MERC 140 WATER IN #6 CYLINDER

[VMAX]

Hi all,<br />I have a 1979 Mercury inline six outboard that sometimes misses at low RPM's.<br />I pulled all the plugs to check them and found the #6 plug clean except for a milky white coating indicating water entering the cylinder from somewhere. Does anyone out there have experience with this problem?<br />I know that there is no head gasket on this engine, and I want to know where to look before tearing into the engine. Thanks, John

 

[denniz]

Re: MERC 140 WATER IN #6 CYLINDER

Run a compression test, make sure thats good if so its probably a exhaust plate on the port side of the block. If compression is bad you have bigger problems

 

[BIG GAZZA]

Re: MERC 140 WATER IN #6 CYLINDER

In addition to ROD's comment if it isn't the exhaust plate the bottom crankshaft seal has probably had it.

 

[VMAX]

Re: MERC 140 WATER IN #6 CYLINDER

I am not familiar with the "exhaust plate" leak. I assume that this is a cover between the water jacket cover and the exhaust ports-is this correct? If so, is this a common problem?<br />Does the leak occur at a gasket, or is there something wrong with the plate itself? In my manual, this looks like an aluminum plate.<br /><br />I also am at a loss about the lower crank seal leak. Is this to say that there is water pressure present in the area below the crank seal? This doesn't seem to make sense- please explain.<br /><br />Thanks for the help- John

 

[aeronutt29]

Re: MERC 140 WATER IN #6 CYLINDER

I'm going to assume that your powerhead is mostly the same as my '69 100 HP 6 cylinder. Having just finished rebuilding my powerhead, I'm intimately familiar with the innards. There is no way possible for water to enter the crankcase from the lower bearing cap. For one thing, there isn't a water passage that flows through that area. And for another, if water DID get pushed up against it there are two rubber seals and a giant O-ring that it would have to get past. <br /><br />I think the gasket under the exhaust cover plate is the first place to look. The bolts on mine where well corroded and required a lot of penetrating oil and patience to get out. The new gaskets and new bolts for the cover will set you back about $50. If you also want to pull the powerhead and replace the gasket that goes between the powerhead and the leg (just for good measure), it will take about 4 more hours of work. I would replace the gaskets in the exhaust cover first and see if that clears up the problem.

 

[denniz]

Re: MERC 140 WATER IN #6 CYLINDER

port side of block, 2 exhaust plates, check the gaskets and the plates.

 

[VMAX]

Re: MERC 140 WATER IN #6 CYLINDER

Thanks again for all the great help.<br />One thing I am wondering about though, Aeronutt.<br />You say IF I want to pull the power head...etc.<br />Don't I have to pull the powerhead off to get to the lower bolts on the side cover? It would be great if I didn't. Also, I have heard that a special sealer/adhesive has to be put on the cover bolts before reinstallation, does anybody have experience with this?<br />Thanks, John

 

[aeronutt29]

Re: MERC 140 WATER IN #6 CYLINDER

I don't think you have to remove the powerhead but you will have to remove the frame pieces that bolt around the powerhead to get the lower cowling to drop down a few inches. Once the lower cowling drops you should be able to get the bolts out. At least, that's the way my '69 works....<br /><br />Did you run the compression test yet? What were the numbers?

 

[VMAX]

Re: MERC 140 WATER IN #6 CYLINDER

Compression is 115 to 120 on all cylinders. I'll try the drop down the cowl trick. <br />Thanks, John