1980 Merc. 90hp I-6 water in #6 cyl

[glennwingman]

Whats the most likely scenario for why there would be water in my #6 cyl? Took the motor in for a tune up, had rust on my bottom plug. The boat starts and runs fine, except that it occasionally wants to be "choked" when applying throttle to avoid bogging. One quick tap of the choke button and it seems to flip into go mode, other than that, no problems. Shop tested the gas, found no water, so they want to rip into my motor to investigate...Any ideas of the best place to look? I tried a search, I apologize if I've missed anything...

Specs: 1980 Mercury I-6, serial #438-6952
Water pump is 1 yr old, and it pisses out the telltale hole every time it runs, although not as strong as my 76 650 merc did...

 

[Chris1956]

Re: 1980 Merc. 90hp I-6 water in #6 cyl

Normally water in the lower cylinder is from bad lower crankcase seals. These are located in the end cap on the baseof the block. the powerhead needs to be removed to get to them and replace them.

Another source of water is rotted out inner water jacket cover or exhaust baffle.

 

[glennwingman]

Re: 1980 Merc. 90hp I-6 water in #6 cyl

what am I looking at for time and difficulty replacing the lower crank seals? Ive read a few posts about the exhaust baffle ones, but the lower one scares me. Would I just need to lift off the powerhead from the leg with a hoist? It'd be a shame to let this problem go unfixed!

 

[Chris1956]

Re: 1980 Merc. 90hp I-6 water in #6 cyl

It takes about 1.5 hours to fix, I would think. Drop the gearcase. Disconnect electrical and fuel, remove cowling support and lowermost cowl (4 ss screws). Remove powerhead mounting bolts and lift block with block and tackle. Now loosen crankcase bolts near lower end cap, remove end cap screws and tap out old seals. Now reassemble. need new powerhead base gasket, but that should be all.

 

[glennwingman]

Re: 1980 Merc. 90hp I-6 water in #6 cyl

Ok, I was incorrect in my information that it was only the #6 cyl with water in it, I guess all 6 of the plugs had some evidence of water on them, so I now suspect water intrusion through the water jacket. I assume I no longer will be pulling the powerhead, and will instead look to replacing the three gaskets in the port side of the motor. Is there anything relevant or helpful not mentioned in the fsm regarding this job? Tips, tricks, words of wisdom from all of you seasoned inline 6 salts?

 

[glennwingman]

Re: 1980 Merc. 90hp I-6 water in #6 cyl

Spent last night taking the motor apart, removed all of the bolts and didnt break any, which was a relief. Had a heck of a time getting some of the lower ones, including the ones that secure the throttle and shift cable slides. Water was leaking in on the rear of the baffle in two places, and had left a noticable washout signature in the grease. Currently in the process of scrubbing the parts clean of their old gaskets and carbon buildup, as well as waiting for parts. My question is, however, can I expect a small increase in performance for removing all of this carbon buildup?

 

[Chris1956]

Re: 1980 Merc. 90hp I-6 water in #6 cyl

Doubtful, you will see any performance increase. Check the exhaust baffle for flatness. Carefully inspect the inner water jacket cover for holes. Did you remove it? Merc uses epoxy to install the inner water jacket cover screws.

If you have any doubt about the ability of the gaskets to seal, add some silicone to them.

 

[glennwingman]

Re: 1980 Merc. 90hp I-6 water in #6 cyl

From what I've seen so far, the inner water jacket cover is in great shape, I see no pitting or corrosion that would cause a leak? The water trail is very obvious inside the exhaust chamber where the gasket between it and the exhaust manifold plate baffle had failed, but once I get all of the old gasket material off ill be able to better look into any such issues. What grade of rtv should I use on reassembl? Id think blue would suffice for the baffle plate to exhaust manifold cover gasket, but im not sure if id trust blue for the water jacket cover gasket, there's quite a bit of heat there. Also, I've noticed the top piston ring on my #3 cyl is rusty (the only one I can see through the exhaust port) should I plan on doing a rebuild/re-ring these pistons soon? Doesn't seem safe...

 

[glennwingman]

Re: 1980 Merc. 90hp I-6 water in #6 cyl

new question: there is what looks to be an air line starting under my flywheel atop the #1 cyl, starbord side, running down behind my coils to the bottom of the motor next to the #6 cyl. Does anyone know what this is?

 

[Chris1956]

Re: 1980 Merc. 90hp I-6 water in #6 cyl

That is the bleed systems, such as it is. Any oil that collects in the lower main bearing is pumped up to the upper main bearing thru that tube.