Yamaha YZ85's seized (2)

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Originally Posted By: another Todd
Well actually he now says one seized the other he thinks burned a hole in the piston as it turns over but no compression. Fresh gas, Amsoil racing two stroke oil at 50:1.


What kind of gas was he using? I definatly would not run 50:1 in a 80cc bike at the sand dunes! Even using Asmsoil!

The smaller bore engines need more oil. IMO I would run Torco GP-7 @ 32:1.
 
50:1 is ridiculous. thats what outboards run. i dont care what amsoil or anyone else says. YAMAHA who made the danged things did not say to run 50:a. the manual probably said 25:1 if i had to guess.
 
Originally Posted By: Master ACiD
50:1 is ridiculous. thats what outboards run. i dont care what amsoil or anyone else says. YAMAHA who made the danged things did not say to run 50:a. the manual probably said 25:1 if i had to guess.


It's not ridiculous. Just because you think so? We have no idea what happened here. Maybe he hardly mixed the fuel, maybe he had huge sand ingress, maybe he did some misto chango to his jetting……sheesh…… Racers use Dominator at all sorts of mix ratios, including 50:1 and don’t hole pistons.
 
it's not because i think so. its because yamaha happen to think so.

i actually called the local yamaha dealer and asked them what mix ratio for a yz85. they said the manual states 20:1 for breakin and 25:1 for everyday running.
 
I'm not saying to ignore Yamaha's recommendations, but an oil needs to be mixed on the recommendations of the oil manufacturer as well. It's a balance.....the weather conditions, the engine tuning and jetting, the bike usage, the oil manufacturer, the engine manufacturer recommendations are all important. Using Amsoil Dominator 50:1 is fine for race conditions, but I know nothing more about this situation than is written above.

“Seized in 20 minutes”? To say the oil mixed at 25:1 would have prevented this is speculation, is what I should have written.
 
the oil manufacturer does not know if the oil is going in a yz85, a lawn boy mower, a pwc or a craftsman gas blower.

when you read a 2 stroke owners manual, they normally do not say "follow the instructions of the oil manufacturer" at least none of mine say that. they give you specific oil ratios to use and warn that deviating from these might result in damage.
 
Originally Posted By: Master ACiD
the oil manufacturer does not know if the oil is going in a yz85, a lawn boy mower, a pwc or a craftsman gas blower.
Correct - that's exactly why some oil manufacturers make different kind of oils for different engines.

Originally Posted By: Master ACiD
when you read a 2 stroke owners manual, they normally do not say "follow the instructions of the oil manufacturer" at least none of mine say that. they give you specific oil ratios to use and warn that deviating from these might result in damage.
That's part of the problem, no matter what the oil, mix it at this ratio - but oil brands vary a lot. Some can be run more dilute than others, because they have a heavier base oil, different additives. Not all oils should be diluted the same.

Should this little screaming engine be run at 50:1? Maybe not. I would say 35:1 or so. Did it cause it to seize in 20 minutes? No.
 
The ratio, per se, did not cause the failure. Nor would any ratio cause a failure. It is the metering of the fuel/oil/air that affects the combustion.

If you are running a 50:1 ratio and the bike is close to being lean, simply going to more oil, like a 20:1 ratio, will probably result in a leaned out holed piston.
But, why? you may ask...well, even though you added more oil, you have effectively robbed some of the area used for fuel and air. You have leaned the bike out even further by adding more oil.

One should listen more to a mechanic over an oil salesman on this issue. And this may bring about some controversy, but when decisions can result in a very expensive failure, it's best to know what is really happening, rather than trust the logic and sales pitches of salesmen and the less-than-learned guessers.

A small bore 2T engine needs to have more protection than a larger bore. There is simply more happening in a small, high revving engine than with the bigger jugs.

A rule of thumb that many professionals follow, is to use a ratio of approx. 18-32:1 on bores with 125cc's or less. 32:1 on the larger bores.

No matter what ratio you pick, you need to jet the bike so it meters that mixture properly.
Arguing about mix ratio is really not the issue anyway, it is how the mixture is metered that makes or breaks an engine.
 
I actually agree with Jaybird....for the most part.

There are some "oil salesmen" that know more than some so called "mechanics". Mechanics can play favorite oil games, too. But generically I will say, just to mix what a salesweenie says, or the bottle says or a web site says or even a mechanic says may NOT be correct.

A knowledgeable mechanic that jets the bike is invaluable as a starting point, no doubt about that. Playing with the jetting yourself without knowledge is worse than playing 32:1 vs. 50:1.

But agreed 32:1 vs. 35:1 is spliting hairs and not what this post is about. I doubt we'll see pictures or get the real answer at this point.
 
I disagree that richening the oil mixture will have much of an effect on lean-ness unless it thickens the fuel up so much that it creates higher resistance (less flow) through the jets.

You are replacing a combustible hydrocarbon with another combustible hydrocarbon, air fuel ratio should stay the same (excepting the above).

May also lower your octane into the bad zone 'though.
 
50:1 is not to lean. Belray recommends that and Ive seen engines tore down at that ratio and they looked excellent. Ive always used Yamalube 2R and ran it at 40:1 without any problems in 125s. The manufactur is going to put the richest mixture on that back fender, because you could be using a junk noname lawn care oil, possibly even a straight 30 wt, in it and they need it to be on the rich sides, the new bikes also come about a jet too high on the rich side. 50:1 is not too high with a name brand synthetic such as Belray or Amsoil. Yamalube 2R is a syn/blend. If you are shooting for performance then you will re jet and adjust the oil gas ratio to the perfect combo. More oil will lead to a leaner condition, more oil, less gas to the same amount air, so more oil as you state will only worsen a lean condition.
 
http://www.locastros.com/piston_oil_ratios.htm


This link compares 1 persons results based on personal parts inspection 32 vs 50:1 with the oil in question. This was on 250cc bike that generally would have slower migration time of the oil than a 85cc, so thus would demand less oil all things being equal.

I doubt that the 50:1 mix in the 85's caused the failures, detonation from too lean of fuel mixture for the long hard sand pulls, and or overheating would be my guess. Too lean oil ratio shows up as accelerated wear , basically a slow death not a quick failure.


There is no perfect ratio IMO, it's engine and application, use, specific. The same kawi 250 in that link would be fine at 50:1 as a tight woods racer. The 85's probably fine also as playbikes, put a paddle on them and go to the dunes, or mx them, and all bets are off.
 
Shannow, if the bike has been jetted up correctly for use with a 50:1 fuel/oil ratio, going to a 20:1 ratio could leave the bike dangerously close to piston meltdown, as lean conditions run extremely hot. I have seen this on many occasions first hand.
Try holding a lit match to a cup full of Yamalube. Now try the gasoline....
Besides, very little oil reaches the combustion chamber, IF the engine is metering the fuel mix properly.

Some bikes do carry a very rich mixture recommendation, and I suspect it to be a CYA thing, as Panzerman describes it. However, the "jet is upped on size" thing is not really the case.
The mfg knows that the correct ratio is dependent on engine and use specifics, and that proper metering of the air/fuel/oil mixture is dependent on many variables such as quality of fuel, air temperature, relative humidity, and elevation.
The mfg simply cannot provide a catch-all metering scenario, as his equipment is sold to areas with a wide array of conditions.
The jetting chosen for a factory bike is basically an arbitrary median average. It may be rich for one man, but the next man may find it lean.

Many will want to add less oil to their 2cycle engine when they see a dark, oily spooge coming from the tailpipe. It would seem logical that if there is oil coming from the tailpipe, that the mixture is carrying too much oil...
But that is again where conventional wisdom separates from facts.
When an engine is producing this oily residue, it is probably due to the mixture not being metered properly by the carb, and as a result much of the FUEL and it's components gets past complete combustion, and turns itself into an oily looking substance along with a small amount of the oil that didn't fall out of suspension prior to combustion.
Adding less oil will not fix the spooging problem, but rather enhance it, since you have now added more fuel to the mix...and the metering devices (jets, needle, etc) are already allowing too much fuel into the chamber to begin with. The result is even more oily fuel spooge, and the engine a bit less powerful.

A properly set up engine, that is metering the fuel/oil/air mixture to optimum, will see most every bit of the oil fall out of suspension prior to the combustion chamber. If the remaining fuel/air mixture results in about a 12-16:1 air/fuel ratio, then the resulting burn will be clean and powerful.
The goal of the tuner is to find this scenario and keep it there. It's a moving target, so the pro tuner has to be very sharp about these things, and know exactly what effects the changes make.
As there is no catch-all weather, there is no catch-all jetting.
But the optimum jetting can be found at any given time, and the fuel/oil ratio is yet another tool that can be used to find the optimum burn.
 
Jaybird,
respectfully, it's the point midway between 12 and 16 to 1 that is the hottest.

Lean of stoichiometric is cool, rich of stoichiometric is cold. Stoichiometric is HOT.

For the lube not to make it into the combustion process, where does it go ?

Flash point has next to nothing to do with flammability of either the fuel or the oil.

I WILL admit that higher oil ratios will push the mix closer to detonation (extremely high temperatures), and may lean down the overall air to hydrocarbon ratio by a bit.

If your assertion that too rich running leads to wet exhausts, through some sort of polymerisation process were correct, my 323i would leave a snail trail of oily looking stuff at present time.
 
Sure some oil goes through combustion. But the metering of the fuel mixture must be so that some of the oil falls out of suspension. This re condensed oil then migrates to lube the friction surfaces of the crank bearings, as well as some of it being pulled into combustion.

Much of the oily residue from an incomplete burn are from components of the fuel. Even a well jetted engine running at optimum will probably not burn all the components of LL avgas, or fuel from the local swill.

And I agree that flash point has very little to do with this equation, but volatility and difference in distillation curve between fuel and oil does.

Your 323i should maybe have the EFI and the oxygen sensor looked at.
The engines we are talking about have no such animals.
And no matter what ratio we are talking, my assertion is that it's the brass in the carb that makes the greatest changes at any given circuit.
I also assert that changing the ratio can tweak these carb settings across the total range pf circuits, which can be a very handy tool to the competent tuner.

It is not hard to visualize a kid racing full out on a bike that is jetted up near perfect for the conditions, and at the very edge of too lean (which is where this most complete and powerful burn is found), and then switching his fuel to one that has much more oil in it. If you think that running leaner than stoich, is a cool burn...try explaining that to the kid with the holed out piston.

Just as little tweaks in the temps or rel humidity can completely change how a high performancne 2stroke runs, so can the slight tweaks of fuel ratios and carb settings.
 
The best, quickest way to see if it was running lean is check the plug. This is the gauge which you use to jet, Which I may add is a nightmare to get right, If it is white and looks new after a ride, you are too lean, black is too rich and light to choc. brown is about perfect. The spark plug will give you a fairly accurate point of where you are at. I agree that a high oil/gas ratio and/or a low quality oil will give the bike a slow death with piston scuffing and rings going by-by, seldom does it seize them up permanently. I have heard of cranks being wiped out and the owners have blamed the oil, but I have never had it happen to me and Ive had over 20 bikes over the years, I suspect over revving or overrunning had more to do with it but they didnt admit it.
 
Originally Posted By: Jaybird
Your 323i should maybe have the EFI and the oxygen sensor looked at.


If I had O2 sensors, I'd be checking them.

This is a leaded fuel era engine, and has no O2 sensors. Essentially all open loop...need to check the injectors, as I'd not be surprised if they haven't been "upgraded" along with all the other "upgrades" that the wierd previous owner did.

Originally Posted By: Jaybird
I also assert that changing the ratio can tweak these carb settings across the total range pf circuits, which can be a very handy tool to the competent tuner.

It is not hard to visualize a kid racing full out on a bike that is jetted up near perfect for the conditions, and at the very edge of too lean (which is where this most complete and powerful burn is found), and then switching his fuel to one that has much more oil in it. If you think that running leaner than stoich, is a cool burn...try explaining that to the kid with the holed out piston.


I agree with you.
 
There's a big difference between a weedwhacker and a motorbike.

Constant speed 2-strokes have a constant lubrication requirement.

Variables, like bikes may be putting along at low speeds (low oil throughput), then suddenly be required for a full throttle high rev situation.

The interim period can be bad from a lubrication perspective.
 
I go with the sand, it will pentrate foam airfilters if quality tacky filter oil is not used. just check the air boot past the filter for any residual, there should be no dust in there at all.

Actually under pure dry sand conditions, running panty hose over your arrbox openings can help alot too with filtering
 
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