All 2st Not another oil thread!

When talking about 2-stroke oils, usually things comes up like soot, clogging, smoke, ring sticking and so on. This time, lets talk about the relation between con rod big end lubrication and mineral / polybutene based oil

http://www.yamaha-motor.co.jp/globa...nical_review/publish/no35/pdf/0008.pdf#page=1

What are your thoughts about this?

"The higher content of polybutene in the oil is said to be essential to maintain the initial performance of 2-stroke engines. However, it is not so well known that this polybutene deteriorates the lubricity of the engine bearings"

"The polybutene based oil had crank pin temperatures 5 C to 30 C higher than the mineral based oil. And the difference in the temperatures increased as the engine revolution increased. Furthermore, when the polybutene based oil was run at 9000 rpm, the crank pin temp suddenly increased. (...) "

Instresting reading on the aspects of two cycle oil

In a "nutshell" that tells us we need a oil with good blend of polybutene to keep the exhaust system clean and a good lubricator, such as ester, to lubricate the bearings. Too much polybutene and you wash the lubrication away. Not enough and you gum up your power valves.

So about 500mw of polybutene and a nice synthetic ester with and a smidgen of mineral oil for good measure should do the trick.

Me either. In fact the only time I ever had to split case halves was on my '74 Suzuki TM400 about 30 some odd yrs ago, and that wasn't a bearing issue.
The piston was worn down so badly after several summers of flogging the guts out of it through the woods every single day without ever even thinking about cleaning the air filter, that the skirt was slapping the cylinder walls so hard that it sounded like a woodpecker. And it actually did that for a week or so before a chunk finally broke off and fell down into the crank case and got smashed through the bottom of the cases by the counter weights on the crank.
I was 16,...I mowed grass for bike gas money, and used $1.00 a quart Pennzoil 2-stroke oil I got at this little country grocery store.

Same here. But still, it is interesting. For the first time, I've got my hands on a street legal 2-stroke 360. According to some people, driving a 360 on the streets will kill the con rod big end. So, I started to look into the matter and stumbled upon this Yamaha study. I figured maybe those guys bought a too "racy" oil and then drove the bike way too careful, washing the lubrication of the bearings? I dunno... As said earlier, I've never killed a con rod bearing either.

@Motorhead: Making your own cocktail?

Oh I know,...and it is interesting,...and thanks for the info. And make no mistake,...I do put a lot of thought into running the best oil I can obtain. It's just what you do for the machine you love,...right?

I have my WR300 plated, (mainly just for dual sport rides) and I can tell you,...it doesn't seem to particularly enjoy a sustained constant road speed either. Here's my theory,...road riding most generally involves a lot of very low throttle openings at the upper mid-range of the RPM band,...especially with my 300 which is geared quite low.
Low throttle openings produce less lubrication to the engine internals, as well as a reduction in the cooling effect of the atomized fuel/air mixture to the piston and cylinder. My cylinder and head after 10 miles or so on a back road will feel much hotter to the touch than they ever do on the trails, and it will actually begin to border on developing a lean ping, (from heat induced pre-detonation) when it would've been as happy as a clam in the woods where I'd have been blipping the throttle intermittantly. This is the main reason I'm going to fatten up my pilot jet, even though it is jetted perfectly for off-road.

Now, that being said, the devil's advocate exception to my theory is the high dez boys. I don't know how they get away with that. I'm guessing their bikes would be jetted gurgling rich down in the deep tight twisty eastern woods,.....?

I always like to hear stories like that,...thanks big guy.
You know I've considered thickening my ratio back up to 32:1,...I broke it in on that per the owner's manual,...but geez it drools spooge at 40:1,...and it carburets crisp too. I know some guys like to see some spooge so they know they're getting plenty of lube, but I really don't need any more....

I have blown plenty of bottom ends. I've lost the big end bearing on the rod once, and nearly countless crank bearings. I have proclaimed myself Mr. Bottom end at one time. I was sick of splitting cases. I'm pretty good at it now though.

Just to answer the unanswered question. Bottom end jobs: Honda CR125, KTM 125, KTM 250 twice in six months, Gas Gas 250 (four times in one year).

I've run every kind of oil you can think of, from "Bean Oil" to Amsoil 100:1. I don't know if I'd say any of the failures were oil related, outside of running the Amsoil at 100:1 (yikes).

Holy cow Batman another oil thread!! We gotta nail this sucker But this is 2-stroke stuff we'll let it live and make the most of it...

Have you ever considered adding more oil to the gas? Going lean on the oil is just asking for the results you are getting... 3.5 to 4 ounces per gallon should be fine for most any modern engine. And I've used lots also..usually on the cheap side and my CR250 has a piston that is 7 yrs old. I don't consider the BS of changing a piston just because I rode it hard last year anything other than a myth such as changing oil every 3000 miles in my car...If your piston has not got any slack or your rings are not stuck..UR just wasting time and money and risking doing damage when you open it up.

I luv bean oil...it always identifies itself 100% about 2-3 seconds after it passes The one hard-asss guy I knew that used it in the '74 mixed at 3 ounces to the gallon in his 500cc yama-hammer and yep and burnt alot of pistons but was really fast before the burn

These things we call engines are just metal. No brains, no feeling, no opinions, just metal. Metal reacts in the same way always. Just physics in play. Metals heat up when rubbed together. Bearings are a good example. About 100 yrs ago, we discovered how to control this heat: pour oil on it. Too much, it drips off. Too little, we are back to square 1. Do the former here.

That is so true. I've lived on the statement, "how do it know?" I always run 36:1 ratio now. Mostly because that's a nice easy number to mix, and it seems to me, more oil=less wear. Have not had an engine failure in years. I just sold a 2001 Gas Gas 300. I changed the piston for the guy just to be safe, but it was fine. You are right. Changing engine components out that show now signs of wear is a waste of time.

This may have some merit...Maybe not lucky but maybe these engines have a lot larger tolerance range here than we are lead to believe.. I was reading an article once and it was pointing out how inefficient mixing the oil and gas really is at certain throttle ranges as too much of the mixture is blown out the exhaust. The answer is a oil pump that does the mixing...these were on bikes many years ago...and this pump will help cut down on emissions so don't be surprised if this old idea comes back in the future as the latest \ greatest thing.

I keep reading where 2-strokers will have FI shortly. Why have such a precise gas amount without a precise oil amount?

I always mix my oil the same. 5 gals of gas \ 1 pint of oil. Very easy mixing here. One brand of oil causes mass spooze out the pipe, another brand of oil, nana drop. And I should say I ride my bike the same also. Go figure