1956 Mark 25 Fuel/Oil ratio.

[I B Dead Eye]

What is the Gas/Oil ratio for a 1956 Mark 25 using TC-W3 motor oil? I'm seeing 50:1 but that seem a bit much compared to my 54 Johnson at 25:1.[FONT=Roboto, arial, sans-serif] ??? [/FONT]

 

[racerone]

Well, 50:1 is less oil than 24:1-------------If and when I get my Mark 25 restored and running it will be 50:1------------When it comes to oil and gas mixtures the ideas and opinions are all over the map.

 

[Scott Danforth]

i thought the mark 25 was 24:1.

 

[MarioTwins]

2 stroke oil has come a long way since 1956. Most oils I buy now (chain saw weed eater ect) state on the bottle that 50-1 is fine in everything. I usually air on the side of caution and go a little extra lol. So maybe 40-1 and use it in everything. Even in my kicker when I tested it.
But results may vary.

 

[DeepCMark58A]

I run my 1961 at 50-1 Quicksilver oil only.

 

[jimmbo]

The ratio for engines of that era was 20:1. During the early-mid 1960s Mercury introduced their Formula 50 oil. They recommended it at 50:1 for engines built after 1962. For the engine built prior to 1963 the recommended Their Formula 2 oil at 20:1. I remember seeing a service bulletin from the 1970s saying the 50:1 could be used in all engines a 50:1 because mercury had always been a full roller/ball/needle bearing engine. http://www.boatinfo.no/lib/bulletins.html#mercury-service-1980_06

 

[Chinewalker]

I run all my classic Mercs at 25:1, save for racing motors, which I fatten up to about 16:1. Oil is cheaper than pistons on these old beasts. They generally have very loose tolerances and the extra oil does more than lubricate - it seals. The center mains on the '50s Mark 25s are a brass bearing as part of the reed cage. They like the extra oil to keep the crankcase halves sealed...

 

[jimmbo]

Those bearings/labyrinth seals/reed cages were used well into the 1990s using 50:1 ratios

 

[Chinewalker]

With the exception of some 1955 reed cages, most Mark 25 cages were a solid bronze bearing surface, lacking the oil catching grooves of the later reed cages. The earliest Mark 25s had a needle bearing and sleeve arrangement, similar to, but not the same as, that used in the Mark 20H racing engines.