I just got a 58 MK25 attched to a 1948 Feather/runabout. I know nothing at all about these. The goy I got it from said it ran perfect 2yrs ago and all it should need is a good cleaning and tune up.
Question is, was there anything that I should look for that they were prone to have happen? I really want to keep this on the boat cause it fits it so nice. What kinda performance should I get from it? The seller said he never ran it on this hull and that he ran a 18 Huricane on it and that scared him and that this 25 will be to much for the hull.
The Mark 25 is actually an 18 HP, 20 ci Merc Hurricane powerhead.
They can be made to idle well and blow the socks off any 18 HP OMC, etc.
The face plate appears to be from either a 1955 or 1956?? Mark 25, but the driveshaft housing, and everything else could very well be a 1958.
Their weak points are:
1) A steel driveshaft & prop shaft that can cause seal failures, resulting in water in the gear lube.
2) It probably should have a new impeller installed, but they are getting tough to find.
3) The ignition coils typically can become damaged from ambient moisture. If their coating is cracked open here-n-there, they will need to be replaced. Fortunately they used Phelon coils (Phelon magneto), and the coils are still available.
Up here in the great Pacific Northwest (western Washington State)ambient moisture is a constant threat to internals of any engine that has not been properly fogged before storage. It can etch the crankshaft, connecting rods & their related bearings, and the main bearings.
I had to tear down (4) Mark 25 power heads to find (2) good rods and a good crankshaft.
Other parts of the country may or may not have these issues??
The Mark 25 is one of my favorite Mercs.
Thanks Doc, good info. He had one like that with the starter but I figured this hull is so small I didn't want a battery taking up room or weight.
He also has a MK30E that I hope to get from him for my Jet Streak can't remember the year but it is a very cool pastel blue with a perfect blue face plate and the heavy SS cowel cover.
On the 25, any tips on tuneing it so I don't have to kill my arm yanking that rope? LOL, not looking forward to that seeing is I am older that it.
Oh, almost forgot! I/he was wrong on the year, after cking the #s its a 56.