Vintage Mercury Cooling Issue

[racerone]

There was a plastic washer installed at the factory.-----On top of the water tube.----On severe overheat it could melt and block waterflow.----Factory replacement ( have them on hand ) now is phenolic.----

 

[tpenfield]

There it is . . . One melted piece of plastic.
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I'll be ordering a new powerhead gasket and whatever the thingy that replaces the plastic. Would an o-ring work?

Looks like this motor may be saved.

 

[tpenfield]

Quick Update . . .

I got the (melted) plastic seal replaced with the phenolic version and a new gasket. Also cleaned up some of the water passages. The powerhead is back on . . . Still more bits and pieces to assemble.

I think I might try to run some water through the cooling system via the copper tube before proceeding, just to make sure there is good flow.

 

[tpenfield]

Update . . .

The cooling system test went OK and I assembled the rest of the motor today. Here it is running once again, now with a healthy telltale stream.
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So, (hopefully), I am all set for next season

Thanks @racerone for your tip on the plastic piece (that melted). That was clearly the issue and may have been that way for a while.

 

[racerone]

Learned about this issue 40 years ago.-----All simple to me now !

 

[Scott Danforth]

Update . . .

The cooling system test went OK and I assembled the rest of the motor today. Here it is running once again, now with a healthy telltale stream.
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View attachment 372930
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So, (hopefully), I am all set for next season

Thanks @racerone for your tip on the plastic piece (that melted). That was clearly the issue and may have been that way for a while.

Ted, is this your definition of a Wicked Pissah?

 

[tpenfield]

Ted, is this your definition of a Wicked Pissah?

Yes, it is a wicked pissah

Just glad to have the motor back running.

 

[tpenfield]

Quick update . . .

I started the Mercury up in a test trough to make sure it was good to go for the season. The cooling system gremlin quickly re-appeared and I think that I'm running out of options to get it to be reliable (enough) as the main engine for the dinghy.

I put it up on CL as a parts engine, as I thought that might scare it enough to start cooperating

 

[tpenfield]

Quick Update . . .

The scare tactic worked. I was able to figure out a clog in the cooling system, the engine started cooperating, and I ran the engine for several hours today without problems. I checked various parts of the powerhead with my IR temperature gun. All areas around the cylinders are 130-160˚ F. So, I'll call it good.

So, the motor is saved for now. I'll try it on the dinghy next week. I have a 3 HP Yammy in reserve, but I really like how the 7.5 powers the boat.

 

[tpenfield]

Another update . . .

My efforts to descale the internal water jackets of the powerhead resulted in a fair amount of discharge of crud that was blocking the pee hole, and I believe causing the cooling problems.

What has worked with the cooling system is a modified 'pee hole' as the original one was getting blocked. I modified it with a much larger nipple, so it can readily discharge whatever may normally have clogged it.

It seems to be OK. I'll be testing it out on the dinghy soon to see if it is all good.
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It has plenty of flow from the water pump . . . so fingers crossed it stays that way.
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View attachment IMG_46481.mov

 

[Scott Danforth]

Looks like me after a dozen cans of liquid fishing enhancement

 

[jimmbo]

Those Red Decals are pretty much the Best that Mercury ever ever used on their Motors

 

[tpenfield]

The engine works . . . at least it cools fine.
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I brought the oars just in case and ran my 8 ft pram around from the house to the dinghy dock.

Got there just in time to see a launch ramp follies/fail. With the tide cycle this week being so low, a guy was having trouble getting his boat deep enough to float off the trailer. His solution was to unhitch the trailer and just let the rig go off the end of the ramp (OK ). The only problem was he had no lines attached to either the boat nor the trailer. The boat went one way and the trailer went another way . . . the guy ended up swimming after both.

The little Merc does not seem to like to go full throttle, so I'll have to see if I can sort that out. It could be old fuel, or maybe throttle linkage, but for now it gets the job done.

 

[tpenfield]

Quick update . . .

Engine cooling is fine on the little Merc, but it does not want to go above mid-throttle for some reason. The linkage, throttle, and ignition advance are going up all the way to WOT, but the engine happily goes about mid throttle (just based on the current sound vs. its historical usage.)

I'm thinking maybe the main jet in the carb is partially clogged . .

I suppose I can put my handheld tachometer on it to get am RPM reading.

Essentially, the way the engine is running, the boat goes at about the same speed as my 3 HP motor.

TIA - for any insight

 

[racerone]

Running on 1 cylinder.----First thing to do is a spark check.

 

[tpenfield]

Running on 1 cylinder.----First thing to do is a spark check.

Possibly . . . although it runs smooth, just not very fast. I am wondering if my IR temperature gun on the spark plugs would be a good indication if they are firing.

Meanwhile, I have been cruising through CL looking for its replacement.

 

[Scott Danforth]

There are a few on Facebook marketplace

 

[tpenfield]

@racerone . . . I am thinking that the engine is running on one cylinder. Being a 1969 it is a points ignition system. Wondering how involved it would be to switch to the coils?

 

[racerone]

Likely just need to clean the breaker points.----That is if spark is the issue.-----These motors are so simple to trouble shoot.-----Motors sold privately usually have issues as well.

 

[tpenfield]

Likely just need to clean the breaker points.----That is if spark is the issue.-----These motors are so simple to trouble shoot.-----Motors sold privately usually have issues as well.

Thx

I'll be headed to the boat dock this AM with some tools in hand. I'm hoping it is something simple, like Spark plug fouling or a wire fray. To get to the points/coil I believe I need to pull the flywheel IIRC.