Reply To: 1957 Merc Mark 25 not warming up

[GUY SCHMIDT]

jeff-register wrote:

Guy,

I had cooling problems with a KF5 very similar to the mk 25. I pulled the water jacket cover off the cylinder, has no head., very carefully, the bolts break easy, used a  torque wrench, using max touque in rweverse as to not use excess torque rating & a little heat on  the cylinder threads& panther piss to loosen to get them out.

then used anything that woulld fit in the cylinder cooling passage to scrape the surfaces clean then hose out & removed a large amount of junk from the area. Next I reversed thru the water release hole where the discharge  is to clear that passage, then put back the water jacket cylinder cover. NEVER scrape the cover or cylinder top as it will leak if you do. Install new fasting  bolts or studs so next time you  remove only nuts to service, MUCH easier, use stainless studs & steam pipe thread lubercant, comes in a small tube like toothpaste to insure removable, looks silver paste. The  water exits from the wateer pump up a copper pipe up the   leg to the water passege into the exhaust cooling side cover & fills that passge then the cylinder cooling area then exits thru the exit passage & a weep hole inside  the leg to cool the exhaust. Very important to keep the bottm crankshaft seal good as the water exit is next to exhaust outlet. The seal is placed downward so inportant because any unburned fuel inside the crankcase is pushed out into the leg to keep from fuel collecting in the crankcase. I also have seen broken  blades  from  the waterpump stuck  in the watertube in the leg so it would impede water flow, Also on some watertubes the bottom cut were cut flat & if they vibreae down very little & impede water flow. Mercuy found this mistake early & started cutting the water tube at a 45 degree angle.  It’s worth it to pull the powerhead, replace the base gasket & bottom crankshaft. You will know if the top crankshaft is bad as fuel vaper will soak the mag & no spark. If you do the top seal , (I would) Get a pitman arm remover & dremel it to fit the magnetic rotor to remove the roter to remove the magneto plate to get at the top seal, two screws going sideways for plate tension. Clean & relube friction surfaces, use an inert light grease. Crankshaft seals are like shoes, never install one, do the pair! Your idiling will  improveSO much & save your rod bearings from sucking discharge water into the crankcase!!! P.S. The drawing shown is for OMC (Evinrude & Johnson motors). Mercury has no head or gasket, only a cooling waterjacket cover. The pistons install from the crankcase up because the cylinders0n were machined as one piece. I guess because of high compression Carl thought they would blow head gaskets, so he made them one piece & resolved the possable problem, in my opinion. Who’s Carl??? anyway?

 

 

Good luck

 

Thanks, I didn’t see your message earlier and wasn’t on line for a bit. Great info.