oh no! the dreaded oil thread

[CaptonZap]

The other factor is I did a full valve check/adjustment and changed/swapped 12/16 shims on the 16v head. This was about 900 miles into the oil change with 5w-40 Rotella Syn.

.

Geez Bonz, you are as bad as Bill Clinton when it comes to all the facts.
Or as the old time radio guy said, "And now, the rest of the story"

The shims, in spite of looking smooth, are, on a microscopic level, still covered with peaks and valleys. Even if you took a shim out, looked at it, and put it back in, unless you put it in EXACTLY in the same orientation, the bedded in wear pattern would not be the same, and the two metal surfaces would start wearing away the high points to bed themselves in again.
So this next test will be a better indicator of wear, unless you do some other mechanic-ing on it.

CZ

[sthomag]

Yes, but is it at tight as a car or truck?

I don't know about the viscosity test, but I have seen multiple tests with thinner oil in other bikes and almost without fail more piston scuffing was seen. Simple to find out, go back to a 15w50 or 20w50 and see if the numbers drop back to where they were (hoping the walls/pistons aren't already damaged...)

A good 5w-40 oil (especially a good synthetic) should be about the same viscosity (or "thickness") as a 15w-40 when the engine is fully warm. The difference is when the engine is cold: it will flow better than the 15w-40 and lubricate better. When cold it will still be a lot thicker than either oil at operating temperature. Thus, I use Rotella T6 in my XS. If Shell made a 0w-40 Rotella syn with the right additives, I'd use that, because it would reduce wear on start-up and warm-up. In my cars, I go out of my way to use synthetics with 0w ratings, for that reason (Redline and Mobil 1).

You should get less wear with an oil that flows better AND provides a good oil film. Good synthetics tend to provide a stronger film, and flow much better at low temperature. Thick oil doesn't help if it's too viscous to flow and lubricate properly, given clearances, etc.

If Yamaha recommends oil rated at 40 hot viscosity, that's probably the best to use, unless someone has done a study that finds that higher or lower viscosities result in less wear. The Yamaha engineers knew what they were talking about. On the other hand, the lower the "w" rating the better: back 35 years ago, 5w-40 oils weren't really in the picture, and 10w-40s tended to wear out rather quickly.

[jetmechmarty]

A good 5w-40 oil (especially a good synthetic) should be about the same viscosity (or "thickness") as a 15w-40 when the engine is fully warm. The difference is when the engine is cold: it will flow better than the 15w-40 and lubricate better. When cold it will still be a lot thicker than either oil at operating temperature. Thus, I use Rotella T6 in my XS. If Shell made a 0w-40 Rotella syn with the right additives, I'd use that, because it would reduce wear on start-up and warm-up. In my cars, I go out of my way to use synthetics with 0w ratings, for that reason (Redline and Mobil 1).

You should get less wear with an oil that flows better AND provides a good oil film. Good synthetics tend to provide a stronger film, and flow much better at low temperature. Thick oil doesn't help if it's too viscous to flow and lubricate properly, given clearances, etc.

If Yamaha recommends oil rated at 40 hot viscosity, that's probably the best to use, unless someone has done a study that finds that higher or lower viscosities result in less wear. The Yamaha engineers knew what they were talking about. On the other hand, the lower the "w" rating the better: back 35 years ago, 5w-40 oils weren't really in the picture, and 10w-40s tended to wear out rather quickly.

Trouble is, the air cooled motorcycle engine/transmission beats the oil to death in a hurry. If the base oil is 0, that's where the oil is going as those polymer chains are broken down. True, synthetic oil is more durable than conventional oil, but it isn't bullet proof.

[sthomag]

Trouble is, the air cooled motorcycle engine/transmission beats the oil to death in a hurry. If the base oil is 0, that's where the oil is going as those polymer chains are broken down.

That's true to a degree, about conventional oils, although the additive packages are a lot more durable than they used to be. (I remember, decades ago, changing the oil in my VW Beetle after 2,000 miles, and it would run out like water. That kind of thing doesn't happen anymore: oil remains oily far longer.)

With synthetics, the story is a little different. Good synthetics, especially esters, are basically multigrade. That is, they behave as multigrade oils without modification. They simply don't thin out at high temperatures as much as petro-based oils do, and they have a much stronger, much more homogeneous molecular structure into the bargain.

A good synthetic multigrade should hold up better, even in an old bike engine, than even a single grade petroleum oil. It's a new era, and the old assumptions no longer apply.

You can test this using oil analysis. I started using 0w synthetics after analysis showed that they held up much better than 10w and 15w conventional oils in my car engines -- including my Honda S2000, which has a 2-litre 4 that revs to 9000 rpm and puts out 240 hp. They hold their viscosity and film strength well in bike engines, too. And the advantage of better flow at low temperatures is not to be sniffed at. Compromised lubrication at start-up and warm-up is responsible for most of the wear in your engine. It's a win-win.

[crazy steve]

A good 5w-40 oil (especially a good synthetic) should be about the same viscosity (or "thickness") as a 15w-40 when the engine is fully warm. The difference is when the engine is cold: it will flow better than the 15w-40 and lubricate better. When cold it will still be a lot thicker than either oil at operating temperature..

Sorry, that's not true. Multi-grade oils do not 'thicken' when hot. You'll still see that misinformation posted lots of places by people who should know better. The XS was designed for a 20w oil (whether it's a 20w40 or 20w50), that's what is best used in one.

You can easily check this; take some 5w40 and 20w50 and pour them through a viscometer while cold, noting the amount of time it takes. Then heat them to 200 degrees and do it again....

Where this causes a problem is at the cylinder walls/pistons. Theses are splash lubricated, and a too-thin oil runs off faster and doesn't leave a thick enough oil film. Use it at your peril....

[Bonz]

Do I understand you to be saying that the thinner oils run off the cylinder walls during engine use to the extent they compromise lubrication of the cylinder wall/piston?

I would think with even an 1100 rpm idle, the pistons are going up and down so fast, per se, that the oil wouldn't have any chance to run off the walls, honestly. The rings would be the factor in the oil moving off the walls as the pistons would be moving faster than gravity can work. Again, the pistons/rings move so fast, in a warm engine would it be of consequence?

Then we are back to cold start up being the major cause of wear, and a thinner oil shines at preventing wear in that respect, all other things equal.

I'm just thinking out loud here. I don't plan on running anything but 15w-40 in my XS's year round out here in Colorado, but the point is a good one to talk about regardless.

[motoman]

Do I understand you to be saying that the thinner oils run off the cylinder walls during engine use to the extent they compromise lubrication of the cylinder wall/piston?

I would think with even an 1100 rpm idle, the pistons are going up and down so fast, per se, that the oil wouldn't have any chance to run off the walls, honestly. The rings would be the factor in the oil moving off the walls as the pistons would be moving faster than gravity can work. Again, the pistons/rings move so fast, in a warm engine would it be of consequence?

Then we are back to cold start up being the major cause of wear, and a thinner oil shines at preventing wear in that respect, all other things equal.

I'm just thinking out loud here. I don't plan on running anything but 15w-40 in my XS's year round out here in Colorado, but the point is a good one to talk about regardless.

For longgivity, 20-50w the better option with air cooled engines havin' wider spread of temperature ranges, and corresponding less tight clearances, no matter which of the 50states it's in.

[crazy steve]

Do I understand you to be saying that the thinner oils run off the cylinder walls during engine use to the extent they compromise lubrication of the cylinder wall/piston?

I don't know if it 'runs off' too fast, but I've seen proof that thinner oils don't protect the cylinder walls as well under some circumstances. This has a been a long-standing issue with Harleys; guys get sold some 'trick of the month' oil that has a thinner viscosity and scuff the pistons/walls, sometimes to the point of failure. The LSR racers have found that under extreme conditions, not even the 20w50 cuts it; most run 50 or 60 straight-weight oil.

I ran 15w50 Mobil1 in my Sportster one time. The motor was markedly noisier, which I can't think is a good thing (remember, Harleys have separate oil just for the motor; the trans has it's own). Yes, I know these are 'better' oils, but they're designed for newer motors with tighter tolerances and better metallurgy in the parts. Multigrade oils weren't something 'new' when these bikes were built (having been around for well over 10 years) and Yamaha specified 20w40, not the much easier to find 10w30 or 10w40. They had a reason for that, and I'm not going to disagree....

[skids]

For longgivity, 20-50w the better option with air cooled engines havin' wider spread of temperature ranges, and corresponding less tight clearances, no matter which of the 50states it's in.

Maybe so, but in cold weather, you could get some starter clutch issues. I know the 20W number is supposed to control cold viscosity, but in my experiences, it doesn't. But hey, it is summer again!

[skids]

The first number is cold viscosity, and the second number is the hot viscocity that is controlled with polymers. With wet clutches, there is a lot of shearing that goes on and the polymers degrade. When a substantial amount of running time elapses, the second number gets closer to the first number... At least that is what I heard. So, if you want a more consistent oil, get a rating where the two numbers are closer together. OR don't get multi-viscosity OR change your oil on time!!!

[KA1J]

It's the change from 15W to 5W. Air-cooled motors have sloppier piston-to-cylinder clearances, and need a thicker oil that 'sticks' to the walls better. The walls are splash-oiled, so you don't want a too-fast runoff. That's why I don't even like using 15W, these bikes were designed for 20W. I've seen this same thing in tests on Harleys.

To visualize this, throw tomato juice on a wall, then use tomato sauce. Which will leave the thicker film?....

That... is a really good analogy.

[Bonz]

From everything I know, it is oil flow that keeps parts protected much more than any cling effect. Cling effect would come into play at start up, however that thicker oil (any oil) is hot when the bike shuts down and it runs back to the sump readily. Then you are fighting the thicker oil to get it circulating when you start up the next day.

From a protection standpoint I will take the flow over thickness anyday of the week. Oil flow is what helps cool parts and take heat away. Thicker oil, higher pressure, lower flow all else equal. Keep in mind pressure is a result of resistance to flow. Who wants oil being resistant to flow when they have a choice?

[trbig]

I've had two oiling issues that resulted in ruined engines while using 15w 40 oil. Coincidence? I guess it's possible, but well over 100k HARD miles on 20w 50 and still running strong. Good enough evidence for me.

[Bonz]

Out of interest and science, what were the oiling issues you had with 15w-40? Major engine failure, cam wear, etc?

Bummer it happened.

[trbig]

Out of interest and science, what were the oiling issues you had with 15w-40? Major engine failure, cam wear, etc?

Bummer it happened.

Crank bearing spun in one really nice running '78 motor, (Ruined crank and case was junk) and one crank bearing wipe out after 2500 miles after a rebuild, again, both using Rotella T 15w 40. Brand new crank bearings looked like you'd smeared copper pennies on them and it was knocking down deep. (Another junk crank)

I do have one oiling issue with the 20wt., though I really don't think that the clutch bearing at the case housing was designed for hundreds of wheelies. Even through this, the pistons/crank/cams are still standing up to some moron with a dirt bike mentality of, "If in doubt, burn out'."