spark plugs - 5 dirty, 1 clean???

[sergioy]

I was doing my mid-boating season oil and spark plug change last night and found something that kind of concerned me. I have a 1975 Mark Twain with a 165 hp I/O runabout. While changing the spark plugs I found that the very last one (stait 6) was perfectly clean, The other 5 where black. Should I be concerned about this, or is it normal? I have been pulling tubers and skiers like mad all season long and never had any problems with power.

 

[KaGee]

Re: spark plugs - 5 dirty, 1 clean???

Seriously, you may have stumbled upon a problem just starting. An absolutely clean plug is indicative of water in the cylinder. You most likely have the beginnings of a manifold/riser/gasket leak. More investigation is required.<br /><br />Just shows ya why up-keep on these things is so important. If you were not doing this you would not have found out until maybe too late and you did major damage to the engine.

 

[Scaaty]

Re: spark plugs - 5 dirty, 1 clean???

Kagee has this nailed. When were the exhaust manifolds last done? Also would not hurt to do a compression check to make sure its not a head gasket., What has happened is the same as steam-cleaning a sparkplug....you MUST find the source of water before that boat goes out again. Check to see if that old oil was in any way milky too. Good Luck

 

[sergioy]

Re: spark plugs - 5 dirty, 1 clean???

The oil was a perfect shade of black.

 

[Don S]

Re: spark plugs - 5 dirty, 1 clean???

The water is getting into that cylinder, may be a head gasket. It's basically steam cleaning the plug and may not even get to the oil.

 

[Bondo]

Re: spark plugs - 5 dirty, 1 clean???

I Totally Agree with All the answers above,.......<br /><br />But,.....<br />Being that it's #6,.......<br /><br />I'd be looking at the Exhaust,..........<br />Rather than a headgasket........<br /><br />Tubing,+ Sking,......... Lots of starts,+ Quick Stops,....??.....<br /><br />When's the last time you Saw the Flappers..????....<br />What kind of shape were they in ??

 

[sergioy]

Re: spark plugs - 5 dirty, 1 clean???

Flappers <br />Whats that <br />Sorry, Idon't mean to sound so dumd, but I really don't knowwhat that is.

 

[Don S]

Re: spark plugs - 5 dirty, 1 clean???

The reason I don't think it's the exhaust manifold or riser leaking is the fact that to be that clean (Steam cleaned) the water would have to be getting into the cylinder during the intake stroke, and water in the exhaust manifold shouldn't be doing that while it's running because the exhuast pushes the water out the exhaust, not back into the engine. If it's just a small amount of water getting into the cylinder while it's running from bad head gasket or cracked head or block, it could still be firing, but cleaning the plug (and piston top and valves) at the same time.<br /><br />PS: The flappers slows down the water being sloshed back up the exhaust pipe when the engine is not running.

 

[sergioy]

Re: spark plugs - 5 dirty, 1 clean???

Since my exhaust goes thru the prop, would I still have flappers?

 

[KaGee]

Re: spark plugs - 5 dirty, 1 clean???

Yes, somewhere in the lower exhaust.

 

[Scaaty]

Re: spark plugs - 5 dirty, 1 clean???

Jeezz. seems Don and Bondo was burning the midnight oil on this one........do a compression check, and if all even (last 2 anyway) lay off the tubing and see if it blackens up. And my opinion on a boat being used for tubing is its extremely hard on the motor....it just is not set-up for the high load, half plane, start/stop operation. Just my opinion, but I am paranoid about my many motors.

 

[jlinder]

Re: spark plugs - 5 dirty, 1 clean???

Not to hijack your posting, but the question of flappers is interesting.<br /><br />I have not checked mine. I have a 1988 OMC cobra w/ 5.0L GM engine. Where would I find the flappers?

 

[rbezdon]

Re: spark plugs - 5 dirty, 1 clean???

They are in the exhaust system just below the robber hoses inside the boat that connect the exhaust risers to the Y pipe. I have the same drive and both flappers have fallen off and lodged in the exhaust and had to be reomved with the drive off. We found them during routine yearly maint of the u joints. Replacing them is a bit of a pain but not as much as getting the old ones out of the exhaust path if they are missing. Get a manual for this and they are pretty easy to find in the drawings. The only tools you'll need to check them are a couple of screw drivers to remove thoser big rubber hosesw. If they have not been replaced recently, sometimes it takes a bit of struggling to get them off. Flappers cost is the range of $50.

 

[achris]

Re: spark plugs - 5 dirty, 1 clean???

These engines are very prone to cracking heads. they crack across the valve ports. Unfortunately, because they don't have a cooling system that you can pressurize, you'll need to remove the head to check it. Even if it is only a gasket, you'll still have to remove the head. So, out with the spanners. Don't be to concerned, this are one of the easiest engine to pull the head off.<br /><br />Chris...............

 

[achris]

Re: spark plugs - 5 dirty, 1 clean???

Here's a picture from the parts manual of the exhaust pipe, from riser/elbow to bottom of transom plate. The shutter is #7 in the diagram. V-engines have 2 shutters, one below each elbow. Earlier Mercruiser V8s have the shutters at the very bottom of the (3 section) pipe.<br /><br />

 

[rbezdon]

Re: spark plugs - 5 dirty, 1 clean???

AChris: There are two issues in this thread. This guy has an OMC 5.0, not a 4 popper Merc

 

[achris]

Re: spark plugs - 5 dirty, 1 clean???

vatter41,<br /><br />Appreciate your comment, but the original poster has an in-line 6 Mercruiser 165. That's what the picture is for. His third post in this thread asked what the flapper was, I have posted the picture to help him. The OMC V8 is another issue that should not change the original posters question.<br /><br />Chris..........

 

[Don S]

Re: spark plugs - 5 dirty, 1 clean???

That is exactly why people should start their own thread if they have a question, even if it's similar to another thread. They could refer to another post in their own post, but it just gets confussing with several questions by different people going on in one thread.

 

[KaGee]

Re: spark plugs - 5 dirty, 1 clean???

Amen Brother!

 

[jlinder]

Re: spark plugs - 5 dirty, 1 clean???

sorry, I was not trying to hijack the original post. It was just that there were people here talking about the flappers already.<br /><br />I will start another post. Apologies to water surge for any confusion I might have caused.