<br />Mark

 

[Clams Canino]

Re: is this common?

Lower crank seal *might* be bad - allowing water into bottom one. However, bottom plug often gets a litle steam cleaned with no malfunction at all present.<br /><br />-W

 

[Chris1956]

Re: is this common?

Spam, I put a 90 degree elbow on my compression guage. It just fits the bottom cylinder, and allows a compression test.<br /><br />As for the water intrusion, if it is not seals, it could be that either exhaust baffle has a leak, or inner exhaust cover has a leak. Hopefully it is just the lower crank seals.

 

[spamreef]

Re: is this common?

thanks

 

[DHPMARINE]

Re: is this common?

It probably should have gone back to the shop that did the ignition work.You paid them good money,and 'it didn't help at all'.<br /><br />A couple of ideas: (besides the above)<br /><br />Do a manual 'test' of compression.Hold your finger or thumb over # 3,then over # 4.Are they similar? If very different,yes you have a compression problem.<br /><br />Look for h2o on the plug.Connect the motor to a flushette and crank with the #4 plug out.If you don't see water,maybe that's not your problem,either.<br /><br />When I see a clean (very very )spark plug,it's no spark,and the gas is washing it down.<br /><br />Water beads,gas doesn't.<br /><br />DHP

 

[spamreef]

Re: is this common?

good ideas all the motor devloped a noise (clanking) when i was tinkering/running/testing it i suspect that the clean plug meant water in #4 and that the noise was due to the water washing the oil off the bearing and damaging it. but i guess if #4 was down for some time that wold also cause stress to the bearing? any thaughts?