Mercruiser 470 repower 1978

[surchin]

Got the boat back today and took her for a run at sunset after work and the new plumbing is working fine

Engine runs cold at 100 deg or so. Flush the system at the ramp after coming in and seems to be working fine. I've learned most of the commercial fisherman here run open coolant systems like this they run their boats all day in kelp and raw water keeps the engines much lower temps.

I did notice a small dribble of a leak between the head and the block. Slight drip of water down the outside of the motor I didn't see it before as it was behind the heat exchanger not sure if coolant would have leaked from there. When it would boil over out the cap it would not have been possible to see it.

Anyway. Glad to get the boat back with a quick and cheap fix. Maybe not how the motor was designed or the best technical fix but I ll see how it goes. Maybe someone else can benefit from my trials here.

[surchin]

My rig


They are good looking boats.

[Destroyer]

A harmonic balancer is, basically, a vibration damper. When an engine (any engine) runs it vibrates. The crankshaft harmonic balancer is a device connected to the front of an engine's crankshaft, usually built into the crankshaft pulley. It's usually made of rubber and metal, which easily absorbs any harmonic vibrations that could harm the engine otherwise. Look closely at most balancers and you'll see that they are made of an inner metal mass, then a rubber ring, and then another metal mass with groves in it (the pulley). To further explain in far better language then I could muster here is a quote from Wkipedia on how they work.

"Each time a cylinder fires, the force of the combustion is imparted to the crankshaft rod journal. The rod journal deflects in a torsional motion to some degree under this force. Harmonic vibrations result from the torsional motion imparted on the crankshaft. These harmonics are a function of many factors including frequencies created by the actual combustion and the natural frequencies the metals make under the stresses of combustion and flexing. In some engines, the torsional motion of the crankshaft at certain speeds can synchronize with the harmonic vibrations, causing a resonance. In some cases the resonance may stress the crankshaft to the point of cracking or complete failure. The harmonic balancer helps minimize torsional crankshaft harmonics and resonance. The damper is composed of two elements: an inertia mass and an energy dissipating element. Most often made of rubber, this element may be composed of a synthetic elastomer, a clutch, a spring or fluid. The mass counteracts the torsional crank motions and in concert with the energy dissipating element absorbs the harmonics vibrations".

So you see, by absorbing most of the harmonic vibrations being imparted to the crankshaft by the detonation of the air/fuel mixture in the cylinder the balancer extends the life of your engine. Pretty smart these engineer type people. <grin>

[surchin]

All this time I thought it was a guy standing on one leg playing the blues
Doh!!

[step up here]

Good for you! just watch out for a hydraulic lock if its leaking into the cylinder.

[cfelton]

Sounds like you have a few issues going on. The head gasket probably needs replacing and resurfacing or replacing the head will help it seal better. If you do it check and clean out your exhaust manifold really good and check and or replace your riser. Seen a lot of good running motors ruined by overheating and bad rotten risers and clogged manifolds.

[aussie]

Sounds like you have a head gasket leak caused from a corroded head or block could be only gasket What you have done may work but all it will do is cause the leak to get bigger quicker .Yes your engine will never get hot now and long as you know that when you have water problems from leaks out of the block you wont be able to fix them.Also all that sealer you put in the cooling system will no longer seal what it use to as the salt water is affecting it and the leaks you have may of started because of that..I would keep a eye on it all the time as it may get worse and start filling your hull with water make sure you have a working pump lol

[Destroyer]

Originally Posted by aussie

Sounds like you have a head gasket leak caused from a corroded head or block could be only gasket What you have done may work but all it will do is cause the leak to get bigger quicker .Yes your engine will never get hot now and long as you know that when you have water problems from leaks out of the block you wont be able to fix them.Also all that sealer you put in the cooling system will no longer seal what it use to as the salt water is affecting it and the leaks you have may of started because of that..I would keep a eye on it all the time as it may get worse and start filling your hull with water make sure you have a working pump lol

X2

[surchin]

Hey guys OP here .... thanks for the input. It’s 4th July 2018 and so far so good with the merc. I was hoping to get another year out of it and things seem to be running well. I use it pretty regularly at least 1-2 times a month to keep it going. The overheat was just such a bust I would recommend a raw water bypass to someone as last resort.

My theory is that I had a small leak behind heat exchanger between block and head that was causing loss of pressure and it would boil over. Couldn’t see it with heat exchanger mounted. And fluid coolant boil over masked the leak.