Mercury KF7 rusted tight powerhead

[green-thumbs]

Acquired a "GIFT" Mercury kF7. I have stripped powerhead down. It is stuck tight with no slop
Intake ports show rings rusted, 3 of 7 exhaust cover screws will not budge
Advice on where to go from here would be appreciated.
If nothing else I would like to remove pistons as the little I can see of them seems ok.
I have used grease gun in past on earlier models with mixed results.
Louis
I am tempted to chuck motor into a vat of boiling water for lack of a better plan..
The tower and foot seem pretty decent.

[dave-bernard]

I may have a powerhead you can use call me 1 914 310 7086.

[green-thumbs]

Thanks for the offer. I have no immediate plans other than to get powehead apart while doing as little damage as possible..

The basic problem of what techniques work best to for a stuck KE7,KF7,KG7 or KG4
still remain. I do know that exhaust cover screws are known to snap off…leave them
alone for present. I would appreciate any insights from those more experienced
with stuck powerhead of a motor in this series.

Lacking any better ideas I probably will try grease gun. From what I can see and conditions
so far encountered it is likely that both pistons are stuck by rusted rings, upper and lower
rod bearings seized with rust and same for crankshaft bearings. I am hoping that careful
gentle efforts will salvage whatever can be saved. Worst case all junk and wasted time
and material.
Thanks
Louis

[mr-asa]

I prefer to initially use a fluid that will seep in and penetrate into the rings. Transmission fluid and gentle heat usually does it for me. I generally try to plan on doing the easiest reversible course of action first, if you went with grease first you would be hard pressed to get it out enough to let everything in to soak.

The next one I get that needs it, I plan to get about 3 gallons of this stuff and toss it into a 5 gallon bucket along with the powerhead. It dissolves oil, carbon, and somehow transforms rust back into normal iron/steel.
http://www.berrymanproducts.com/product … s-cleaner/

[20mercman]

If the rings are above the ports so the cylinder is sealed, then I would use the ATF and acetone mixture and fill it up and let it soak. I have a spark plug end that I welded a zerk fitting to and I add a pump of grease to it. This will force the ATF/Acetone mix down to the rings. I let it sit for a day, then give it a few more pumps. If the piston is down below the ports, the old tractor folks use wax to seal up the ports first and then fill it with penetrant.

Steve

[chinewalker]

I went through a KF7 early this spring with a very tight powerhead. After numerous attempts at soaking with various elixirs and gentle tapping with dowels, I ended up sacrificing the crankcase to salvage the block and crankshaft (I had another crankcase on hand). At some point the desire to save every part has to be weighed against the ability to do so, safely and within a suitable amount of time. In the end, I got a good crankshaft, one good piston, and the block. These were all put to good use as I got it running a couple weekends ago!

[20mercman]

I have been pretty lucky getting motors apart that have been pretty stuck. I did have a pair Mk-25 blocks that I resorted to sawing the connecting rods off as I had tried everything to get them apart. I soaked it for over a year! As crazy as it sounds, I was able to salvage one crank and one crankcase. The blocks had severe pitting that would need a sleeve to repair. I finally used a hydraulic press and it took over 9,800 lbs. of force to get it to move! These had been left outside behind a shed for years. Other than those, I have been able to free up over a dozen others that are now running, several using the grease gun method I described. If you have time, let it work.

Steve

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