Had rod bearing fail, any chance visc. choice?

[Cujet]

Originally Posted By: Keith Z
Another thing to consider is carb jetting. I have had a [censored] of a time correctly jetting my ktm 200 and 300 bikes.
Granted they are not 4 strokes but KTMs are very particular about jetting. You should try one of the JD jet kits, they work very well and are worth the money. They will help eliminate any detonation you may be having and I would mix in some race fuel at every fill up. Good luck.


I think the 350 4t is fuel injected. Not to say that fuel/air mix can't be a problem with injected engines either. Not sure how that system compensates for ethanol content.

In this case, I'd much prefer to stick with conventional leaded race gas or 100LL avgas. That way, the variable ethanol content is never a factor.

I'd put money on longer crank life too.

 

[AEHaas]

I agree with the comment that 2 strokers have used virtually gasoline to lubricate high output engines for years in these bearing areas.

If you are living in a cooler environment and revving up early, before the OIL temperatures are up, too viscous an oil may be a large contributor. I bet you had cavitation issues, these are much more likely to cause problems with far less milage on the engine.

You should at least consider the use of a Thinner oil.

These may help you understand viscosity issues, the first one is more current:

http://ferrarichat.com/forum/faq.php?faq=new_faq_item#faq_haas_articles

Original (but edited by others) version:

http://www.bobistheoilguy.com/motor-oil-101/

aehaas

 

[Gokhan]

Here is a great reference:

Effect of low-viscosity oils on engine bearings

It details the effect of viscosity on bearing failure. Here is an excerpt:

"One of the consequences though of lowering oil viscosity is a decrease of the minimum oil-film thickness. ... This increases the failure threat level of such factors as surface roughness, shaft grinding irregularities, oil-borne foreign particles and geometrical distortions and misalignments. Direct metal-to-metal intermittent contact between the surfaces occurs more frequently. The wear rate is increased due to the direct metal-to-metal contact.

...

Another problem of low viscosity oils is associated with the distribution of oil pressure over the bearing surface. The pressure distribution in low viscosity oil is less uniform -– the peak pressure is higher therefore the load applied to the bearing material in this particular area is higher. This may cause fatigue if the fatigue strength of the material is insufficient. The effect of low viscosity oil on the pressure distribution may be compensated by a decrease of the bearing clearance."

Also see the other topics on that Web site, including:

Engine-bearing failure

 

[Cujet]

Of course, this is a roller bearing, and, as such, has very different lubricant requirements.

 

[Ken2]

Other things remaining equal, higher viscosity oil has higher film strength.

As Cujet posted, the bearing in question is an antifriction bearing, not a sleeve bearing. Hydrodynamic lubrication does not come into play.

My Suzuki V-Strom runs great on diesel engine oil at 10,000 rpm. And my Volvo turbo runs up to 5000 rpm on the same oil. Any idea how fast a big rig turbocharger is spinning? (over 100,000 rpm?) Who said that diesel lube wasn't for high speed engines? Many, many riders have 100,000 miles or more on their engines with HDEO. Shell did submit their Rotella oils for wet clutch testing and passed. Others work fine, but haven't been lab-tested and certified--my choice is Schaeffer #9000 5W-40.

There is lot's of misinformation and unknowns about friction modifiers and wet clutches. Schaeffer's #707 20W-50 motorcycle oil is both JASO-MA2 certified and contains two friction modifiers, moly and Schaeffer's proprietary Penetro.

 

[crazyoildude]

i dont know motorcycles but as for car and truck engines if they call for 5w20 use it because some bearing clearances are so tight that a thicker oil cant reach the middle

 

[Gokhan]

Originally Posted By: crazyoildude
i dont know motorcycles but as for car and truck engines if they call for 5w20 use it because some bearing clearances are so tight that a thicker oil cant reach the middle

That's definitely not the reason and it's certainly a myth. Read the references and other links at those great, detailed technical references I gave above. You can safely use a thicker oil with smaller bearing clearances; except, it will run hotter -- therefore, choice of viscosity is a compromise between larger minimum oil-film thickness and less chance of metal-to-metal contact (with thicker oil) and cooler bearings (with thinner oil). It's more like you shouldn't use thin oil with larger bearing clearances as opposed to thick oil with smaller bearing clearances, as thin oil with large bearing clearances can cause large pressure peaks (P_max in the picture below) in the bearings that could cause damage. Also, for example, bearing clearances and diameters in my 1985 Corolla that specify xW-30 - xW-50 are more or less the same as 2011 Corolla that only specify 0W-20.

It is probably usually wise to go with manufacture's specs. For example, if your BMW, Mercedes, or Rolls-Royce calls for ACEA A3/Bx (HTHS >= 3.5 cP), there may be a chance that a 0W-20 (HTHS = 2.6 cP) can cause damage to the bearings. Again, read the references above to understand how the bearings are designed and oil viscosity comes to play. At the end, the oil viscosity depends on the bearing geometry and design.

 

[Gokhan]

Originally Posted By: Ken2
Other things remaining equal, higher viscosity oil has higher film strength.

As Cujet posted, the bearing in question is an antifriction bearing, not a sleeve bearing. Hydrodynamic lubrication does not come into play.

My Suzuki V-Strom runs great on diesel engine oil at 10,000 rpm. And my Volvo turbo runs up to 5000 rpm on the same oil. Any idea how fast a big rig turbocharger is spinning? (over 100,000 rpm?) Who said that diesel lube wasn't for high speed engines? Many, many riders have 100,000 miles or more on their engines with HDEO. Shell did submit their Rotella oils for wet clutch testing and passed. Others work fine, but haven't been lab-tested and certified--my choice is Schaeffer #9000 5W-40.

There is lot's of misinformation and unknowns about friction modifiers and wet clutches. Schaeffer's #707 20W-50 motorcycle oil is both JASO-MA2 certified and contains two friction modifiers, moly and Schaeffer's proprietary Penetro.

There is no mystery about wet clutches and friction modifiers. Wet clutches require a certain range of friction coefficient -- too much friction or too little friction will cause the clutch not to function properly. JASO MA, MB, MA1, and MA2 specify the allowed range of the friction coefficients. See Page 3 in the latest JASO specification for the allowed friction coefficients. You should pick up an oil with the correct spec to ensure that your clutch will work. Regarding friction modifiers, friction coefficient is determined not only by friction modifiers but also the oil viscosity. A thick oil's friction coefficient can still fall into a JASO MA, MA1, or MA2 range (high coefficient) even with a considerable amount of friction modifiers.

Yes, there is nothing wrong with using HDEO in gas and motorcycle engines, as long as you and your engine are comfortable with the higher SAE kinematic viscosities (usually xW-40) and higher HTHS apparent viscosities (for CJ-4, greater than or equal to 3.5 cP). This said, application-specific oils are still the best bet: use PCMO for gas engines, HDEO for diesels, and dedicated motorcycle oil for motorcycle engines for the best performance.

Here is a nice article by the ExxonMobil/Shell additive company Infineum on using application-specific oil:

Dedicated motorcycle oils deliver ultimate protection

 

[greaso]

Gokhan, I do find myself lugging the engine. The bike is fuel injected and I often find myself in 3rd gear climbing a hill really slowly.. because the bike "carborates" so well.
I have the bike assembled and running now. I now feel that the failure was not oil related, but part or assembly related, from the factory. The bike has always been a bear to kick over for a little 350. Just felt tight. Either the con rod bearing was faulty or the miniscule .006 ring end gap of the (used) ring had something to do with it. The old piston pin was also tight, so I feel it was parts related, not oil related. With a new piston and properly gapped rings, and a new con rod, the bike kicks over like it should. I'm going to still increase my viscosity, stick with Redline oil and try to not lug the little thing too much.

 

[crazyoildude]

i have owned a very busy engine shop for over 20 years and i have seen with my own eyes that some engines especially with wide bearings like the 4.6 for instance have more bearing wear with thicker oil.. It is also a well known fact that using 5w20 in those engines have less valve wear and the ones that people use thicker oil in have valve guide issues..That was discussed in a number of engine tech classes.
If the engine manufacture tells you to use 5w20 its a good idea to use 5w20.... Im not saying 5w30 will cause an engine to blow im saying 5w20 is better...Back in the day before i knew better i always used 10w40..
Also thinner oil runs cooler and the bearings usually last longer..
even most racing teams use the thinner oils

 

[Gokhan]

Originally Posted By: greaso
Gokhan, I do find myself lugging the engine. The bike is fuel injected and I often find myself in 3rd gear climbing a hill really slowly.. because the bike "carborates" so well.
I have the bike assembled and running now. I now feel that the failure was not oil related, but part or assembly related, from the factory. The bike has always been a bear to kick over for a little 350. Just felt tight. Either the con rod bearing was faulty or the miniscule .006 ring end gap of the (used) ring had something to do with it. The old piston pin was also tight, so I feel it was parts related, not oil related. With a new piston and properly gapped rings, and a new con rod, the bike kicks over like it should. I'm going to still increase my viscosity, stick with Redline oil and try to not lug the little thing too much.

I agree. At first, I thought that you had sliding bearings. With roller bearings, it's a somewhat different story. It almost certainly looks like it wasn't oil-related for the most part.

Here is a very good detailed technical read on roller bearings if you have time. Higher operating viscosity, which results in larger minimum oil-film thickness, and generous amounts of ZDDP and moly, which protect against wear and score, help with roller bearings. Therefore, I would recommend a motorcycle-specific oil of manufacturer-recommended viscosity (xW-50 or xW-60) heavily loaded with ZDDP and moly. Also, as others recommended, don't rev up until oil warms up, especially in cold weather with 20W-x, so that you ensure proper oil flow with cold engine. Try not to lug the engine if possible, as lugging will decrease the minimum oil-film thickness due to smaller viscous reaction force with lower RPM, and hence you will transition from elastohydrodynamic-lubrication regime in the roller bearings to mixed lubrication (occasional metal-to-metal contact) and then to boundary lubrication (constant metal-to-metal contact).

 

[A_Harman]

greaso,

This is an excellent thread with a lot of good references.

I'm not clear from my reading of the thread if the rod bearing was actually failed, but since you said the rod was hammered from TDC to 90 after, I'm assuming the bearing was hurt, too. If so, the crank journal probably has surface distress. If you have put the engine back together with a new rod and bearing, but reused the crank, I worry about the life of the new bearing.

 

[Jeff_in_VABch]

Gokhan, you really blew it on this one. Have you ever even assembled a motorcycle engine?

At least you finally realized motorcycles use roller bearing rods.

 

[Gokhan]

No, I don't rebuild motorcycle engines. But you should also know that plain bearings are also very common in motorcycle engines.

In any case I provided two great technical references above for both plain and roller bearings. They have everything you want to know.

It turns out that effects of oil viscosity in both types of bearings are similar. Higher viscosity ensures oil film in either type of bearing but then runs hotter. My posts above along with the technical references describe the effect of oil viscosity in detail for either bearing type. I am sure they will be very useful for the original poster in choosing an oil.

 

[greaso]

I spent some time reading the technical article about bearings, wow, there is a ton of info. The paper mentioned contaminants in the oil as a big contributor to failed bearings, and the bike has a wet clutch and tranny sharing the same oil. Yes, there is a filter, but I can see that changing the oil and filter often isn't just about the oil breaking down, it is to keep contaminants from building up. Thanks for all the good info.

 

[Jeff_in_VABch]

Originally Posted By: Chris142
Those roller bearings don't need much lube. A 10wxx or 20wxx is more than enough. The 2 strokes live a long time on 40-1 and 50-1. I think you just got a bad one.


They definately dont need much oil.

It's a shame they aren't incorporated into more automotive engines. I guess the noise and cost are deal breakers compared to the reduced friction and lower oil temperature benefits.

 

[Wilhelm_D]

Originally Posted By: greaso
I just had a new con rod (roller bearing type) pressed in my crank, the old con rod bearing failed in a relatively short period of use. I suspect detonation was the cause, but want to make sure that my alternative oil weight choice was not at fault- before I choose a new oil for the repaired engine. The bike is a KTM 350 4-stroke, and it specs a 10-50 and 10-60 oil. It specifies Motorex oil, after searching here, Motorex oils seem to be on the light side of the viscosity range, so I figured Redline 10-40 (with a little 20-50 mixed in in the summer) should work well as Redline oil tends to be on the thicker side. The engine has a high stock compression of 13.5 to 1, which must be hard on the crank. I realize that the failure is probably not oil related, but I don't want to go through this again….. I said that I suspected detonation, but I have only heard knocking a handful of times, though I realize that I may not always be able to hear it over the engine noise. Could the lighter viscosity been at fault?


I would tend to doubt it.

The kind of failure you’re talking about sounds like something else, possibly improper assembly. Detonation would show up on the piston head and since you’ve disassembled the engine I take it did not.

Here are some viscosity numbers on Mobil 1 and Redline motorcycle oils, Mobil 1 Racing 4T 10W-40, V-Twin 20W-50, Redline 10W-40 and 20W-50.

cSt @ 40°C – 4T = 82, V-Twin = 172.3, RL 10W-40 = 88.7, RL 20W-50 138

cSt @ 100°C - 4T = 13.1, V-Twin = 28, RL 10W-40 = 14, RL 20W-50 18.6

There are others out there, but these are the two brands I am most familiar with.

 

[Kestas]

Without doing a full-blown failure analysis, it's almost impossible to find the root cause of your failure.

Going with percentages, the number one cause for bearing failure is poor installation. Number two is horrible failure of the lubrication (i.e., contamination, water, no lube, blocked lube). I have to agree with Chris - you'd be surprised how little effect the grade of oil has on lubricating roller bearings, or how little lube is needed to lubricate roller bearings.