So, this rod is in a motorcycle, but I posted it here as it is more of a general engine oil question, not specifically motorcycle related. 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 got the old con rod back from the machinist, and it was hammered, from TDC to about 90 degrees around.
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?
Had rod bearing fail, any chance visc. choice?
- Thread starter greaso
- Start date
- Status
Couple different question on the bike. Is it a MX, Street, or dual sport, How many hours where on it when the big end went, what oci, and what fuel was used.
I dont think going thicker is going to be the answer, my mx quad with a yama 450 cc engine is pushing over 15:1, and lives its life at 10k rpms in racing, and i just replaced the crank this fall at 300 hours still tight, and thats always had 15w40 in it.
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.
I have 80-100 hours on the bike. It is an MX bike, basically. I change the oil every few rides, basically every 150 miles. 1.1 qt sump, shared oil with wet clutch. Yeah Chris, I probably did just get a bad one. That or detonation caused it. I run 92 octane, we have 10 percent ethanol here in Oregon. I was advised to run a gallon of 110 octane race gas to a 5 gallon jug of fuel, just to bump up the octane a bit. I will be doing this.
Edit: Chris, that is a very good point about 2-strokes living on 40:1. I never thought about that.
Last edited:
Take a look at the KTM forums. Normally there is a lot of collective knowledge on your specific bike, and allow you to compare notes with others.
I would consider trying Torco Accelerator. I am having issues with a heater pipe hitting the vacuum andvance on my GTO which is a car that already needs a little octane help. So anyway my timing was 15 degrees too high, had a half quart mixed with 10 gallons 93 and no pinging at all.
It looks like unfortunately you made a mistake in selecting the proper viscosity.
First, it's important to know that bearings are hydrodynamically lubricated, which means that they are only protected by the HTHS viscosity -- the more the HTHS viscosity, the more the minimal thickness of the oil film in the bearings.
10W-40 has an HTHS viscosity minimum spec (by SAE) of 3.5 cP. But then conventional 10W-40 shears (loses viscosity) a lot (if you are using a conventional 10W-40). Next time don't use anything less than a good (such as Delvac or Rotella) 15W-40 (conventional or synthetic), which has a min spec of 3.7 (by SAE) and the actual HTHS viscosity will be greater than 4.3 cP or so. 15W-40 also doesn't shear as much, and the used-oil HTHS viscosity will remain strong, too. Your best bet is probably a fully synthetic 20W-50 (or thicker oil) specifically made for motorcycles, which has plenty of ZDDP and moly in addition to a strong HTHS viscosity (greater than 4.3 cP or so).
Also, make sure to change your oil and oil filter frequently (as specified in the owner's manual) to ensure that contaminant particles don't score the bearings. Thicker oil film thanks to higher HTHS viscosity will encapsulate the contaminants better in the bearings.
Even if a 40 is on the thin side, failure at 80-100 hours shows a bad part, bad design, or faulty installation.
Go with Redline 20W-60 motorcycle oil (HTHS viscosity 7.0 cP) this time. Don't worry too much about the 10W- vs. 20W-, unless you're starting it well below freezing. It looks like your bearing design is not the best and therefore the highest HTHS viscosity out there will be your best protection against future bearing problems.
Light pinging usually doesn't hurt much and hard pinging or knocking should be easy to hear. If that's the case, troubleshoot your ignition and fuel systems or get a simple tune-up. Even if knocking is the issue, a higher HTHS viscosity will still help protect your bearings. Remember again that the bearings are hydrodynamically lubricated and the minimum oil-film thickness in the bearings is proportional to the HTHS viscosity. If your bearings are problematic due to bad design or high power density (power generated for a given engine size), simply get an oil with a strong HTHS viscosity, perhaps the one with the highest practical HTHS viscosity. The only minor drawback will be a small drop in fuel economy and horsepower, due to increased viscous friction in hydrodynamically lubricated areas (such as bearings).
I have a question on the rotella 15w40 recommendation for a bike with a wet clutch. Non of the diesel formulations offer 'wet clutch protection' as the motorcycle specific oil does. I questioned a buyer of the 5w40 synthetic which he said was going in a honda bike, apparently some forum uses were big on the 5w40 synthetic but at least 1 member mentioned some shifting issues. I have no idea what additives may be used for wet clutch.
Second point is the wisdom of using diesel formulations in gas engines. I was under the impression that the high detergent levels in diesel oil could have adverse effects on gas engines. Especially engines with fairly high rpm operations. When ci gave way to cj the levels of ZDDP in diesel were reduced which was one of the benefits of the diesel formula.
Diesel engines tend to operate at steady lower rpm's but gas engines rev to higher levels. I seem to recall some issue where the high detergent levels can compete with anti-wear additives on bearing and other wear surfaces. Course I could be all 'wet'
I know the rotella T-6 5w-40 has the JASO label for bikes with shared sumps. I use rotella's conventional 15w-40 in my Harleys primary and no ill effects
Consult motorcycle threads for recommendation of specific oils, wet clutches, etc. Your safest bet is using a motorcycle-specific oil with the proper certification -- MA, MB, etc. -- depending on the type of your clutch. Motorcycle engines are more demanding than gasoline and diesel engines, and they usually require synthetic oil with very high amounts of ZDDP, as well as a high HTHS viscosity, and the friction should be just right for a given type of clutch.
The main thing about diesel oils is that they are thicker, specifically higher HTHS viscosity. This is due to two things: diesels generate (1) higher torque at low RPMs and (2) abrasive soot particles. Both (1) and (2) necessitate more HTHS viscosity for a thicker oil film.
Your best bet for a gasoline engine is usually a gasoline-engine oil; although, a diesel-engine oil will also always work. Diesel oils have more detergents and dispersants as you said and they tend to fight for metal surfaces against antiwear additives. Their ZDDP is usually more the secondary type as opposed to primary, and secondary ZDDP is more an antioxidant than antiwear additive. Diesel oils are also meant for extended drain, at least 15,000 miles, which means they contain magnesium (Mg) for TBN retention. Mg can also increase corrosion and wear. Again, chances are that you can use a diesel oil in a gas engine safely and with very good or excellent results, but then while there are a lot of gasoline-specific oils out there, it's unnecessary. Needless to say, higher HTHS viscosity also decreases fuel economy and horsepower. Also, a oil that is too thick might sometimes not be as effective for lubrication of piston rings, as it may have a hard time flowing there, and it can unnecessarily increase bearing temperatures due to more viscous friction, when a thick oil film is not needed, which would then increase wear. It can also strain your oil pump, gaskets, and seals due to higher oil pressure generated by unnecessarily thick oil.
Lots of good advise here, thanks, I'll look to raise the HTHS, and will probably still use redline, just a thicker grade. Though I do have a jug and a half of Rotella t6 in that garage for the Subaru... Interesting comments about using diesel oil in high rpm motors.
Originally Posted By: Gokhan
Their ZDDP is usually more the secondary type as opposed to primary, and secondary ZDDP is more an antioxidant than antiwear additive.
Originally Posted By: greaso
Lots of good advise here, thanks, I'll look to raise the HTHS, and will probably still use redline, just a thicker grade. Though I do have a jug and a half of Rotella t6 in that garage for the Subaru... Interesting comments about using diesel oil in high rpm motors.
Originally Posted By: partspro
Diesel engines tend to operate at steady lower rpm's but gas engines rev to higher levels. I seem to recall some issue where the high detergent levels can compete with anti-wear additives on bearing and other wear surfaces. Course I could be all 'wet'
I'm going to go ahead and claim the failure is not oil related. In the aviation world, ball and roller bearings, with exceptionally high loads, are lubricated by very thin synthetics. (think jet engines and helicopter transmissions)
I'm also going to make the claim that the highest load your con rod bearings see in normal use, are inertial in nature. As the piston/rod assy is accelerated and decelerated at TDC and BDC with forces many times that of normal combustion (at high RPM of course) .
If possible, use a fuel with plenty of octane. It's a old "truth" that you need only so much octane for best performance. However, what many forget is that fuels with sufficient anti knock properties can result in better overall engine life under severe conditions. Even for engines with modest requirements. The piston aircraft world is an excellent example, as 8.5 to 1 compression engines don't have much need for octane. BUT, when conditions become severe, the additional octane of 100LL prevents engine failure.
There is also another factor in higher than needed octane. The slower burn often results in marginally lower peak pressures, offset by a slightly longer burn.
Interestingly enough, many turbocharged engines do not place higher loads on bearings and connecting rods when compared to the normally aspirated variant. As the tightly packed f/a mix in the turbocharged engine takes a few additional crankshaft degrees to complete it's burn.
Originally Posted By: Brent_G
I dont think going thicker is going to be the answer, my mx quad with a yama 450 cc engine is pushing over 15:1, and lives its life at 10k rpms in racing, and i just replaced the crank this fall at 300 hours still tight, and thats always had 15w40 in it.
Last edited:
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.
- Status
