50:1 or 24:1 Oil Blend???

[PistlePeat]

I have too many outboard motors to keep track of...LOL. They range from a 1947 Martin 60 and a 1951 Johnson 35, to 1970's and 1980's vintage Evinrudes. The latter ones all call for 50:1 oil, while the 2 older ones were originally designed for 24:1, whaich is what I've always used. Naturally, it would be simpler to use 50:1 in all of them, using Merc or OMC quality 50:1 oil of course.<br /><br />My question is...if I use good 50:1 oil, will the 2 older ones be OK with that blend. If I need to stick with 24:1, should I use 50:1 oil or some other type?

 

[JasonJ]

Re: 50:1 or 24:1 Oil Blend???

Stick with 24:1, those motors have bronze bearings that need a certain micron thickness of oil for proper lubrication. The 50:1 motors are on roller bearings so they can run with less oil.<br /><br />My kicker is a 57 Johnson needing 24:1, and my main is a 69 Merc needing 50:1. I just deal with it.<br /><br />There isn't such thing as a 50:1 type oil, that is just the ratio of gas to oil. Any of the oils are fine, I personally use Penzoil Synth blend with good results and good cost.

 

[PistlePeat]

Re: 50:1 or 24:1 Oil Blend???

Around the time that the switch was made to 50:1, the engine manufacturers specifically touted their own brand of oil saying that it met the requirements for 50:1. Their manuals stated that if you used another oil, it should be used at 24:1. At the time i had a lot of Texaco outboard oil, and I continued to use that at 24:1 per my owners manual. Even today, in my chain saw, the manual calls for a specific grade, and says to use double if its not available. I always thought that the switch to 50:1 coincided with more than just a change in the motors, but that the oil was improved as well.

 

[Paul Moir]

Re: 50:1 or 24:1 Oil Blend???

There's no doubt that TC-W3 is superior than anything sold in the '50s and '60s. But I think you'll find there's good reason that almost all the 50:1 engines have full roller bearings everywhere inside the engine while the 24:1 engines often don't. And even the few that did have plain bearings that OMC said would run 50:1 (the very smallest engines) don't seem to last nearly as long as their older, 24:1 rated counterparts. Finally, there's the evidence that every modern 50:1 engine uses frictionless bearings throughout.<br />You really see this in the cheap off-brand engines that didn't get full rollers into the 70s. They were rated at 32, 24, and sometimes 16:1. I'm sure if their manufacturers could switch to 50:1 they would have.<br />An important role that's overlooked with older engines and the ratio of oil is sealing the crankcase. A lot of those engines use the oil itself running through the plain crank end bearings to seal the crankcase rather than proper oil seals. <br /><br />PS - I noticed you said a '51 35hp. '51 would be the introductory year for the 35.7CID "Big Twin" but it was rated at 25hp. In '56 it was developed into the 30hp and then in '57 it was made bigger (40.5 CID) as the 35hp. A number of those engines only run plain bearings on the rod ends and have proper oil seals, and a few here run them at 50:1 (at their own risk of course).

 

[BoatBuoy]

Re: 50:1 or 24:1 Oil Blend???

Paul,<br /> I don't mean to hijack, but I'm confused. I certainly know what a roller is, but what is a plain bearing?

 

[Silvertip]

Re: 50:1 or 24:1 Oil Blend???

The rod and main bearings in your car are plain (insert style) bearings with no rollers, needles or ball bearings. Bronze (plain) bearings are a simple chunk of bronze with a hole drilled in it. Porous bronze is used in appliances, lawn mowers, and other applications. Oil is forced into the bearing under heat and pressure. These are commonly known as oilite bearings.

 

[Paul Moir]

Re: 50:1 or 24:1 Oil Blend???

Most the J/E engines had phosphor bronze plain bearings (no need for porous bronze as oil is provided). Except the later 5.5 and 7.5hp engines which had silver plated ones on the con-rods which I suppose worked better. The 7.5hp had gained quite a reputation for breaking con-rods.<br />There's another name for plain bearings but I can't seem to remember what it is. EDIT: Sleeve bearings?

 

[BoatBuoy]

Re: 50:1 or 24:1 Oil Blend???

I know exactly what you're talking about now. I just wasn't used to the term plain. Was babbitt ever used for the bearings?

 

[Paul Moir]

Re: 50:1 or 24:1 Oil Blend???

Yeah, that's the word I was looking for. Babbitt is the general name for the metal that the bearings are made of. I think technically it means a tin based bearing metal.